add libcore from 2016-04-11 nightly

1 files changed, 1636 insertions, 0 deletions

diff --git a/libcore/fmt/mod.rs b/libcore/fmt/mod.rs
new file mode 100644
index 0000000..2f02f5c
--- /dev/null
+++ b/libcore/fmt/mod.rs
@@ -0,0 +1,1636 @@
+// Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Utilities for formatting and printing strings.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use prelude::v1::*;
+
+use cell::{UnsafeCell, Cell, RefCell, Ref, RefMut, BorrowState};
+use marker::PhantomData;
+use mem;
+use num::flt2dec;
+use ops::Deref;
+use result;
+use slice;
+use str;
+
+#[unstable(feature = "fmt_flags_align", issue = "27726")]
+/// Possible alignments returned by `Formatter::align`
+#[derive(Debug)]
+pub enum Alignment {
+    /// Indication that contents should be left-aligned.
+    Left,
+    /// Indication that contents should be right-aligned.
+    Right,
+    /// Indication that contents should be center-aligned.
+    Center,
+    /// No alignment was requested.
+    Unknown,
+}
+
+#[stable(feature = "debug_builders", since = "1.2.0")]
+pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap};
+
+mod num;
+mod builders;
+
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+           issue = "0")]
+#[doc(hidden)]
+pub mod rt {
+    pub mod v1;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+/// The type returned by formatter methods.
+pub type Result = result::Result<(), Error>;
+
+/// The error type which is returned from formatting a message into a stream.
+///
+/// This type does not support transmission of an error other than that an error
+/// occurred. Any extra information must be arranged to be transmitted through
+/// some other means.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Copy, Clone, Debug)]
+pub struct Error;
+
+/// A collection of methods that are required to format a message into a stream.
+///
+/// This trait is the type which this modules requires when formatting
+/// information. This is similar to the standard library's `io::Write` trait,
+/// but it is only intended for use in libcore.
+///
+/// This trait should generally not be implemented by consumers of the standard
+/// library. The `write!` macro accepts an instance of `io::Write`, and the
+/// `io::Write` trait is favored over implementing this trait.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Write {
+    /// Writes a slice of bytes into this writer, returning whether the write
+    /// succeeded.
+    ///
+    /// This method can only succeed if the entire byte slice was successfully
+    /// written, and this method will not return until all data has been
+    /// written or an error occurs.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an instance of `Error` on error.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write_str(&mut self, s: &str) -> Result;
+
+    /// Writes a `char` into this writer, returning whether the write succeeded.
+    ///
+    /// A single `char` may be encoded as more than one byte.
+    /// This method can only succeed if the entire byte sequence was successfully
+    /// written, and this method will not return until all data has been
+    /// written or an error occurs.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an instance of `Error` on error.
+    #[stable(feature = "fmt_write_char", since = "1.1.0")]
+    fn write_char(&mut self, c: char) -> Result {
+        self.write_str(unsafe {
+            str::from_utf8_unchecked(c.encode_utf8().as_slice())
+        })
+    }
+
+    /// Glue for usage of the `write!` macro with implementors of this trait.
+    ///
+    /// This method should generally not be invoked manually, but rather through
+    /// the `write!` macro itself.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write_fmt(&mut self, args: Arguments) -> Result {
+        // This Adapter is needed to allow `self` (of type `&mut
+        // Self`) to be cast to a Write (below) without
+        // requiring a `Sized` bound.
+        struct Adapter<'a,T: ?Sized +'a>(&'a mut T);
+
+        impl<'a, T: ?Sized> Write for Adapter<'a, T>
+            where T: Write
+        {
+            fn write_str(&mut self, s: &str) -> Result {
+                self.0.write_str(s)
+            }
+
+            fn write_char(&mut self, c: char) -> Result {
+                self.0.write_char(c)
+            }
+
+            fn write_fmt(&mut self, args: Arguments) -> Result {
+                self.0.write_fmt(args)
+            }
+        }
+
+        write(&mut Adapter(self), args)
+    }
+}
+
+#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
+impl<'a, W: Write + ?Sized> Write for &'a mut W {
+    fn write_str(&mut self, s: &str) -> Result {
+        (**self).write_str(s)
+    }
+
+    fn write_char(&mut self, c: char) -> Result {
+        (**self).write_char(c)
+    }
+
+    fn write_fmt(&mut self, args: Arguments) -> Result {
+        (**self).write_fmt(args)
+    }
+}
+
+/// A struct to represent both where to emit formatting strings to and how they
+/// should be formatted. A mutable version of this is passed to all formatting
+/// traits.
+#[allow(missing_debug_implementations)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Formatter<'a> {
+    flags: u32,
+    fill: char,
+    align: rt::v1::Alignment,
+    width: Option<usize>,
+    precision: Option<usize>,
+
+    buf: &'a mut (Write+'a),
+    curarg: slice::Iter<'a, ArgumentV1<'a>>,
+    args: &'a [ArgumentV1<'a>],
+}
+
+// NB. Argument is essentially an optimized partially applied formatting function,
+// equivalent to `exists T.(&T, fn(&T, &mut Formatter) -> Result`.
+
+enum Void {}
+
+/// This struct represents the generic "argument" which is taken by the Xprintf
+/// family of functions. It contains a function to format the given value. At
+/// compile time it is ensured that the function and the value have the correct
+/// types, and then this struct is used to canonicalize arguments to one type.
+#[derive(Copy)]
+#[allow(missing_debug_implementations)]
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+           issue = "0")]
+#[doc(hidden)]
+pub struct ArgumentV1<'a> {
+    value: &'a Void,
+    formatter: fn(&Void, &mut Formatter) -> Result,
+}
+
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+           issue = "0")]
+impl<'a> Clone for ArgumentV1<'a> {
+    fn clone(&self) -> ArgumentV1<'a> {
+        *self
+    }
+}
+
+impl<'a> ArgumentV1<'a> {
+    #[inline(never)]
+    fn show_usize(x: &usize, f: &mut Formatter) -> Result {
+        Display::fmt(x, f)
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+               issue = "0")]
+    pub fn new<'b, T>(x: &'b T,
+                      f: fn(&T, &mut Formatter) -> Result) -> ArgumentV1<'b> {
+        unsafe {
+            ArgumentV1 {
+                formatter: mem::transmute(f),
+                value: mem::transmute(x)
+            }
+        }
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+               issue = "0")]
+    pub fn from_usize(x: &usize) -> ArgumentV1 {
+        ArgumentV1::new(x, ArgumentV1::show_usize)
+    }
+
+    fn as_usize(&self) -> Option<usize> {
+        if self.formatter as usize == ArgumentV1::show_usize as usize {
+            Some(unsafe { *(self.value as *const _ as *const usize) })
+        } else {
+            None
+        }
+    }
+}
+
+// flags available in the v1 format of format_args
+#[derive(Copy, Clone)]
+#[allow(dead_code)] // SignMinus isn't currently used
+enum FlagV1 { SignPlus, SignMinus, Alternate, SignAwareZeroPad, }
+
+impl<'a> Arguments<'a> {
+    /// When using the format_args!() macro, this function is used to generate the
+    /// Arguments structure.
+    #[doc(hidden)] #[inline]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+               issue = "0")]
+    pub fn new_v1(pieces: &'a [&'a str],
+                  args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
+        Arguments {
+            pieces: pieces,
+            fmt: None,
+            args: args
+        }
+    }
+
+    /// This function is used to specify nonstandard formatting parameters.
+    /// The `pieces` array must be at least as long as `fmt` to construct
+    /// a valid Arguments structure. Also, any `Count` within `fmt` that is
+    /// `CountIsParam` or `CountIsNextParam` has to point to an argument
+    /// created with `argumentusize`. However, failing to do so doesn't cause
+    /// unsafety, but will ignore invalid .
+    #[doc(hidden)] #[inline]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
+               issue = "0")]
+    pub fn new_v1_formatted(pieces: &'a [&'a str],
+                            args: &'a [ArgumentV1<'a>],
+                            fmt: &'a [rt::v1::Argument]) -> Arguments<'a> {
+        Arguments {
+            pieces: pieces,
+            fmt: Some(fmt),
+            args: args
+        }
+    }
+}
+
+/// This structure represents a safely precompiled version of a format string
+/// and its arguments. This cannot be generated at runtime because it cannot
+/// safely be done so, so no constructors are given and the fields are private
+/// to prevent modification.
+///
+/// The `format_args!` macro will safely create an instance of this structure
+/// and pass it to a function or closure, passed as the first argument. The
+/// macro validates the format string at compile-time so usage of the `write`
+/// and `format` functions can be safely performed.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Copy, Clone)]
+pub struct Arguments<'a> {
+    // Format string pieces to print.
+    pieces: &'a [&'a str],
+
+    // Placeholder specs, or `None` if all specs are default (as in "{}{}").
+    fmt: Option<&'a [rt::v1::Argument]>,
+
+    // Dynamic arguments for interpolation, to be interleaved with string
+    // pieces. (Every argument is preceded by a string piece.)
+    args: &'a [ArgumentV1<'a>],
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a> Debug for Arguments<'a> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result {
+        Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a> Display for Arguments<'a> {
+    fn fmt(&self, fmt: &mut Formatter) -> Result {
+        write(fmt.buf, *self)
+    }
+}
+
+/// Format trait for the `?` character.
+///
+/// `Debug` should format the output in a programmer-facing, debugging context.
+///
+/// Generally speaking, you should just `derive` a `Debug` implementation.
+///
+/// When used with the alternate format specifier `#?`, the output is pretty-printed.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// This trait can be used with `#[derive]`.
+///
+/// # Examples
+///
+/// Deriving an implementation:
+///
+/// ```
+/// #[derive(Debug)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// println!("The origin is: {:?}", origin);
+/// ```
+///
+/// Manually implementing:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl fmt::Debug for Point {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         write!(f, "Point {{ x: {}, y: {} }}", self.x, self.y)
+///     }
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// println!("The origin is: {:?}", origin);
+/// ```
+///
+/// This outputs:
+///
+/// ```text
+/// The origin is: Point { x: 0, y: 0 }
+/// ```
+///
+/// There are a number of `debug_*` methods on `Formatter` to help you with manual
+/// implementations, such as [`debug_struct`][debug_struct].
+///
+/// `Debug` implementations using either `derive` or the debug builder API
+/// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
+///
+/// [debug_struct]: ../../std/fmt/struct.Formatter.html#method.debug_struct
+///
+/// Pretty printing with `#?`:
+///
+/// ```
+/// #[derive(Debug)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// println!("The origin is: {:#?}", origin);
+/// ```
+///
+/// This outputs:
+///
+/// ```text
+/// The origin is: Point {
+///     x: 0,
+///     y: 0
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is \
+                            defined in your crate, add `#[derive(Debug)]` or \
+                            manually implement it"]
+#[lang = "debug_trait"]
+pub trait Debug {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for an empty format, `{}`.
+///
+/// `Display` is similar to [`Debug`][debug], but `Display` is for user-facing
+/// output, and so cannot be derived.
+///
+/// [debug]: trait.Debug.html
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Implementing `Display` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl fmt::Display for Point {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         write!(f, "({}, {})", self.x, self.y)
+///     }
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// println!("The origin is: {}", origin);
+/// ```
+#[rustc_on_unimplemented = "`{Self}` cannot be formatted with the default \
+                            formatter; try using `:?` instead if you are using \
+                            a format string"]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Display {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `o` character.
+///
+/// The `Octal` trait should format its output as a number in base-8.
+///
+/// The alternate flag, `#`, adds a `0o` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '52' in octal
+///
+/// assert_eq!(format!("{:o}", x), "52");
+/// assert_eq!(format!("{:#o}", x), "0o52");
+/// ```
+///
+/// Implementing `Octal` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Octal for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///
+///         write!(f, "{:o}", val) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(9);
+///
+/// println!("l as octal is: {:o}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Octal {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `b` character.
+///
+/// The `Binary` trait should format its output as a number in binary.
+///
+/// The alternate flag, `#`, adds a `0b` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '101010' in binary
+///
+/// assert_eq!(format!("{:b}", x), "101010");
+/// assert_eq!(format!("{:#b}", x), "0b101010");
+/// ```
+///
+/// Implementing `Binary` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Binary for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///
+///         write!(f, "{:b}", val) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(107);
+///
+/// println!("l as binary is: {:b}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Binary {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `x` character.
+///
+/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
+/// in lower case.
+///
+/// The alternate flag, `#`, adds a `0x` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '2a' in hex
+///
+/// assert_eq!(format!("{:x}", x), "2a");
+/// assert_eq!(format!("{:#x}", x), "0x2a");
+/// ```
+///
+/// Implementing `LowerHex` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::LowerHex for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///
+///         write!(f, "{:x}", val) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(9);
+///
+/// println!("l as hex is: {:x}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait LowerHex {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `X` character.
+///
+/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
+/// in upper case.
+///
+/// The alternate flag, `#`, adds a `0x` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '2A' in hex
+///
+/// assert_eq!(format!("{:X}", x), "2A");
+/// assert_eq!(format!("{:#X}", x), "0x2A");
+/// ```
+///
+/// Implementing `UpperHex` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::UpperHex for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///
+///         write!(f, "{:X}", val) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(9);
+///
+/// println!("l as hex is: {:X}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait UpperHex {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `p` character.
+///
+/// The `Pointer` trait should format its output as a memory location. This is commonly presented
+/// as hexadecimal.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `&i32`:
+///
+/// ```
+/// let x = &42;
+///
+/// let address = format!("{:p}", x); // this produces something like '0x7f06092ac6d0'
+/// ```
+///
+/// Implementing `Pointer` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Pointer for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         // use `as` to convert to a `*const T`, which implements Pointer, which we can use
+///
+///         write!(f, "{:p}", self as *const Length)
+///     }
+/// }
+///
+/// let l = Length(42);
+///
+/// println!("l is in memory here: {:p}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Pointer {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `e` character.
+///
+/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
+///
+/// assert_eq!(format!("{:e}", x), "4.2e1");
+/// ```
+///
+/// Implementing `LowerExp` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::LowerExp for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///         write!(f, "{}e1", val / 10)
+///     }
+/// }
+///
+/// let l = Length(100);
+///
+/// println!("l in scientific notation is: {:e}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait LowerExp {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// Format trait for the `E` character.
+///
+/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `f32`:
+///
+/// ```
+/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
+///
+/// assert_eq!(format!("{:E}", x), "4.2E1");
+/// ```
+///
+/// Implementing `UpperExp` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::UpperExp for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         let val = self.0;
+///         write!(f, "{}E1", val / 10)
+///     }
+/// }
+///
+/// let l = Length(100);
+///
+/// println!("l in scientific notation is: {:E}", l);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait UpperExp {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, &mut Formatter) -> Result;
+}
+
+/// The `write` function takes an output stream, a precompiled format string,
+/// and a list of arguments. The arguments will be formatted according to the
+/// specified format string into the output stream provided.
+///
+/// # Arguments
+///
+///   * output - the buffer to write output to
+///   * args - the precompiled arguments generated by `format_args!`
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn write(output: &mut Write, args: Arguments) -> Result {
+    let mut formatter = Formatter {
+        flags: 0,
+        width: None,
+        precision: None,
+        buf: output,
+        align: rt::v1::Alignment::Unknown,
+        fill: ' ',
+        args: args.args,
+        curarg: args.args.iter(),
+    };
+
+    let mut pieces = args.pieces.iter();
+
+    match args.fmt {
+        None => {
+            // We can use default formatting parameters for all arguments.
+            for (arg, piece) in args.args.iter().zip(pieces.by_ref()) {
+                formatter.buf.write_str(*piece)?;
+                (arg.formatter)(arg.value, &mut formatter)?;
+            }
+        }
+        Some(fmt) => {
+            // Every spec has a corresponding argument that is preceded by
+            // a string piece.
+            for (arg, piece) in fmt.iter().zip(pieces.by_ref()) {
+                formatter.buf.write_str(*piece)?;
+                formatter.run(arg)?;
+            }
+        }
+    }
+
+    // There can be only one trailing string piece left.
+    match pieces.next() {
+        Some(piece) => {
+            formatter.buf.write_str(*piece)?;
+        }
+        None => {}
+    }
+
+    Ok(())
+}
+
+impl<'a> Formatter<'a> {
+
+    // First up is the collection of functions used to execute a format string
+    // at runtime. This consumes all of the compile-time statics generated by
+    // the format! syntax extension.
+    fn run(&mut self, arg: &rt::v1::Argument) -> Result {
+        // Fill in the format parameters into the formatter
+        self.fill = arg.format.fill;
+        self.align = arg.format.align;
+        self.flags = arg.format.flags;
+        self.width = self.getcount(&arg.format.width);
+        self.precision = self.getcount(&arg.format.precision);
+
+        // Extract the correct argument
+        let value = match arg.position {
+            rt::v1::Position::Next => { *self.curarg.next().unwrap() }
+            rt::v1::Position::At(i) => self.args[i],
+        };
+
+        // Then actually do some printing
+        (value.formatter)(value.value, self)
+    }
+
+    fn getcount(&mut self, cnt: &rt::v1::Count) -> Option<usize> {
+        match *cnt {
+            rt::v1::Count::Is(n) => Some(n),
+            rt::v1::Count::Implied => None,
+            rt::v1::Count::Param(i) => {
+                self.args[i].as_usize()
+            }
+            rt::v1::Count::NextParam => {
+                self.curarg.next().and_then(|arg| arg.as_usize())
+            }
+        }
+    }
+
+    // Helper methods used for padding and processing formatting arguments that
+    // all formatting traits can use.
+
+    /// Performs the correct padding for an integer which has already been
+    /// emitted into a str. The str should *not* contain the sign for the
+    /// integer, that will be added by this method.
+    ///
+    /// # Arguments
+    ///
+    /// * is_nonnegative - whether the original integer was either positive or zero.
+    /// * prefix - if the '#' character (Alternate) is provided, this
+    ///   is the prefix to put in front of the number.
+    /// * buf - the byte array that the number has been formatted into
+    ///
+    /// This function will correctly account for the flags provided as well as
+    /// the minimum width. It will not take precision into account.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pad_integral(&mut self,
+                        is_nonnegative: bool,
+                        prefix: &str,
+                        buf: &str)
+                        -> Result {
+        use char::CharExt;
+
+        let mut width = buf.len();
+
+        let mut sign = None;
+        if !is_nonnegative {
+            sign = Some('-'); width += 1;
+        } else if self.sign_plus() {
+            sign = Some('+'); width += 1;
+        }
+
+        let mut prefixed = false;
+        if self.alternate() {
+            prefixed = true; width += prefix.chars().count();
+        }
+
+        // Writes the sign if it exists, and then the prefix if it was requested
+        let write_prefix = |f: &mut Formatter| {
+            if let Some(c) = sign {
+                f.buf.write_str(unsafe {
+                    str::from_utf8_unchecked(c.encode_utf8().as_slice())
+                })?;
+            }
+            if prefixed { f.buf.write_str(prefix) }
+            else { Ok(()) }
+        };
+
+        // The `width` field is more of a `min-width` parameter at this point.
+        match self.width {
+            // If there's no minimum length requirements then we can just
+            // write the bytes.
+            None => {
+                write_prefix(self)?; self.buf.write_str(buf)
+            }
+            // Check if we're over the minimum width, if so then we can also
+            // just write the bytes.
+            Some(min) if width >= min => {
+                write_prefix(self)?; self.buf.write_str(buf)
+            }
+            // The sign and prefix goes before the padding if the fill character
+            // is zero
+            Some(min) if self.sign_aware_zero_pad() => {
+                self.fill = '0';
+                write_prefix(self)?;
+                self.with_padding(min - width, rt::v1::Alignment::Right, |f| {
+                    f.buf.write_str(buf)
+                })
+            }
+            // Otherwise, the sign and prefix goes after the padding
+            Some(min) => {
+                self.with_padding(min - width, rt::v1::Alignment::Right, |f| {
+                    write_prefix(f)?; f.buf.write_str(buf)
+                })
+            }
+        }
+    }
+
+    /// This function takes a string slice and emits it to the internal buffer
+    /// after applying the relevant formatting flags specified. The flags
+    /// recognized for generic strings are:
+    ///
+    /// * width - the minimum width of what to emit
+    /// * fill/align - what to emit and where to emit it if the string
+    ///                provided needs to be padded
+    /// * precision - the maximum length to emit, the string is truncated if it
+    ///               is longer than this length
+    ///
+    /// Notably this function ignored the `flag` parameters
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pad(&mut self, s: &str) -> Result {
+        // Make sure there's a fast path up front
+        if self.width.is_none() && self.precision.is_none() {
+            return self.buf.write_str(s);
+        }
+        // The `precision` field can be interpreted as a `max-width` for the
+        // string being formatted
+        if let Some(max) = self.precision {
+            // If there's a maximum width and our string is longer than
+            // that, then we must always have truncation. This is the only
+            // case where the maximum length will matter.
+            if let Some((i, _)) = s.char_indices().skip(max).next() {
+                return self.buf.write_str(&s[..i])
+            }
+        }
+        // The `width` field is more of a `min-width` parameter at this point.
+        match self.width {
+            // If we're under the maximum length, and there's no minimum length
+            // requirements, then we can just emit the string
+            None => self.buf.write_str(s),
+            // If we're under the maximum width, check if we're over the minimum
+            // width, if so it's as easy as just emitting the string.
+            Some(width) if s.chars().count() >= width => {
+                self.buf.write_str(s)
+            }
+            // If we're under both the maximum and the minimum width, then fill
+            // up the minimum width with the specified string + some alignment.
+            Some(width) => {
+                let align = rt::v1::Alignment::Left;
+                self.with_padding(width - s.chars().count(), align, |me| {
+                    me.buf.write_str(s)
+                })
+            }
+        }
+    }
+
+    /// Runs a callback, emitting the correct padding either before or
+    /// afterwards depending on whether right or left alignment is requested.
+    fn with_padding<F>(&mut self, padding: usize, default: rt::v1::Alignment,
+                       f: F) -> Result
+        where F: FnOnce(&mut Formatter) -> Result,
+    {
+        use char::CharExt;
+        let align = match self.align {
+            rt::v1::Alignment::Unknown => default,
+            _ => self.align
+        };
+
+        let (pre_pad, post_pad) = match align {
+            rt::v1::Alignment::Left => (0, padding),
+            rt::v1::Alignment::Right |
+            rt::v1::Alignment::Unknown => (padding, 0),
+            rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
+        };
+
+        let fill = self.fill.encode_utf8();
+        let fill = unsafe {
+            str::from_utf8_unchecked(fill.as_slice())
+        };
+
+        for _ in 0..pre_pad {
+            self.buf.write_str(fill)?;
+        }
+
+        f(self)?;
+
+        for _ in 0..post_pad {
+            self.buf.write_str(fill)?;
+        }
+
+        Ok(())
+    }
+
+    /// Takes the formatted parts and applies the padding.
+    /// Assumes that the caller already has rendered the parts with required precision,
+    /// so that `self.precision` can be ignored.
+    fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
+        if let Some(mut width) = self.width {
+            // for the sign-aware zero padding, we render the sign first and
+            // behave as if we had no sign from the beginning.
+            let mut formatted = formatted.clone();
+            let mut align = self.align;
+            let old_fill = self.fill;
+            if self.sign_aware_zero_pad() {
+                // a sign always goes first
+                let sign = unsafe { str::from_utf8_unchecked(formatted.sign) };
+                self.buf.write_str(sign)?;
+
+                // remove the sign from the formatted parts
+                formatted.sign = b"";
+                width = if width < sign.len() { 0 } else { width - sign.len() };
+                align = rt::v1::Alignment::Right;
+                self.fill = '0';
+            }
+
+            // remaining parts go through the ordinary padding process.
+            let len = formatted.len();
+            let ret = if width <= len { // no padding
+                self.write_formatted_parts(&formatted)
+            } else {
+                self.with_padding(width - len, align, |f| {
+                    f.write_formatted_parts(&formatted)
+                })
+            };
+            self.fill = old_fill;
+            ret
+        } else {
+            // this is the common case and we take a shortcut
+            self.write_formatted_parts(formatted)
+        }
+    }
+
+    fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
+        fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
+            buf.write_str(unsafe { str::from_utf8_unchecked(s) })
+        }
+
+        if !formatted.sign.is_empty() {
+            write_bytes(self.buf, formatted.sign)?;
+        }
+        for part in formatted.parts {
+            match *part {
+                flt2dec::Part::Zero(mut nzeroes) => {
+                    const ZEROES: &'static str = // 64 zeroes
+                        "0000000000000000000000000000000000000000000000000000000000000000";
+                    while nzeroes > ZEROES.len() {
+                        self.buf.write_str(ZEROES)?;
+                        nzeroes -= ZEROES.len();
+                    }
+                    if nzeroes > 0 {
+                        self.buf.write_str(&ZEROES[..nzeroes])?;
+                    }
+                }
+                flt2dec::Part::Num(mut v) => {
+                    let mut s = [0; 5];
+                    let len = part.len();
+                    for c in s[..len].iter_mut().rev() {
+                        *c = b'0' + (v % 10) as u8;
+                        v /= 10;
+                    }
+                    write_bytes(self.buf, &s[..len])?;
+                }
+                flt2dec::Part::Copy(buf) => {
+                    write_bytes(self.buf, buf)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Writes some data to the underlying buffer contained within this
+    /// formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn write_str(&mut self, data: &str) -> Result {
+        self.buf.write_str(data)
+    }
+
+    /// Writes some formatted information into this instance
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
+        write(self.buf, fmt)
+    }
+
+    /// Flags for formatting (packed version of rt::Flag)
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn flags(&self) -> u32 { self.flags }
+
+    /// Character used as 'fill' whenever there is alignment
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn fill(&self) -> char { self.fill }
+
+    /// Flag indicating what form of alignment was requested
+    #[unstable(feature = "fmt_flags_align", reason = "method was just created",
+               issue = "27726")]
+    pub fn align(&self) -> Alignment {
+        match self.align {
+            rt::v1::Alignment::Left => Alignment::Left,
+            rt::v1::Alignment::Right => Alignment::Right,
+            rt::v1::Alignment::Center => Alignment::Center,
+            rt::v1::Alignment::Unknown => Alignment::Unknown,
+        }
+    }
+
+    /// Optionally specified integer width that the output should be
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn width(&self) -> Option<usize> { self.width }
+
+    /// Optionally specified precision for numeric types
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn precision(&self) -> Option<usize> { self.precision }
+
+    /// Determines if the `+` flag was specified.
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_plus(&self) -> bool { self.flags & (1 << FlagV1::SignPlus as u32) != 0 }
+
+    /// Determines if the `-` flag was specified.
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_minus(&self) -> bool { self.flags & (1 << FlagV1::SignMinus as u32) != 0 }
+
+    /// Determines if the `#` flag was specified.
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn alternate(&self) -> bool { self.flags & (1 << FlagV1::Alternate as u32) != 0 }
+
+    /// Determines if the `0` flag was specified.
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_aware_zero_pad(&self) -> bool {
+        self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
+    }
+
+    /// Creates a `DebugStruct` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for structs.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo {
+    ///     bar: i32,
+    ///     baz: String,
+    /// }
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_struct("Foo")
+    ///             .field("bar", &self.bar)
+    ///             .field("baz", &self.baz)
+    ///             .finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "Foo { bar: 10, baz: "Hello World" }"
+    /// println!("{:?}", Foo { bar: 10, baz: "Hello World".to_string() });
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    #[inline]
+    pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
+        builders::debug_struct_new(self, name)
+    }
+
+    /// Creates a `DebugTuple` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for tuple structs.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32, String);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_tuple("Foo")
+    ///             .field(&self.0)
+    ///             .field(&self.1)
+    ///             .finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "Foo(10, "Hello World")"
+    /// println!("{:?}", Foo(10, "Hello World".to_string()));
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    #[inline]
+    pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
+        builders::debug_tuple_new(self, name)
+    }
+
+    /// Creates a `DebugList` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for list-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<i32>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_list().entries(self.0.iter()).finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "[10, 11]"
+    /// println!("{:?}", Foo(vec![10, 11]));
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    #[inline]
+    pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
+        builders::debug_list_new(self)
+    }
+
+    /// Creates a `DebugSet` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for set-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<i32>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_set().entries(self.0.iter()).finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "{10, 11}"
+    /// println!("{:?}", Foo(vec![10, 11]));
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    #[inline]
+    pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
+        builders::debug_set_new(self)
+    }
+
+    /// Creates a `DebugMap` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for map-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<(String, i32)>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "{"A": 10, "B": 11}"
+    /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    #[inline]
+    pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
+        builders::debug_map_new(self)
+    }
+}
+
+#[stable(since = "1.2.0", feature = "formatter_write")]
+impl<'a> Write for Formatter<'a> {
+    fn write_str(&mut self, s: &str) -> Result {
+        self.buf.write_str(s)
+    }
+
+    fn write_char(&mut self, c: char) -> Result {
+        self.buf.write_char(c)
+    }
+
+    fn write_fmt(&mut self, args: Arguments) -> Result {
+        write(self.buf, args)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Display::fmt("an error occurred when formatting an argument", f)
+    }
+}
+
+// Implementations of the core formatting traits
+
+macro_rules! fmt_refs {
+    ($($tr:ident),*) => {
+        $(
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, T: ?Sized + $tr> $tr for &'a T {
+            fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
+        }
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, T: ?Sized + $tr> $tr for &'a mut T {
+            fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
+        }
+        )*
+    }
+}
+
+fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for bool {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Display::fmt(self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for bool {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Display::fmt(if *self { "true" } else { "false" }, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for str {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.write_char('"')?;
+        let mut from = 0;
+        for (i, c) in self.char_indices() {
+            let esc = c.escape_default();
+            // If char needs escaping, flush backlog so far and write, else skip
+            if esc.size_hint() != (1, Some(1)) {
+                f.write_str(&self[from..i])?;
+                for c in esc {
+                    f.write_char(c)?;
+                }
+                from = i + c.len_utf8();
+            }
+        }
+        f.write_str(&self[from..])?;
+        f.write_char('"')
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for str {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.pad(self)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for char {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.write_char('\'')?;
+        for c in self.escape_default() {
+            f.write_char(c)?
+        }
+        f.write_char('\'')
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for char {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        if f.width.is_none() && f.precision.is_none() {
+            f.write_char(*self)
+        } else {
+            f.pad(unsafe {
+                str::from_utf8_unchecked(self.encode_utf8().as_slice())
+            })
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for *const T {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        let old_width = f.width;
+        let old_flags = f.flags;
+
+        // The alternate flag is already treated by LowerHex as being special-
+        // it denotes whether to prefix with 0x. We use it to work out whether
+        // or not to zero extend, and then unconditionally set it to get the
+        // prefix.
+        if f.alternate() {
+            f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
+
+            if let None = f.width {
+                f.width = Some(((mem::size_of::<usize>() * 8) / 4) + 2);
+            }
+        }
+        f.flags |= 1 << (FlagV1::Alternate as u32);
+
+        let ret = LowerHex::fmt(&(*self as *const () as usize), f);
+
+        f.width = old_width;
+        f.flags = old_flags;
+
+        ret
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for *mut T {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Pointer::fmt(&(*self as *const T), f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: ?Sized> Pointer for &'a T {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Pointer::fmt(&(*self as *const T), f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: ?Sized> Pointer for &'a mut T {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Pointer::fmt(&(&**self as *const T), f)
+    }
+}
+
+// Common code of floating point Debug and Display.
+fn float_to_decimal_common<T>(fmt: &mut Formatter, num: &T, negative_zero: bool) -> Result
+    where T: flt2dec::DecodableFloat
+{
+    let force_sign = fmt.sign_plus();
+    let sign = match (force_sign, negative_zero) {
+        (false, false) => flt2dec::Sign::Minus,
+        (false, true)  => flt2dec::Sign::MinusRaw,
+        (true,  false) => flt2dec::Sign::MinusPlus,
+        (true,  true)  => flt2dec::Sign::MinusPlusRaw,
+    };
+
+    let mut buf = [0; 1024]; // enough for f32 and f64
+    let mut parts = [flt2dec::Part::Zero(0); 16];
+    let formatted = if let Some(precision) = fmt.precision {
+        flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact, *num, sign,
+                                    precision, false, &mut buf, &mut parts)
+    } else {
+        flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
+                                 0, false, &mut buf, &mut parts)
+    };
+    fmt.pad_formatted_parts(&formatted)
+}
+
+// Common code of floating point LowerExp and UpperExp.
+fn float_to_exponential_common<T>(fmt: &mut Formatter, num: &T, upper: bool) -> Result
+    where T: flt2dec::DecodableFloat
+{
+    let force_sign = fmt.sign_plus();
+    let sign = match force_sign {
+        false => flt2dec::Sign::Minus,
+        true  => flt2dec::Sign::MinusPlus,
+    };
+
+    let mut buf = [0; 1024]; // enough for f32 and f64
+    let mut parts = [flt2dec::Part::Zero(0); 16];
+    let formatted = if let Some(precision) = fmt.precision {
+        // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
+        flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact, *num, sign,
+                                  precision + 1, upper, &mut buf, &mut parts)
+    } else {
+        flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
+                                     (0, 0), upper, &mut buf, &mut parts)
+    };
+    fmt.pad_formatted_parts(&formatted)
+}
+
+macro_rules! floating { ($ty:ident) => {
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl Debug for $ty {
+        fn fmt(&self, fmt: &mut Formatter) -> Result {
+            float_to_decimal_common(fmt, self, true)
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl Display for $ty {
+        fn fmt(&self, fmt: &mut Formatter) -> Result {
+            float_to_decimal_common(fmt, self, false)
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl LowerExp for $ty {
+        fn fmt(&self, fmt: &mut Formatter) -> Result {
+            float_to_exponential_common(fmt, self, false)
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl UpperExp for $ty {
+        fn fmt(&self, fmt: &mut Formatter) -> Result {
+            float_to_exponential_common(fmt, self, true)
+        }
+    }
+} }
+floating! { f32 }
+floating! { f64 }
+
+// Implementation of Display/Debug for various core types
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Debug for *const T {
+    fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Debug for *mut T {
+    fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
+}
+
+macro_rules! peel {
+    ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
+}
+
+macro_rules! tuple {
+    () => ();
+    ( $($name:ident,)+ ) => (
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<$($name:Debug),*> Debug for ($($name,)*) {
+            #[allow(non_snake_case, unused_assignments, deprecated)]
+            fn fmt(&self, f: &mut Formatter) -> Result {
+                let mut builder = f.debug_tuple("");
+                let ($(ref $name,)*) = *self;
+                $(
+                    builder.field($name);
+                )*
+
+                builder.finish()
+            }
+        }
+        peel! { $($name,)* }
+    )
+}
+
+tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Debug> Debug for [T] {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for () {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.pad("()")
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Debug for PhantomData<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.pad("PhantomData")
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Copy + Debug> Debug for Cell<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.debug_struct("Cell")
+            .field("value", &self.get())
+            .finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Debug> Debug for RefCell<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        match self.borrow_state() {
+            BorrowState::Unused | BorrowState::Reading => {
+                f.debug_struct("RefCell")
+                    .field("value", &self.borrow())
+                    .finish()
+            }
+            BorrowState::Writing => {
+                f.debug_struct("RefCell")
+                    .field("value", &"<borrowed>")
+                    .finish()
+            }
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'b, T: ?Sized + Debug> Debug for Ref<'b, T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Debug::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'b, T: ?Sized + Debug> Debug for RefMut<'b, T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        Debug::fmt(&*(self.deref()), f)
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: ?Sized + Debug> Debug for UnsafeCell<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result {
+        f.pad("UnsafeCell")
+    }
+}
+
+// If you expected tests to be here, look instead at the run-pass/ifmt.rs test,
+// it's a lot easier than creating all of the rt::Piece structures here.