add libcore from 2016-04-11 nightly

1 files changed, 25 insertions, 0 deletions

diff --git a/libcore/num/flt2dec/estimator.rs b/libcore/num/flt2dec/estimator.rs
new file mode 100644
index 0000000..d42e05a
--- /dev/null
+++ b/libcore/num/flt2dec/estimator.rs
@@ -0,0 +1,25 @@
+// Copyright 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.
+
+//! The exponent estimator.
+
+/// Finds `k_0` such that `10^(k_0-1) < mant * 2^exp <= 10^(k_0+1)`.
+///
+/// This is used to approximate `k = ceil(log_10 (mant * 2^exp))`;
+/// the true `k` is either `k_0` or `k_0+1`.
+#[doc(hidden)]
+pub fn estimate_scaling_factor(mant: u64, exp: i16) -> i16 {
+    // 2^(nbits-1) < mant <= 2^nbits if mant > 0
+    let nbits = 64 - (mant - 1).leading_zeros() as i64;
+    // 1292913986 = floor(2^32 * log_10 2)
+    // therefore this always underestimates (or is exact), but not much.
+    (((nbits + exp as i64) * 1292913986) >> 32) as i16
+}
+