From 151b0a7766a115103416e48a6c9e0bf5acc2a5aa Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan@engelbrecht.com>
Date: Wed, 6 Mar 2024 12:49:31 +0100
Subject: Add WriteMeasuredVarUInt to avoid measuring ints twice before writing
 (#665)

Avoid double resize of buffer in CbWriter::SetName and CbWriter::AddBinary
Add WriteMeasuredVarUInt to avoid measuring ints twice before writing
---
 src/zencore/compactbinarybuilder.cpp | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

(limited to 'src/zencore/compactbinarybuilder.cpp')

diff --git a/src/zencore/compactbinarybuilder.cpp b/src/zencore/compactbinarybuilder.cpp
index 5c08d2e6e..3331291ce 100644
--- a/src/zencore/compactbinarybuilder.cpp
+++ b/src/zencore/compactbinarybuilder.cpp
@@ -221,12 +221,11 @@ CbWriter::SetName(const std::string_view Name)
 	State.Flags |= StateFlags::Name;
 	const uint32_t NameLenByteCount = MeasureVarUInt(uint32_t(Name.size()));
 	const int64_t  NameLenOffset	= Data.size();
-	Data.resize(NameLenOffset + NameLenByteCount);
+	Data.resize(NameLenOffset + NameLenByteCount + Name.size());
 
-	WriteVarUInt(uint64_t(Name.size()), Data.data() + NameLenOffset);
+	WriteMeasuredVarUInt(uint64_t(Name.size()), NameLenByteCount, Data.data() + NameLenOffset);
 
-	const uint8_t* NamePtr = reinterpret_cast<const uint8_t*>(Name.data());
-	Data.insert(Data.end(), NamePtr, NamePtr + Name.size());
+	memcpy(Data.data() + NameLenOffset + NameLenByteCount, Name.data(), Name.size());
 	return *this;
 }
 
@@ -341,7 +340,7 @@ CbWriter::EndObject()
 	const uint64_t Size			 = uint64_t(Data.size() - PayloadOffset);
 	const uint32_t SizeByteCount = MeasureVarUInt(Size);
 	Data.insert(Data.begin() + PayloadOffset, SizeByteCount, 0);
-	WriteVarUInt(Size, Data.data() + PayloadOffset);
+	WriteMeasuredVarUInt(Size, SizeByteCount, Data.data() + PayloadOffset);
 
 	EndField(bUniform ? CbFieldType::UniformObject : CbFieldType::Object);
 }
@@ -400,8 +399,8 @@ CbWriter::EndArray()
 	const uint64_t Size			  = uint64_t(Data.size() - PayloadOffset) + CountByteCount;
 	const uint32_t SizeByteCount  = MeasureVarUInt(Size);
 	Data.insert(Data.begin() + PayloadOffset, SizeByteCount + CountByteCount, 0);
-	WriteVarUInt(Size, Data.data() + PayloadOffset);
-	WriteVarUInt(Count, Data.data() + PayloadOffset + SizeByteCount);
+	WriteMeasuredVarUInt(Size, SizeByteCount, Data.data() + PayloadOffset);
+	WriteMeasuredVarUInt(Count, CountByteCount, Data.data() + PayloadOffset + SizeByteCount);
 
 	EndField(bUniform ? CbFieldType::UniformArray : CbFieldType::Array);
 }
@@ -429,13 +428,13 @@ CbWriter::AddNull()
 void
 CbWriter::AddBinary(const void* const Value, const uint64_t Size)
 {
-	const size_t SizeByteCount = MeasureVarUInt(Size);
+	const uint32_t SizeByteCount = MeasureVarUInt(Size);
 	Data.reserve(Data.size() + 1 + SizeByteCount + Size);
 	BeginField();
 	const size_t SizeOffset = Data.size();
-	Data.resize(Data.size() + SizeByteCount);
-	WriteVarUInt(Size, Data.data() + SizeOffset);
-	Data.insert(Data.end(), static_cast<const uint8_t*>(Value), static_cast<const uint8_t*>(Value) + Size);
+	Data.resize(Data.size() + SizeByteCount + Size);
+	WriteMeasuredVarUInt(Size, SizeByteCount, Data.data() + SizeOffset);
+	memcpy(Data.data() + SizeOffset + SizeByteCount, Value, Size);
 	EndField(CbFieldType::Binary);
 }
 
@@ -468,7 +467,7 @@ CbWriter::AddString(const std::string_view Value)
 	Data.resize(Offset + SizeByteCount + Size);
 
 	uint8_t* StringData = Data.data() + Offset;
-	WriteVarUInt(Size, StringData);
+	WriteMeasuredVarUInt(Size, SizeByteCount, StringData);
 	StringData += SizeByteCount;
 	if (Size > 0)
 	{
@@ -489,7 +488,7 @@ CbWriter::AddString(const std::wstring_view Value)
 	const int64_t  Offset		 = Data.size();
 	Data.resize(Offset + SizeByteCount + Size);
 	uint8_t* StringData = Data.data() + Offset;
-	WriteVarUInt(Size, StringData);
+	WriteMeasuredVarUInt(Size, SizeByteCount, StringData);
 	StringData += SizeByteCount;
 	if (Size > 0)
 	{
@@ -511,7 +510,7 @@ CbWriter::AddInteger(const int32_t Value)
 	const uint32_t MagnitudeByteCount = MeasureVarUInt(Magnitude);
 	const int64_t  Offset			  = Data.size();
 	Data.resize(Offset + MagnitudeByteCount);
-	WriteVarUInt(Magnitude, Data.data() + Offset);
+	WriteMeasuredVarUInt(Magnitude, MagnitudeByteCount, Data.data() + Offset);
 	EndField(CbFieldType::IntegerNegative);
 }
 
@@ -526,7 +525,7 @@ CbWriter::AddInteger(const int64_t Value)
 	const uint64_t Magnitude		  = ~uint64_t(Value);
 	const uint32_t MagnitudeByteCount = MeasureVarUInt(Magnitude);
 	const uint64_t Offset			  = AddUninitialized(Data, MagnitudeByteCount);
-	WriteVarUInt(Magnitude, Data.data() + Offset);
+	WriteMeasuredVarUInt(Magnitude, MagnitudeByteCount, Data.data() + Offset);
 	EndField(CbFieldType::IntegerNegative);
 }
 
@@ -537,7 +536,7 @@ CbWriter::AddInteger(const uint32_t Value)
 	BeginField();
 	const uint32_t ValueByteCount = MeasureVarUInt(Value);
 	const uint64_t Offset		  = AddUninitialized(Data, ValueByteCount);
-	WriteVarUInt(Value, Data.data() + Offset);
+	WriteMeasuredVarUInt(Value, ValueByteCount, Data.data() + Offset);
 	EndField(CbFieldType::IntegerPositive);
 }
 
@@ -548,7 +547,7 @@ CbWriter::AddInteger(const uint64_t Value)
 	BeginField();
 	const uint32_t ValueByteCount = MeasureVarUInt(Value);
 	const uint64_t Offset		  = AddUninitialized(Data, ValueByteCount);
-	WriteVarUInt(Value, Data.data() + Offset);
+	WriteMeasuredVarUInt(Value, ValueByteCount, Data.data() + Offset);
 	EndField(CbFieldType::IntegerPositive);
 }
 
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