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Inline branch-less VarintSize32/VarintSize64 implementations.

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This commit is contained in:
Chris Kennelly 2017-02-02 16:33:02 -08:00
parent 39756643df
commit 36f68e02d5
2 changed files with 17 additions and 26 deletions
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19
src/google/protobuf/io/coded_stream.cc
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@ -816,25 +816,6 @@ bool CodedOutputStream::Refresh() {
}
}
size_t CodedOutputStream::VarintSize32Fallback(uint32 value) {
// This computes floor(log2(value)) / 7 + 1
// Use an explicit multiplication to implement the divide of
// a number in the 1..31 range.
GOOGLE_DCHECK_NE(0, value); // This is enforced by our caller.
uint32 log2value = Bits::Log2FloorNonZero(value);
return static_cast<size_t>((log2value * 9 + 73) / 64);
}
size_t CodedOutputStream::VarintSize64(uint64 value) {
// This computes value == 0 ? 1 : floor(log2(value)) / 7 + 1
// Use an explicit multiplication to implement the divide of
// a number in the 1..63 range.
// Explicit OR 0x1 to avoid calling clz(0), which is undefined.
uint32 log2value = Bits::Log2FloorNonZero64(value | 0x1);
return static_cast<size_t>((log2value * 9 + 73) / 64);
}
uint8* CodedOutputStream::WriteStringWithSizeToArray(const string& str,
uint8* target) {
GOOGLE_DCHECK_LE(str.size(), kuint32max);

24
src/google/protobuf/io/coded_stream.h
View File

@ -903,8 +903,6 @@ class LIBPROTOBUF_EXPORT CodedOutputStream {
void WriteVarint32SlowPath(uint32 value);
void WriteVarint64SlowPath(uint64 value);
static size_t VarintSize32Fallback(uint32 value);
// See above. Other projects may use "friend" to allow them to call this.
// Requires: no protocol buffer serialization in progress.
friend void ::google::protobuf::internal::MapTestForceDeterministic();
@ -1292,11 +1290,23 @@ inline uint8* CodedOutputStream::WriteTagToArray(
}
inline size_t CodedOutputStream::VarintSize32(uint32 value) {
if (value < (1 << 7)) {
return 1;
} else {
return VarintSize32Fallback(value);
}
// This computes value == 0 ? 1 : floor(log2(value)) / 7 + 1
// Use an explicit multiplication to implement the divide of
// a number in the 1..31 range.
// Explicit OR 0x1 to avoid calling Bits::Log2FloorNonZero(0), which is
// undefined.
uint32 log2value = Bits::Log2FloorNonZero(value | 0x1);
return static_cast<size_t>((log2value * 9 + 73) / 64);
}
inline size_t CodedOutputStream::VarintSize64(uint64 value) {
// This computes value == 0 ? 1 : floor(log2(value)) / 7 + 1
// Use an explicit multiplication to implement the divide of
// a number in the 1..63 range.
// Explicit OR 0x1 to avoid calling Bits::Log2FloorNonZero(0), which is
// undefined.
uint32 log2value = Bits::Log2FloorNonZero64(value | 0x1);
return static_cast<size_t>((log2value * 9 + 73) / 64);
}
inline size_t CodedOutputStream::VarintSize32SignExtended(int32 value) {