// Protocol Buffers - Google's data interchange format
// Copyright 2014 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// Fast memory copying and comparison routines.
// strings::fastmemcmp_inlined() replaces memcmp()
// strings::memcpy_inlined() replaces memcpy()
// strings::memeq(a, b, n) replaces memcmp(a, b, n) == 0
//
// strings::*_inlined() routines are inline versions of the
// routines exported by this module. Sometimes using the inlined
// versions is faster. Measure before using the inlined versions.
//
// Performance measurement:
// strings::fastmemcmp_inlined
// Analysis: memcmp, fastmemcmp_inlined, fastmemcmp
// 2012-01-30
#ifndef GOOGLE_PROTOBUF_STUBS_FASTMEM_H_
#define GOOGLE_PROTOBUF_STUBS_FASTMEM_H_
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <google/protobuf/stubs/common.h>
namespace google {
namespace protobuf {
namespace internal {
// Return true if the n bytes at a equal the n bytes at b.
// The regions are allowed to overlap.
//
// The performance is similar to the performance memcmp(), but faster for
// moderately-sized inputs, or inputs that share a common prefix and differ
// somewhere in their last 8 bytes. Further optimizations can be added later
// if it makes sense to do so.:w
inline bool memeq(const char* a, const char* b, size_t n) {
size_t n_rounded_down = n & ~static_cast<size_t>(7);
if (GOOGLE_PREDICT_FALSE(n_rounded_down == 0)) { // n <= 7
return memcmp(a, b, n) == 0;
}
// n >= 8
uint64 u = GOOGLE_UNALIGNED_LOAD64(a) ^ GOOGLE_UNALIGNED_LOAD64(b);
uint64 v = GOOGLE_UNALIGNED_LOAD64(a + n - 8) ^ GOOGLE_UNALIGNED_LOAD64(b + n - 8);
if ((u | v) != 0) { // The first or last 8 bytes differ.
return false;
}
a += 8;
b += 8;
n = n_rounded_down - 8;
if (n > 128) {
// As of 2012, memcmp on x86-64 uses a big unrolled loop with SSE2
// instructions, and while we could try to do something faster, it
// doesn't seem worth pursuing.
return memcmp(a, b, n) == 0;
}
for (; n >= 16; n -= 16) {
uint64 x = GOOGLE_UNALIGNED_LOAD64(a) ^ GOOGLE_UNALIGNED_LOAD64(b);
uint64 y = GOOGLE_UNALIGNED_LOAD64(a + 8) ^ GOOGLE_UNALIGNED_LOAD64(b + 8);
if ((x | y) != 0) {
return false;
}
a += 16;
b += 16;
}
// n must be 0 or 8 now because it was a multiple of 8 at the top of the loop.
return n == 0 || GOOGLE_UNALIGNED_LOAD64(a) == GOOGLE_UNALIGNED_LOAD64(b);
}
inline int fastmemcmp_inlined(const char *a, const char *b, size_t n) {
if (n >= 64) {
return memcmp(a, b, n);
}
const char* a_limit = a + n;
while (a + sizeof(uint64) <= a_limit &&
GOOGLE_UNALIGNED_LOAD64(a) == GOOGLE_UNALIGNED_LOAD64(b)) {
a += sizeof(uint64);
b += sizeof(uint64);
}
if (a + sizeof(uint32) <= a_limit &&
GOOGLE_UNALIGNED_LOAD32(a) == GOOGLE_UNALIGNED_LOAD32(b)) {
a += sizeof(uint32);
b += sizeof(uint32);
}
while (a < a_limit) {
int d =
static_cast<int>(static_cast<uint32>(*a++) - static_cast<uint32>(*b++));
if (d) return d;
}
return 0;
}
// The standard memcpy operation is slow for variable small sizes.
// This implementation inlines the optimal realization for sizes 1 to 16.
// To avoid code bloat don't use it in case of not performance-critical spots,
// nor when you don't expect very frequent values of size <= 16.
inline void memcpy_inlined(char *dst, const char *src, size_t size) {
// Compiler inlines code with minimal amount of data movement when third
// parameter of memcpy is a constant.
switch (size) {
case 1: memcpy(dst, src, 1); break;
case 2: memcpy(dst, src, 2); break;
case 3: memcpy(dst, src, 3); break;
case 4: memcpy(dst, src, 4); break;
case 5: memcpy(dst, src, 5); break;
case 6: memcpy(dst, src, 6); break;
case 7: memcpy(dst, src, 7); break;
case 8: memcpy(dst, src, 8); break;
case 9: memcpy(dst, src, 9); break;
case 10: memcpy(dst, src, 10); break;
case 11: memcpy(dst, src, 11); break;
case 12: memcpy(dst, src, 12); break;
case 13: memcpy(dst, src, 13); break;
case 14: memcpy(dst, src, 14); break;
case 15: memcpy(dst, src, 15); break;
case 16: memcpy(dst, src, 16); break;
default: memcpy(dst, src, size); break;
}
}
} // namespace internal
} // namespace protobuf
} // namespace google
#endif // GOOGLE_PROTOBUF_STUBS_FASTMEM_H_
