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Diffstat (limited to 'src/google/protobuf/stubs/fastmem.h')
| -rw-r--r-- | src/google/protobuf/stubs/fastmem.h | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/src/google/protobuf/stubs/fastmem.h b/src/google/protobuf/stubs/fastmem.h new file mode 100644 index 00000000..e553f142 --- /dev/null +++ b/src/google/protobuf/stubs/fastmem.h @@ -0,0 +1,153 @@ +// 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 <stdint.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<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_ |