// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/strings/internal/memutil.h"
#include <algorithm>
#include <cstdlib>
#include "benchmark/benchmark.h"
#include "absl/strings/ascii.h"
// We fill the haystack with aaaaaaaaaaaaaaaaaa...aaaab.
// That gives us:
// - an easy search: 'b'
// - a medium search: 'ab'. That means every letter is a possible match.
// - a pathological search: 'aaaaaa.......aaaaab' (half as many a's as haytack)
// We benchmark case-sensitive and case-insensitive versions of
// three memmem implementations:
// - memmem() from memutil.h
// - search() from STL
// - memmatch(), a custom implementation using memchr and memcmp.
// Here are sample results:
//
// Run on (12 X 3800 MHz CPU s)
// CPU Caches:
// L1 Data 32K (x6)
// L1 Instruction 32K (x6)
// L2 Unified 256K (x6)
// L3 Unified 15360K (x1)
// ----------------------------------------------------------------
// Benchmark Time CPU Iterations
// ----------------------------------------------------------------
// BM_Memmem 3583 ns 3582 ns 196469 2.59966GB/s
// BM_MemmemMedium 13743 ns 13742 ns 50901 693.986MB/s
// BM_MemmemPathological 13695030 ns 13693977 ns 51 713.133kB/s
// BM_Memcasemem 3299 ns 3299 ns 212942 2.82309GB/s
// BM_MemcasememMedium 16407 ns 16406 ns 42170 581.309MB/s
// BM_MemcasememPathological 17267745 ns 17266030 ns 41 565.598kB/s
// BM_Search 1610 ns 1609 ns 431321 5.78672GB/s
// BM_SearchMedium 11111 ns 11110 ns 63001 858.414MB/s
// BM_SearchPathological 12117390 ns 12116397 ns 58 805.984kB/s
// BM_Searchcase 3081 ns 3081 ns 229949 3.02313GB/s
// BM_SearchcaseMedium 16003 ns 16001 ns 44170 595.998MB/s
// BM_SearchcasePathological 15823413 ns 15821909 ns 44 617.222kB/s
// BM_Memmatch 197 ns 197 ns 3584225 47.2951GB/s
// BM_MemmatchMedium 52333 ns 52329 ns 13280 182.244MB/s
// BM_MemmatchPathological 659799 ns 659727 ns 1058 14.4556MB/s
// BM_Memcasematch 5460 ns 5460 ns 127606 1.70586GB/s
// BM_MemcasematchMedium 32861 ns 32857 ns 21258 290.248MB/s
// BM_MemcasematchPathological 15154243 ns 15153089 ns 46 644.464kB/s
// BM_MemmemStartup 5 ns 5 ns 150821500
// BM_SearchStartup 5 ns 5 ns 150644203
// BM_MemmatchStartup 7 ns 7 ns 97068802
//
// Conclusions:
//
// The following recommendations are based on the sample results above. However,
// we have found that the performance of STL search can vary significantly
// depending on compiler and standard library implementation. We recommend you
// run the benchmarks for yourself on relevant platforms.
//
// If you need case-insensitive, STL search is slightly better than memmem for
// all cases.
//
// Case-sensitive is more subtle:
// Custom memmatch is _very_ fast at scanning, so if you have very few possible
// matches in your haystack, that's the way to go. Performance drops
// significantly with more matches.
//
// STL search is slightly faster than memmem in the medium and pathological
// benchmarks. However, the performance of memmem is currently more dependable
// across platforms and build configurations.
namespace {
constexpr int kHaystackSize = 10000;
constexpr int64_t kHaystackSize64 = kHaystackSize;
const char* MakeHaystack() {
char* haystack = new char[kHaystackSize];
for (int i = 0; i < kHaystackSize - 1; ++i) haystack[i] = 'a';
haystack[kHaystackSize - 1] = 'b';
return haystack;
}
const char* const kHaystack = MakeHaystack();
void BM_Memmem(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memmem(kHaystack, kHaystackSize, "b", 1));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Memmem);
void BM_MemmemMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memmem(kHaystack, kHaystackSize, "ab", 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemmemMedium);
void BM_MemmemPathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(absl::strings_internal::memmem(
kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
kHaystackSize - kHaystackSize / 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemmemPathological);
void BM_Memcasemem(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memcasemem(kHaystack, kHaystackSize, "b", 1));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Memcasemem);
void BM_MemcasememMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memcasemem(kHaystack, kHaystackSize, "ab", 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemcasememMedium);
void BM_MemcasememPathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(absl::strings_internal::memcasemem(
kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
kHaystackSize - kHaystackSize / 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemcasememPathological);
bool case_eq(const char a, const char b) {
return absl::ascii_tolower(a) == absl::ascii_tolower(b);
}
void BM_Search(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize - 1,
kHaystack + kHaystackSize));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Search);
void BM_SearchMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize - 2,
kHaystack + kHaystackSize));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_SearchMedium);
void BM_SearchPathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize / 2,
kHaystack + kHaystackSize));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_SearchPathological);
void BM_Searchcase(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize - 1,
kHaystack + kHaystackSize, case_eq));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Searchcase);
void BM_SearchcaseMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize - 2,
kHaystack + kHaystackSize, case_eq));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_SearchcaseMedium);
void BM_SearchcasePathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
kHaystack + kHaystackSize / 2,
kHaystack + kHaystackSize, case_eq));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_SearchcasePathological);
char* memcasechr(const char* s, int c, size_t slen) {
c = absl::ascii_tolower(c);
for (; slen; ++s, --slen) {
if (absl::ascii_tolower(*s) == c) return const_cast<char*>(s);
}
return nullptr;
}
const char* memcasematch(const char* phaystack, size_t haylen,
const char* pneedle, size_t neelen) {
if (0 == neelen) {
return phaystack; // even if haylen is 0
}
if (haylen < neelen) return nullptr;
const char* match;
const char* hayend = phaystack + haylen - neelen + 1;
while ((match = static_cast<char*>(
memcasechr(phaystack, pneedle[0], hayend - phaystack)))) {
if (absl::strings_internal::memcasecmp(match, pneedle, neelen) == 0)
return match;
else
phaystack = match + 1;
}
return nullptr;
}
void BM_Memmatch(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memmatch(kHaystack, kHaystackSize, "b", 1));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Memmatch);
void BM_MemmatchMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
absl::strings_internal::memmatch(kHaystack, kHaystackSize, "ab", 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemmatchMedium);
void BM_MemmatchPathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(absl::strings_internal::memmatch(
kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
kHaystackSize - kHaystackSize / 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemmatchPathological);
void BM_Memcasematch(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize, "b", 1));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_Memcasematch);
void BM_MemcasematchMedium(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize, "ab", 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemcasematchMedium);
void BM_MemcasematchPathological(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize,
kHaystack + kHaystackSize / 2,
kHaystackSize - kHaystackSize / 2));
}
state.SetBytesProcessed(kHaystackSize64 * state.iterations());
}
BENCHMARK(BM_MemcasematchPathological);
void BM_MemmemStartup(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(absl::strings_internal::memmem(
kHaystack + kHaystackSize - 10, 10, kHaystack + kHaystackSize - 1, 1));
}
}
BENCHMARK(BM_MemmemStartup);
void BM_SearchStartup(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(
std::search(kHaystack + kHaystackSize - 10, kHaystack + kHaystackSize,
kHaystack + kHaystackSize - 1, kHaystack + kHaystackSize));
}
}
BENCHMARK(BM_SearchStartup);
void BM_MemmatchStartup(benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(absl::strings_internal::memmatch(
kHaystack + kHaystackSize - 10, 10, kHaystack + kHaystackSize - 1, 1));
}
}
BENCHMARK(BM_MemmatchStartup);
} // namespace
