From 6c8338c252116e429307361ff4fdc1fd0532902d Mon Sep 17 00:00:00 2001 From: Ilya Tokar Date: Mon, 30 Oct 2023 12:20:56 -0700 Subject: [PATCH] Optimize memcasecmp. Benchmarks shows slight improvement. We are also avoiding potential cache-misses, by avoiding load. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit name old speed new speed delta BM_Searchcase 3.09GB/s ±13% 3.20GB/s ±16% +3.69% (p=0.039 n=20+17) BM_SearchcaseMedium 1.08GB/s ± 7% 1.04GB/s ±14% ~ (p=0.814 n=16+20) BM_SearchcasePathological 618kB/s ±13% 652kB/s ± 6% +5.55% (p=0.043 n=20+16) BM_Memcasematch 2.43GB/s ± 3% 2.45GB/s ± 3% ~ (p=0.488 n=17+16) BM_MemcasematchMedium 230MB/s ± 8% 261MB/s ±14% +13.77% (p=0.000 n=16+20) BM_MemcasematchPathological 624kB/s ±14% 619kB/s ±14% ~ (p=0.836 n=20+20) PiperOrigin-RevId: 577919033 Change-Id: I31324e04b6a577c582ad630d171d3b41d826f1e4 --- absl/strings/internal/memutil.cc | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/absl/strings/internal/memutil.cc b/absl/strings/internal/memutil.cc index e2e7347c49b..0bbd8aa1bd1 100644 --- a/absl/strings/internal/memutil.cc +++ b/absl/strings/internal/memutil.cc @@ -27,10 +27,18 @@ int memcasecmp(const char* s1, const char* s2, size_t len) { const unsigned char* us2 = reinterpret_cast(s2); for (size_t i = 0; i < len; i++) { - const int diff = - int{static_cast(absl::ascii_tolower(us1[i]))} - - int{static_cast(absl::ascii_tolower(us2[i]))}; - if (diff != 0) return diff; + unsigned char c1 = us1[i]; + unsigned char c2 = us2[i]; + // If bytes are the same, they will be the same when converted to lower. + // So we only need to convert if bytes are not equal. + // NOTE(b/308193381): We do not use `absl::ascii_tolower` here in order + // to avoid its lookup table and improve performance. + if (c1 != c2) { + c1 = c1 >= 'A' && c1 <= 'Z' ? c1 - 'A' + 'a' : c1; + c2 = c2 >= 'A' && c2 <= 'Z' ? c2 - 'A' + 'a' : c2; + const int diff = int{c1} - int{c2}; + if (diff != 0) return diff; + } } return 0; }