absl/strings/internal/memutil.cc

// Copyright 2017 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
//
//      https://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 <cstdlib>

#include "absl/strings/ascii.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace strings_internal {

int memcasecmp(const char* s1, const char* s2, size_t len) {
  const unsigned char* us1 = reinterpret_cast<const unsigned char*>(s1);
  const unsigned char* us2 = reinterpret_cast<const unsigned char*>(s2);

  for (size_t i = 0; i < len; i++) {
    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;
}

}  // namespace strings_internal
ABSL_NAMESPACE_END
}  // namespace absl