re2/bitmap256.cc

// Copyright 2023 The RE2 Authors.  All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "re2/bitmap256.h"

#include <stdint.h>

#include "absl/log/absl_check.h"

namespace re2 {

int Bitmap256::FindNextSetBit(int c) const {
  ABSL_DCHECK_GE(c, 0);
  ABSL_DCHECK_LE(c, 255);

  // Check the word that contains the bit. Mask out any lower bits.
  int i = c / 64;
  uint64_t word = words_[i] & (~uint64_t{0} << (c % 64));
  if (word != 0)
    return (i * 64) + FindLSBSet(word);

  // Check any following words.
  i++;
  switch (i) {
    case 1:
      if (words_[1] != 0)
        return (1 * 64) + FindLSBSet(words_[1]);
      [[fallthrough]];
    case 2:
      if (words_[2] != 0)
        return (2 * 64) + FindLSBSet(words_[2]);
      [[fallthrough]];
    case 3:
      if (words_[3] != 0)
        return (3 * 64) + FindLSBSet(words_[3]);
      [[fallthrough]];
    default:
      return -1;
  }
}

}  // namespace re2