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bits.h
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bits.h
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// Copyright Google Inc. All Rights Reserved.
//
// 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.
//
#ifndef S2_UTIL_BITS_BITS_H_
#define S2_UTIL_BITS_BITS_H_
#include <cstdint>
#include "absl/base/optimization.h"
#include "absl/numeric/bits.h"
// Use namespace because this used to be a static class.
namespace Bits {
inline int FindLSBSetNonZero(uint32_t n) {
// TODO: Investigate whether ABSL_ASSUME is needed at all, or if clang
// and gcc can prove the argument is non-zero where these are used.
ABSL_ASSUME(n != 0);
return absl::countr_zero(n);
}
inline int FindLSBSetNonZero64(uint64_t n) {
ABSL_ASSUME(n != 0);
return absl::countr_zero(n);
}
inline int Log2FloorNonZero(uint32_t n) {
ABSL_ASSUME(n != 0);
return absl::bit_width(n) - 1;
}
inline int Log2FloorNonZero64(uint64_t n) {
ABSL_ASSUME(n != 0);
return absl::bit_width(n) - 1;
}
inline int FindMSBSetNonZero(uint32_t n) { return Log2FloorNonZero(n); }
inline int FindMSBSetNonZero64(uint64_t n) { return Log2FloorNonZero64(n); }
inline int Log2Ceiling(uint32_t n) {
int floor = absl::bit_width(n) - 1;
if ((n & (n - 1)) == 0) { // zero or a power of two
return floor;
} else {
return floor + 1;
}
}
} // namespace Bits
#endif // S2_UTIL_BITS_BITS_H_