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// bits.h
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#if defined(_MSC_VER)
#include <intrin.h>
#endif
namespace mongo {
/**
* Returns the number of leading 0-bits in num. Returns 64 if num is 0.
*/
inline int countLeadingZeros64(unsigned long long num);
/**
* Returns the number of trailing 0-bits in num. Returns 64 if num is 0.
*/
inline int countTrailingZeros64(unsigned long long num);
#if defined(__GNUC__)
int countLeadingZeros64(unsigned long long num) {
if (num == 0)
return 64;
return __builtin_clzll(num);
}
int countTrailingZeros64(unsigned long long num) {
if (num == 0)
return 64;
return __builtin_ctzll(num);
}
#elif defined(_MSC_VER) && defined(_WIN64)
int countLeadingZeros64(unsigned long long num) {
unsigned long out;
if (_BitScanReverse64(&out, num))
return 63 ^ out;
return 64;
}
int countTrailingZeros64(unsigned long long num) {
unsigned long out;
if (_BitScanForward64(&out, num))
return out;
return 64;
}
#elif defined(_MSC_VER) && defined(_WIN32)
int countLeadingZeros64(unsigned long long num) {
unsigned long out;
if (_BitScanReverse(&out, static_cast<unsigned long>(num >> 32)))
return 31 ^ out;
if (_BitScanReverse(&out, static_cast<unsigned long>(num)))
return 63 ^ out;
return 64;
}
int countTrailingZeros64(unsigned long long num) {
unsigned long out;
if (_BitScanForward(&out, static_cast<unsigned long>(num)))
return out;
if (_BitScanForward(&out, static_cast<unsigned long>(num >> 32)))
return out + 32;
return 64;
}
#else
#error "No bit-ops definitions for your platform"
#endif
}
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