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/*
* Copyright (c) 2016, Alliance for Open Media. All rights reserved
*
* This source code is subject to the terms of the BSD 2 Clause License and
* the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
* was not distributed with this source code in the LICENSE file, you can
* obtain it at www.aomedia.org/license/software. If the Alliance for Open
* Media Patent License 1.0 was not distributed with this source code in the
* PATENTS file, you can obtain it at www.aomedia.org/license/patent.
*/
#ifndef AOM_PORTS_BITOPS_H_
#define AOM_PORTS_BITOPS_H_
#include <assert.h>
#include "aom_ports/msvc.h"
#ifdef _MSC_VER
#if defined(_M_X64) || defined(_M_IX86)
#include <intrin.h>
#define USE_MSC_INTRINSICS
#endif
#endif
#ifdef __cplusplus
extern "C" {
#endif
// These versions of get_msb() are only valid when n != 0 because all
// of the optimized versions are undefined when n == 0:
// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
// use GNU builtins where available.
#if defined(__GNUC__) && \
((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
static INLINE int get_msb(unsigned int n) {
assert(n != 0);
return 31 ^ __builtin_clz(n);
}
#elif defined(USE_MSC_INTRINSICS)
#pragma intrinsic(_BitScanReverse)
static INLINE int get_msb(unsigned int n) {
unsigned long first_set_bit;
assert(n != 0);
_BitScanReverse(&first_set_bit, n);
return first_set_bit;
}
#undef USE_MSC_INTRINSICS
#else
// Returns (int)floor(log2(n)). n must be > 0.
static INLINE int get_msb(unsigned int n) {
int log = 0;
unsigned int value = n;
int i;
assert(n != 0);
for (i = 4; i >= 0; --i) {
const int shift = (1 << i);
const unsigned int x = value >> shift;
if (x != 0) {
value = x;
log += shift;
}
}
return log;
}
#endif
#ifdef __cplusplus
} // extern "C"
#endif
#endif // AOM_PORTS_BITOPS_H_
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