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/*
* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef VPX_VPX_PORTS_BITOPS_H_
#define VPX_VPX_PORTS_BITOPS_H_
#include <assert.h>
#include "vpx_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_lsb() and 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_lsb(unsigned int n) {
assert(n != 0);
return __builtin_ctz(n);
}
static INLINE int get_msb(unsigned int n) {
assert(n != 0);
return 31 ^ __builtin_clz(n);
}
#elif defined(USE_MSC_INTRINSICS)
#pragma intrinsic(_BitScanForward)
#pragma intrinsic(_BitScanReverse)
static INLINE int get_lsb(unsigned int n) {
unsigned long first_set_bit; // NOLINT(runtime/int)
_BitScanForward(&first_set_bit, n);
return first_set_bit;
}
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
static INLINE int get_lsb(unsigned int n) {
int i;
assert(n != 0);
for (i = 0; i < 32 && !(n & 1); ++i) n >>= 1;
return i;
}
// 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 // VPX_VPX_PORTS_BITOPS_H_
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