76 lines
1.7 KiB
C
76 lines
1.7 KiB
C
/*
|
|
* 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_PORTS_BITOPS_H_
|
|
#define 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_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 // VPX_PORTS_BITOPS_H_
|