ref: fb209003a8b9f1c52b2512391a74004b898e749c
dir: /vpx_ports/bitops.h/
/* * 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 # include <math.h> // the ceil() definition must precede intrin.h # if _MSC_VER > 1310 && (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_