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Diffstat (limited to 'vpx_ports/bitops.h')
-rw-r--r-- | vpx_ports/bitops.h | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/vpx_ports/bitops.h b/vpx_ports/bitops.h new file mode 100644 index 000000000..0d3223e32 --- /dev/null +++ b/vpx_ports/bitops.h @@ -0,0 +1,66 @@ +/* + * 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 "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 + +// use GNU builtins where available. +#if defined(__GNUC__) && \ + ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) +static INLINE int get_msb(unsigned int n) { + 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; + _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; + + 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_ |