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129 lines
6.1 KiB
C++
129 lines
6.1 KiB
C++
/********************************************************************
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* *
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* THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE. *
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* USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
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* GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
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* IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
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* *
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* THE Theora SOURCE CODE IS COPYRIGHT (C) 2002-2009 *
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* by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
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* *
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********************************************************************
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function:
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last mod: $Id: ocintrin.h 16503 2009-08-22 18:14:02Z giles $
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********************************************************************/
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/*Some common macros for potential platform-specific optimization.*/
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#include <math.h>
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#if !defined(_ocintrin_H)
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# define _ocintrin_H (1)
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/*Some specific platforms may have optimized intrinsic or inline assembly
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versions of these functions which can substantially improve performance.
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We define macros for them to allow easy incorporation of these non-ANSI
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features.*/
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/*Note that we do not provide a macro for abs(), because it is provided as a
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library function, which we assume is translated into an intrinsic to avoid
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the function call overhead and then implemented in the smartest way for the
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target platform.
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With modern gcc (4.x), this is true: it uses cmov instructions if the
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architecture supports it and branchless bit-twiddling if it does not (the
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speed difference between the two approaches is not measurable).
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Interestingly, the bit-twiddling method was patented in 2000 (US 6,073,150)
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by Sun Microsystems, despite prior art dating back to at least 1996:
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http://web.archive.org/web/19961201174141/www.x86.org/ftp/articles/pentopt/PENTOPT.TXT
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On gcc 3.x, however, our assumption is not true, as abs() is translated to a
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conditional jump, which is horrible on deeply piplined architectures (e.g.,
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all consumer architectures for the past decade or more).
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Also be warned that -C*abs(x) where C is a constant is mis-optimized as
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abs(C*x) on every gcc release before 4.2.3.
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See bug http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34130 */
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/*Modern gcc (4.x) can compile the naive versions of min and max with cmov if
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given an appropriate architecture, but the branchless bit-twiddling versions
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are just as fast, and do not require any special target architecture.
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Earlier gcc versions (3.x) compiled both code to the same assembly
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instructions, because of the way they represented ((_b)>(_a)) internally.*/
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#define OC_MAXI(_a,_b) ((_a)-((_a)-(_b)&-((_b)>(_a))))
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#define OC_MINI(_a,_b) ((_a)+((_b)-(_a)&-((_b)<(_a))))
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/*Clamps an integer into the given range.
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If _a>_c, then the lower bound _a is respected over the upper bound _c (this
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behavior is required to meet our documented API behavior).
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_a: The lower bound.
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_b: The value to clamp.
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_c: The upper boud.*/
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#define OC_CLAMPI(_a,_b,_c) (OC_MAXI(_a,OC_MINI(_b,_c)))
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#define OC_CLAMP255(_x) ((unsigned char)((((_x)<0)-1)&((_x)|-((_x)>255))))
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/*This has a chance of compiling branchless, and is just as fast as the
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bit-twiddling method, which is slightly less portable, since it relies on a
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sign-extended rightshift, which is not guaranteed by ANSI (but present on
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every relevant platform).*/
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#define OC_SIGNI(_a) (((_a)>0)-((_a)<0))
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/*Slightly more portable than relying on a sign-extended right-shift (which is
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not guaranteed by ANSI), and just as fast, since gcc (3.x and 4.x both)
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compile it into the right-shift anyway.*/
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#define OC_SIGNMASK(_a) (-((_a)<0))
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/*Divides an integer by a power of two, truncating towards 0.
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_dividend: The integer to divide.
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_shift: The non-negative power of two to divide by.
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_rmask: (1<<_shift)-1*/
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#define OC_DIV_POW2(_dividend,_shift,_rmask)\
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((_dividend)+(OC_SIGNMASK(_dividend)&(_rmask))>>(_shift))
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/*Divides _x by 65536, truncating towards 0.*/
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#define OC_DIV2_16(_x) OC_DIV_POW2(_x,16,0xFFFF)
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/*Divides _x by 2, truncating towards 0.*/
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#define OC_DIV2(_x) OC_DIV_POW2(_x,1,0x1)
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/*Divides _x by 8, truncating towards 0.*/
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#define OC_DIV8(_x) OC_DIV_POW2(_x,3,0x7)
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/*Divides _x by 16, truncating towards 0.*/
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#define OC_DIV16(_x) OC_DIV_POW2(_x,4,0xF)
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/*Right shifts _dividend by _shift, adding _rval, and subtracting one for
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negative dividends first.
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When _rval is (1<<_shift-1), this is equivalent to division with rounding
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ties away from zero.*/
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#define OC_DIV_ROUND_POW2(_dividend,_shift,_rval)\
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((_dividend)+OC_SIGNMASK(_dividend)+(_rval)>>(_shift))
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/*Divides a _x by 2, rounding towards even numbers.*/
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#define OC_DIV2_RE(_x) ((_x)+((_x)>>1&1)>>1)
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/*Divides a _x by (1<<(_shift)), rounding towards even numbers.*/
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#define OC_DIV_POW2_RE(_x,_shift) \
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((_x)+((_x)>>(_shift)&1)+((1<<(_shift))-1>>1)>>(_shift))
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/*Swaps two integers _a and _b if _a>_b.*/
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#define OC_SORT2I(_a,_b) \
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do{ \
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int t__; \
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t__=((_a)^(_b))&-((_b)<(_a)); \
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(_a)^=t__; \
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(_b)^=t__; \
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} \
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while(0)
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/*Accesses one of four (signed) bytes given an index.
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This can be used to avoid small lookup tables.*/
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#define OC_BYTE_TABLE32(_a,_b,_c,_d,_i) \
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((signed char) \
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(((_a)&0xFF|((_b)&0xFF)<<8|((_c)&0xFF)<<16|((_d)&0xFF)<<24)>>(_i)*8))
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/*Accesses one of eight (unsigned) nibbles given an index.
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This can be used to avoid small lookup tables.*/
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#define OC_UNIBBLE_TABLE32(_a,_b,_c,_d,_e,_f,_g,_h,_i) \
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((((_a)&0xF|((_b)&0xF)<<4|((_c)&0xF)<<8|((_d)&0xF)<<12| \
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((_e)&0xF)<<16|((_f)&0xF)<<20|((_g)&0xF)<<24|((_h)&0xF)<<28)>>(_i)*4)&0xF)
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/*All of these macros should expect floats as arguments.*/
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#define OC_MAXF(_a,_b) ((_a)<(_b)?(_b):(_a))
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#define OC_MINF(_a,_b) ((_a)>(_b)?(_b):(_a))
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#define OC_CLAMPF(_a,_b,_c) (OC_MINF(_a,OC_MAXF(_b,_c)))
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#define OC_FABSF(_f) ((float)fabs(_f))
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#define OC_SQRTF(_f) ((float)sqrt(_f))
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#define OC_POWF(_b,_e) ((float)pow(_b,_e))
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#define OC_LOGF(_f) ((float)log(_f))
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#define OC_IFLOORF(_f) ((int)floor(_f))
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#define OC_ICEILF(_f) ((int)ceil(_f))
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#endif
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