124 lines
5.3 KiB
C
124 lines
5.3 KiB
C
/* Copyright (c) 2003-2008 Timothy B. Terriberry
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Copyright (c) 2008 Xiph.Org Foundation */
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/*
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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- Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*Some common macros for potential platform-specific optimization.*/
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#include "celt_types.h"
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#include <math.h>
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#include <limits.h>
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#if !defined(_ecintrin_H)
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# define _ecintrin_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) when the sign cannot
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be reliably predicted.*/
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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 EC_MAXI(_a,_b) ((_a)-((_a)-(_b)&-((_b)>(_a))))
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#define EC_MINI(_a,_b) ((_a)+((_b)-(_a)&-((_b)<(_a))))
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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 EC_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 EC_SIGNMASK(_a) (-((_a)<0))
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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 EC_CLAMPI(_a,_b,_c) (EC_MAXI(_a,EC_MINI(_b,_c)))
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/*Count leading zeros.
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This macro should only be used for implementing ec_ilog(), if it is defined.
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All other code should use EC_ILOG() instead.*/
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#if defined(_MSC_VER)
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# include <intrin.h>
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/*In _DEBUG mode this is not an intrinsic by default.*/
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# pragma intrinsic(_BitScanReverse)
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static __inline int ec_bsr(unsigned long _x){
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unsigned long ret;
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_BitScanReverse(&ret,_x);
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return (int)ret;
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}
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# define EC_CLZ0 (1)
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# define EC_CLZ(_x) (-ec_bsr(_x))
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#elif defined(ENABLE_TI_DSPLIB)
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# include "dsplib.h"
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# define EC_CLZ0 (31)
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# define EC_CLZ(_x) (_lnorm(_x))
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#elif defined(__GNUC_PREREQ)
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# if __GNUC_PREREQ(3,4)
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# if INT_MAX>=2147483647
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# define EC_CLZ0 ((int)sizeof(unsigned)*CHAR_BIT)
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# define EC_CLZ(_x) (__builtin_clz(_x))
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# elif LONG_MAX>=2147483647L
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# define EC_CLZ0 ((int)sizeof(unsigned long)*CHAR_BIT)
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# define EC_CLZ(_x) (__builtin_clzl(_x))
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# endif
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# endif
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#endif
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#if defined(EC_CLZ)
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/*Note that __builtin_clz is not defined when _x==0, according to the gcc
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documentation (and that of the BSR instruction that implements it on x86).
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The majority of the time we can never pass it zero.
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When we need to, it can be special cased.*/
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# define EC_ILOG(_x) (EC_CLZ0-EC_CLZ(_x))
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#else
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int ec_ilog(celt_uint32 _v);
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# define EC_ILOG(_x) (ec_ilog(_x))
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#endif
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#endif
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