ref: 7bb26e13ca0523e195dc126547bfa8264008ff07
dir: /libcelt/ecintrin.h/
/* Copyright (c) 2003-2008 Timothy B. Terriberry
Copyright (c) 2008 Xiph.Org Foundation */
/*
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
- Neither the name of the Xiph.org Foundation nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*Some common macros for potential platform-specific optimization.*/
#include <math.h>
#include <limits.h>
#if !defined(_ecintrin_H)
# define _ecintrin_H (1)
/*Some specific platforms may have optimized intrinsic or inline assembly
versions of these functions which can substantially improve performance.
We define macros for them to allow easy incorporation of these non-ANSI
features.*/
/*Note that we do not provide a macro for abs(), because it is provided as a
library function, which we assume is translated into an intrinsic to avoid
the function call overhead and then implemented in the smartest way for the
target platform.
With modern gcc (4.x), this is true: it uses cmov instructions if the
architecture supports it and branchless bit-twiddling if it does not (the
speed difference between the two approaches is not measurable).
Interestingly, the bit-twiddling method was patented in 2000 (US 6,073,150)
by Sun Microsystems, despite prior art dating back to at least 1996:
http://web.archive.org/web/19961201174141/www.x86.org/ftp/articles/pentopt/PENTOPT.TXT
On gcc 3.x, however, our assumption is not true, as abs() is translated to a
conditional jump, which is horrible on deeply piplined architectures (e.g.,
all consumer architectures for the past decade or more) when the sign cannot
be reliably predicted.*/
/*Modern gcc (4.x) can compile the naive versions of min and max with cmov if
given an appropriate architecture, but the branchless bit-twiddling versions
are just as fast, and do not require any special target architecture.
Earlier gcc versions (3.x) compiled both code to the same assembly
instructions, because of the way they represented ((_b)>(_a)) internally.*/
#define EC_MAXI(_a,_b) ((_a)-((_a)-(_b)&-((_b)>(_a))))
#define EC_MINI(_a,_b) ((_a)+((_b)-(_a)&-((_b)<(_a))))
/*This has a chance of compiling branchless, and is just as fast as the
bit-twiddling method, which is slightly less portable, since it relies on a
sign-extended rightshift, which is not guaranteed by ANSI (but present on
every relevant platform).*/
#define EC_SIGNI(_a) (((_a)>0)-((_a)<0))
/*Slightly more portable than relying on a sign-extended right-shift (which is
not guaranteed by ANSI), and just as fast, since gcc (3.x and 4.x both)
compile it into the right-shift anyway.*/
#define EC_SIGNMASK(_a) (-((_a)<0))
/*Clamps an integer into the given range.
If _a>_c, then the lower bound _a is respected over the upper bound _c (this
behavior is required to meet our documented API behavior).
_a: The lower bound.
_b: The value to clamp.
_c: The upper boud.*/
#define EC_CLAMPI(_a,_b,_c) (EC_MAXI(_a,EC_MINI(_b,_c)))
/*Count leading zeros.
This macro should only be used for implementing ec_ilog(), if it is defined.
All other code should use EC_ILOG() instead.*/
#if defined(_MSC_VER)
# include <intrin.h>
static __inline int ec_bsr(unsigned long _x){
unsigned long ret;
_BitScanReverse(&ret,_x);
return (int)ret;
}
# define EC_CLZ0 (1)
# define EC_CLZ(_x) (-ec_bsr(_x))
#elif defined(ENABLE_TI_DSPLIB)
# include "dsplib.h"
# define EC_CLZ0 (31)
# define EC_CLZ(_x) (_lnorm(x))
#elif defined(__GNUC_PREREQ)
# if __GNUC_PREREQ(3,4)
# if INT_MAX>=2147483647
# define EC_CLZ0 ((int)sizeof(unsigned)*CHAR_BIT)
# define EC_CLZ(_x) (__builtin_clz(_x))
# elif LONG_MAX>=2147483647L
# define EC_CLZ0 ((int)sizeof(unsigned long)*CHAR_BIT)
# define EC_CLZ(_x) (__builtin_clzl(_x))
# endif
# endif
#endif
#if defined(EC_CLZ)
/*Note that __builtin_clz is not defined when _x==0, according to the gcc
documentation (and that of the BSR instruction that implements it on x86).
The majority of the time we can never pass it zero.
When we need to, it can be special cased.*/
# define EC_ILOG(_x) (EC_CLZ0-EC_CLZ(_x))
#else
# define EC_ILOG(_x) (ec_ilog(_x))
#endif
#endif