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.*/
#ifdef __GNUC_PREREQ
#if __GNUC_PREREQ(3,4)
# if INT_MAX>=2147483647
#  define EC_CLZ0 sizeof(unsigned)*CHAR_BIT
#  define EC_CLZ(_x) (__builtin_clz(_x))
# elif LONG_MAX>=2147483647L
#  define EC_CLZ0 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))
#elif defined(ENABLE_TI_DSPLIB)
#include "dsplib.h"
#define EC_ILOG(x) (31 - _lnorm(x))
#else
# define EC_ILOG(_x) (ec_ilog(_x))
#endif

#ifdef __GNUC_PREREQ
#if __GNUC_PREREQ(3,4)
# if INT_MAX>=9223372036854775807
#  define EC_CLZ64_0 sizeof(unsigned)*CHAR_BIT
#  define EC_CLZ64(_x) (__builtin_clz(_x))
# elif LONG_MAX>=9223372036854775807L
#  define EC_CLZ64_0 sizeof(unsigned long)*CHAR_BIT
#  define EC_CLZ64(_x) (__builtin_clzl(_x))
# elif LLONG_MAX>=9223372036854775807LL
#  define EC_CLZ64_0 sizeof(unsigned long long)*CHAR_BIT
#  define EC_CLZ64(_x) (__builtin_clzll(_x))
# endif
#endif
#endif

#if defined(EC_CLZ64)
/*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_ILOG64(_x) (EC_CLZ64_0-EC_CLZ64(_x))
#else
# define EC_ILOG64(_x) (ec_ilog64(_x))
#endif

#endif