[MPlayer-dev-eng] Re: ffmpeg byteswap

Bohdan Horst nexus at irc.pl
Thu Nov 14 18:06:38 CET 2002


On Thu, Nov 14, 2002 at 01:58:14PM -0200, Mario Sergio Fujikawa Ferreira wrote:
> On Thu, Nov 14, 2002 at 12:48:09PM +0100, Bohdan Horst wrote:
> > 
> > are there any performance differences between:
> > 
> > 
> > from original libavcodec/bswap.h:
> > 
> > inline static unsigned short ByteSwap16(unsigned short x)
> > {
> >   __asm("xchgb %b0,%h0" :
> >         "=q" (x)        :
> >         "0" (x));
> >     return x;
> > }
> > 
> > inline static unsigned int ByteSwap32(unsigned int x)
> > {
> > #if __CPU__ > 386
> >  __asm("bswap   %0":
> >       "=r" (x)     :
> > #else
> >  __asm("xchgb   %b0,%h0\n"
> >       " rorl    $16,%0\n"
> >       " xchgb   %b0,%h0":
> >       "=q" (x)          :
> > #endif
> >       "0" (x));
> >   return x;
> > }
> > 
> > 
> > and from FreeBSD-STABLE native:
> > 
> > sys/endian.h -> machine/endian.h ($FreeBSD: src/sys/i386/include/endian.h,v 1.18 1999/12/29 04:33:01 peter Exp $)
> > 
> > #define __byte_swap_word(x) \
> > __extension__ ({ register u_short __X = (x); \
> >    __asm ("xchgb %h1, %b1" \
> >         : "=q" (__X) \
> >         : "0" (__X)); \
> >    __X; })
> > 
> > 
> > #if defined(_KERNEL) && (defined(I486_CPU) || defined(I586_CPU) || defined(I686_CPU)) && !defined(I386_CPU)
> > #define __byte_swap_long(x) \
> > __extension__ ({ register u_long __X = (x); \
> >    __asm ("bswap %0" \
> >         : "=r" (__X) \
> >         : "0" (__X)); \
> >    __X; })
> > #else
> > #define __byte_swap_long(x) \
> > __extension__ ({ register u_long __X = (x); \
> >    __asm ("xchgb %h1, %b1\n\trorl $16, %1\n\txchgb %h1, %b1" \
> >         : "=q" (__X) \
> >         : "0" (__X)); \
> >    __X; })
> > #endif
> > 
> > 
> > in my tests both works very very similar (i made some benchmarks)
> 
> 	Actually, I am relying on "Steve O'Hara-Smith" <steve at sohara.org>
> and on freebsd-multimedia at FreeBSD.org for benchmark feedback.
> 	The optimized byteswap I'm using under FreeBSD is as follows
> 
> ENTRY(ntohl)
>         movl    4(%esp),%eax
>         xchgb   %al,%ah
>         roll    $16,%eax
>         xchgb   %al,%ah
>         ret
> 
> ENTRY(ntohs)
>         movzwl  4(%esp),%eax
>         xchgb   %al,%ah
>         ret
> 
> #define be16toh(x)      ntohs((x))
> #define be32toh(x)      ntohl((x))
> 
> #define bswap_16(x) (be16toh(x))
> #define bswap_32(x) (be32toh(x))
> 
> 	Could you try against these? At "close" inspection
> they're ridiculously similar to ffmpeg code. I apologize
> but my i386 asm is rusty, almost dead. :(
> 	My desire to prefer the FreeBSD code was two-fold
> 
> 	1) Hope that the FreeBSD code would get better
> with increased versions but ffmpeg can cope with that ease
> 
> 	2) Hope to be cross platform since the macro
> points to an adequate byteswap for that platform (x86, ia64, alpha
> ...)
> 
> 	Well, let me know what you're findings are.

can anyone take a short look at differences noticed above ?

my asm konwledge is about 0 :(

included:
freebsd ffmpeg byteswap patch: patch-libavcodec::bswap.h
freebsd include file: machine/endian.h

best regards

-- 
 /  irl: Bohdan 'Nexus' Horst  |  irc: Nexus  \
{----------------------v-------^---------------}
 \ http://irc.pl/nexus | mailto: nexus at irc.pl /
-------------- next part --------------
--- libavcodec/bswap.h.orig	Sun Nov  3 04:51:51 2002
+++ libavcodec/bswap.h	Sun Nov  3 04:53:30 2002
@@ -5,6 +5,14 @@
 #include <byteswap.h>
 #else
 
+#if (defined(__unix__) || defined(unix)) && !defined(USG)
+#include <sys/param.h>
+#endif
+
+#if defined(__FreeBSD__) && __FreeBSD_version >= 470000
+#include <sys/endian.h>
+#endif
+
 #ifdef ARCH_X86
 inline static unsigned short ByteSwap16(unsigned short x)
 {
@@ -13,7 +21,11 @@
         "0" (x));
     return x;
 }
+#if defined(__FreeBSD__) && __FreeBSD_version >= 470000
+#define bswap_16(x) (be16toh(x))
+#else
 #define bswap_16(x) ByteSwap16(x)
+#endif
 
 inline static unsigned int ByteSwap32(unsigned int x)
 {
@@ -29,7 +41,11 @@
       "0" (x));
   return x;
 }
+#if defined(__FreeBSD__) && __FreeBSD_version >= 470000
+#define bswap_32(x) (be32toh(x))
+#else
 #define bswap_32(x) ByteSwap32(x)
+#endif
 
 inline static unsigned long long int ByteSwap64(unsigned long long int x)
 {
-------------- next part --------------
/*
 * Copyright (c) 1987, 1991 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
 *
 *	from: @(#)endian.h	7.8 (Berkeley) 4/3/91
 * $FreeBSD: src/sys/i386/include/endian.h,v 1.18 1999/12/29 04:33:01 peter Exp $
 */

#ifndef _MACHINE_ENDIAN_H_
#define	_MACHINE_ENDIAN_H_

/*
 * Define the order of 32-bit words in 64-bit words.
 */
#define	_QUAD_HIGHWORD 1
#define	_QUAD_LOWWORD 0

#ifndef _POSIX_SOURCE

/*
 * Definitions for byte order, according to byte significance from low
 * address to high.
 */
#define	LITTLE_ENDIAN	1234	/* LSB first: i386, vax */
#define	BIG_ENDIAN	4321	/* MSB first: 68000, ibm, net */
#define	PDP_ENDIAN	3412	/* LSB first in word, MSW first in long */

#define	BYTE_ORDER	LITTLE_ENDIAN

#ifndef _KERNEL
#include <sys/cdefs.h>
#endif

__BEGIN_DECLS
unsigned long	htonl __P((unsigned long));
unsigned short	htons __P((unsigned short));
unsigned long	ntohl __P((unsigned long));
unsigned short	ntohs __P((unsigned short));
__END_DECLS

#define __word_swap_long(x) \
__extension__ ({ register u_long __X = (x); \
   __asm ("rorl $16, %1" \
	: "=r" (__X) \
	: "0" (__X)); \
   __X; })

#if defined(_KERNEL) && (defined(I486_CPU) || defined(I586_CPU) || defined(I686_CPU)) && !defined(I386_CPU)

#define __byte_swap_long(x) \
__extension__ ({ register u_long __X = (x); \
   __asm ("bswap %0" \
	: "=r" (__X) \
	: "0" (__X)); \
   __X; })
#else

#define __byte_swap_long(x) \
__extension__ ({ register u_long __X = (x); \
   __asm ("xchgb %h1, %b1\n\trorl $16, %1\n\txchgb %h1, %b1" \
	: "=q" (__X) \
	: "0" (__X)); \
   __X; })
#endif

#define __byte_swap_word(x) \
__extension__ ({ register u_short __X = (x); \
   __asm ("xchgb %h1, %b1" \
	: "=q" (__X) \
	: "0" (__X)); \
   __X; })

/*
 * Macros for network/external number representation conversion.
 */
#ifdef __GNUC__
#define	ntohl	__byte_swap_long
#define	ntohs	__byte_swap_word
#define	htonl	__byte_swap_long
#define	htons	__byte_swap_word
#endif

#define	NTOHL(x)	((x) = ntohl((u_long)(x)))
#define	NTOHS(x)	((x) = ntohs((u_short)(x)))
#define	HTONL(x)	((x) = htonl((u_long)(x)))
#define	HTONS(x)	((x) = htons((u_short)(x)))

#endif /* ! _POSIX_SOURCE */

#endif /* !_MACHINE_ENDIAN_H_ */


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