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      1 /*
      2  * Written by J.T. Conklin <jtc (at) NetBSD.org>.
      3  * Public domain.
      4  */
      5 
      6 #include <machine/asm.h>
      7 
      8 #if defined(LIBC_SCCS)
      9 	RCSID("$NetBSD: swab.S,v 1.14 2014/05/23 02:34:19 uebayasi Exp $")
     10 #endif
     11 
     12 /*
     13  * On the i486, this code is negligibly faster than the code generated
     14  * by gcc at about half the size.  If my i386 databook is correct, it
     15  * should be considerably faster than the gcc code on a i386.
     16  */
     17 
     18 ENTRY(swab)
     19 	pushl	%esi
     20 	pushl	%edi
     21 	movl	12(%esp),%esi
     22 	movl	16(%esp),%edi
     23 	movl	20(%esp),%ecx
     24 
     25 	shrl	$1,%ecx
     26 	testl	$7,%ecx			# copy first group of 1 to 7 words
     27 	jz	L2			# while swapping alternate bytes.
     28 	_ALIGN_TEXT,0x90
     29 L1:	lodsw
     30 	rorw	$8,%ax
     31 	stosw
     32 	decl	%ecx
     33 	testl	$7,%ecx
     34 	jnz	L1
     35 
     36 L2:	shrl	$3,%ecx			# copy remainder 8 words at a time
     37 	jz	L4			# while swapping alternate bytes.
     38 	_ALIGN_TEXT,0x90
     39 L3:	lodsw
     40 	rorw	$8,%ax
     41 	stosw
     42 	lodsw
     43 	rorw	$8,%ax
     44 	stosw
     45 	lodsw
     46 	rorw	$8,%ax
     47 	stosw
     48 	lodsw
     49 	rorw	$8,%ax
     50 	stosw
     51 	lodsw
     52 	rorw	$8,%ax
     53 	stosw
     54 	lodsw
     55 	rorw	$8,%ax
     56 	stosw
     57 	lodsw
     58 	rorw	$8,%ax
     59 	stosw
     60 	lodsw
     61 	rorw	$8,%ax
     62 	stosw
     63 	decl	%ecx
     64 	jnz	L3
     65 
     66 L4:	popl	%edi
     67 	popl	%esi
     68 	ret
     69 END(swab)
     70