NetBSD/lib/libc/arch/i386/string/swab.S

71 lines
1.1 KiB
ArmAsm

/*
* Written by J.T. Conklin <jtc@netbsd.org>.
* Public domain.
*/
#include <machine/asm.h>
#if defined(LIBC_SCCS)
RCSID("$NetBSD: swab.S,v 1.9 1995/04/28 22:58:16 jtc Exp $")
#endif
/*
* On the i486, this code is negligibly faster than the code generated
* by gcc at about half the size. If my i386 databook is correct, it
* should be considerably faster than the gcc code on a i386.
*/
ENTRY(swab)
pushl %esi
pushl %edi
movl 12(%esp),%esi
movl 16(%esp),%edi
movl 20(%esp),%ecx
cld # set direction forward
shrl $1,%ecx
testl $7,%ecx # copy first group of 1 to 7 words
jz L2 # while swaping alternate bytes.
.align 2,0x90
L1: lodsw
rorw $8,%ax
stosw
decl %ecx
testl $7,%ecx
jnz L1
L2: shrl $3,%ecx # copy remainder 8 words at a time
jz L4 # while swapping alternate bytes.
.align 2,0x90
L3: lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
lodsw
rorw $8,%ax
stosw
decl %ecx
jnz L3
L4: popl %edi
popl %esi
ret