1 /* $OpenBSD: swab.S,v 1.3 2005/08/07 11:30:38 espie Exp $ */ 2 /* 3 * Written by J.T. Conklin <jtc (at) netbsd.org>. 4 * Public domain. 5 */ 6 7 #include <machine/asm.h> 8 9 /* 10 * On the i486, this code is negligibly faster than the code generated 11 * by gcc at about half the size. If my i386 databook is correct, it 12 * should be considerably faster than the gcc code on a i386. 13 */ 14 15 ENTRY(swab) 16 pushl %esi 17 pushl %edi 18 movl 12(%esp),%esi 19 movl 16(%esp),%edi 20 movl 20(%esp),%ecx 21 22 cld # set direction forward 23 24 shrl $1,%ecx 25 testl $7,%ecx # copy first group of 1 to 7 words 26 jz L2 # while swaping alternate bytes. 27 .align 2,0x90 28 L1: lodsw 29 rorw $8,%ax 30 stosw 31 decl %ecx 32 testl $7,%ecx 33 jnz L1 34 35 L2: shrl $3,%ecx # copy remainder 8 words at a time 36 jz L4 # while swapping alternate bytes. 37 .align 2,0x90 38 L3: lodsw 39 rorw $8,%ax 40 stosw 41 lodsw 42 rorw $8,%ax 43 stosw 44 lodsw 45 rorw $8,%ax 46 stosw 47 lodsw 48 rorw $8,%ax 49 stosw 50 lodsw 51 rorw $8,%ax 52 stosw 53 lodsw 54 rorw $8,%ax 55 stosw 56 lodsw 57 rorw $8,%ax 58 stosw 59 lodsw 60 rorw $8,%ax 61 stosw 62 decl %ecx 63 jnz L3 64 65 L4: popl %edi 66 popl %esi 67 ret 68
