swab.S revision 1.10
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 1.10 1999/08/23 08:45:11 kleink 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 cld # set direction forward 26 27 shrl $1,%ecx 28 testl $7,%ecx # copy first group of 1 to 7 words 29 jz L2 # while swaping alternate bytes. 30 _ALIGN_TEXT,0x90 31 L1: lodsw 32 rorw $8,%ax 33 stosw 34 decl %ecx 35 testl $7,%ecx 36 jnz L1 37 38 L2: shrl $3,%ecx # copy remainder 8 words at a time 39 jz L4 # while swapping alternate bytes. 40 _ALIGN_TEXT,0x90 41 L3: 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 lodsw 63 rorw $8,%ax 64 stosw 65 decl %ecx 66 jnz L3 67 68 L4: popl %edi 69 popl %esi 70 ret 71
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