strchr.S revision 1.1
1 /* 2 * Written by J.T. Conklin <jtc (at) acorntoolworks.com> 3 * Public domain. 4 */ 5 6 #include <machine/asm.h> 7 8 #if defined(LIBC_SCCS) 9 RCSID("$NetBSD: strchr.S,v 1.1 2005/12/20 19:28:49 christos Exp $") 10 #endif 11 12 #ifdef INDEX 13 ENTRY(index) 14 #else 15 ENTRY(strchr) 16 #endif 17 pushl %esi 18 pushl %ebx 19 movl 12(%esp),%eax 20 movzbl 16(%esp),%ecx 21 22 /* 23 * Align to word boundary. 24 * Consider unrolling loop? 25 */ 26 .Lalign: 27 testb $3,%al 28 je .Lword_aligned 29 movb (%eax),%bl 30 cmpb %cl,%bl 31 je .Ldone 32 testb %bl,%bl 33 je .Lzero 34 incl %eax 35 jmp .Lalign 36 37 .Lword_aligned: 38 /* copy char to all bytes in word */ 39 movb %cl,%ch 40 movl %ecx,%edx 41 sall $16,%ecx 42 orl %edx,%ecx 43 44 /* Check whether any byte in the word is equal to ch or 0. */ 45 _ALIGN_TEXT 46 .Lloop: 47 movl (%eax),%ebx 48 addl $4,%eax 49 movl %ebx,%esi 50 leal -0x01010101(%ebx),%edx 51 xorl %ecx,%esi 52 subl $0x01010101,%esi 53 orl %esi,%edx 54 testl $0x80808080,%edx 55 je .Lloop 56 57 /* 58 * In rare cases, the above loop may exit prematurely. We must 59 * return to the loop if none of the bytes in the word match 60 * ch or are equal to 0. 61 */ 62 63 /* 64 * Alignment here avoids a stall on the Athlon, even though 65 * it's not a branch target. 66 */ 67 68 _ALIGN_TEXT 69 cmpb %cl,%bl /* 1st byte == ch? */ 70 jne 1f 71 subl $4,%eax 72 jmp .Ldone 73 1: testb %bl,%bl /* 1st byte == 0? */ 74 je .Lzero 75 76 cmpb %cl,%bh /* 2nd byte == ch? */ 77 jne 1f 78 subl $3,%eax 79 jmp .Ldone 80 1: testb %bh,%bh /* 2nd byte == 0? */ 81 je .Lzero 82 83 shrl $16,%ebx 84 cmpb %cl,%bl /* 3rd byte == ch? */ 85 jne 1f 86 subl $2,%eax 87 jmp .Ldone 88 1: testb %bl,%bl /* 3rd byte == 0? */ 89 je .Lzero 90 91 cmpb %cl,%bh /* 4th byte == ch? */ 92 jne 1f 93 decl %eax 94 jmp .Ldone 95 1: testb %bh,%bh /* 4th byte == 0? */ 96 jne .Lloop 97 98 .Lzero: 99 /* If a ch wasn't found, return 0. */ 100 xorl %eax,%eax 101 102 .Ldone: 103 popl %ebx 104 popl %esi 105 ret 106
Indexes created Thu Sep 25 16:09:42 GMT 2025