usr/src/lib/libc/amd64/gen/memchr.s

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25
  26         .file   "memchr.s"
  27
  28 /
  29 / memchr(sptr, c1, n)
  30 /
  31 / Returns the pointer in sptr at which the character c1 appears;
  32 / or NULL if not found in chars; doesn't stop at \0.
  33 /
  34 / Fast assembly language version of the following C-program memchr
  35 / which represents the `standard' for the C-library.
  36 /
  37 /       void *
  38 /       memchr(const void *sptr, int c1, size_t n)
  39 /       {
  40 /               if (n != 0) {
  41 /                       unsigned char   c = (unsigned char)c1;
  42 /                       const unsigned char     *sp = sptr;
  43 /
  44 /                       do {
  45 /                               if (*sp++ == c)
  46 /                                       return ((void *)--sp);
  47 /                       } while (--n != 0);
  48 /               }
  49 /               return (NULL);
  50 /       }
  51 /
  52
  53 #include "SYS.h"
  54
  55         .globl  memchr
  56         .align  4
  57
  58         ENTRY(memchr) /* (void *s, uchar_t c, size_t n) */
  59         movl    %esi, %eax      / move "c" to %eax
  60         cmpq    $4, %rdx        / if number of bytes < 4
  61         jb      .L1             / goto .L1
  62         testq   $3, %rdi        / if %rdi not word aligned
  63         jnz     .L2             / goto .L2
  64         .align  4
  65 .L3:
  66         movl    (%rdi), %ecx    / move 1 word from (%rdi) to %ecx
  67         cmpb    %cl, %al        / if the first byte is %al
  68         je      .L4             / goto .L4 (found)
  69         cmpb    %ch, %al        / if the second byte is %al
  70         je      .L5             / goto .L5 (found)
  71         shrl    $16, %ecx       / right shift 16-bit
  72         cmpb    %cl, %al        / if the third byte is %al
  73         je      .L6             / goto .L6 (found)
  74         cmpb    %ch, %al        / if the fourth is %al
  75         je      .L7             / goto .L7 (found)
  76         subq    $4, %rdx        / decrement number of bytes by 4
  77         addq    $4, %rdi        / next word
  78         cmpq    $4, %rdx        / if number of bytes >= 4
  79         jae     .L3             / goto .L3
  80 .L1:
  81         cmpq    $0, %rdx        / if number of bytes == 0
  82         jz      .L8             / goto .L8 (not found)
  83         cmpb    (%rdi), %al     / if a byte in (%rdi) is %al
  84         je      .L4             / goto .L4 (found)
  85         decq    %rdx            / decrement number of bytes by 1
  86         incq    %rdi            / next byte
  87         jmp     .L1             / goto .L1
  88         .align  4
  89 .L8:
  90         xorl    %eax, %eax      / not found
  91         ret                     / return (0)
  92         .align  4
  93 .L2:
  94         cmpq    $0, %rdx        / if number of bytes == 0
  95         jz      .L8             / goto .L8 (not found)
  96         cmpb    (%rdi), %al     / if a byte in (%rdi) is %al
  97         je      .L4             / goto .L4 (found)
  98         incq    %rdi            / next byte
  99         decq    %rdx            / decrement number of bytes by 1
 100         testq   $3, %rdi        / if %rdi not word aligned
 101         jnz     .L2             / goto .L2
 102         cmpq    $4, %rdx        / if number of bytes >= 4
 103         jae     .L3             / goto .L3 (word aligned)
 104         jmp     .L1             / goto .L1
 105         .align  4
 106 .L7:
 107         / found at the fourth byte
 108         incq    %rdi
 109 .L6:
 110         / found at the third byte
 111         incq    %rdi
 112 .L5:
 113         / found at the second byte
 114         incq    %rdi
 115 .L4:
 116         / found at the first byte
 117         movq    %rdi,%rax
 118         ret
 119         SET_SIZE(memchr)