sysdeps/x86_64/strcspn.S

   1 /* strcspn (str, ss) -- Return the length of the initial segment of STR
   2                         which contains no characters from SS.
   3    For AMD x86-64.
   4    Copyright (C) 1994-2021 Free Software Foundation, Inc.
   5    This file is part of the GNU C Library.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <https://www.gnu.org/licenses/>.  */
  20
  21 #include <sysdep.h>
  22 #include "asm-syntax.h"
  23
  24         .text
  25 ENTRY (strcspn)
  26
  27         movq %rdi, %rdx         /* Save SRC.  */
  28
  29         /* First we create a table with flags for all possible characters.
  30            For the ASCII (7bit/8bit) or ISO-8859-X character sets which are
  31            supported by the C string functions we have 256 characters.
  32            Before inserting marks for the stop characters we clear the whole
  33            table.  */
  34         movq %rdi, %r8                  /* Save value.  */
  35         subq $256, %rsp                 /* Make space for 256 bytes.  */
  36         cfi_adjust_cfa_offset(256)
  37         movl $32,  %ecx                 /* 32*8 bytes = 256 bytes.  */
  38         movq %rsp, %rdi
  39         xorl %eax, %eax                 /* We store 0s.  */
  40         cld
  41         rep
  42         stosq
  43
  44         movq %rsi, %rax                 /* Setup skipset.  */
  45
  46 /* For understanding the following code remember that %rcx == 0 now.
  47    Although all the following instruction only modify %cl we always
  48    have a correct zero-extended 64-bit value in %rcx.  */
  49
  50         .p2align 4
  51 L(2):   movb (%rax), %cl        /* get byte from skipset */
  52         testb %cl, %cl          /* is NUL char? */
  53         jz L(1)                 /* yes => start compare loop */
  54         movb %cl, (%rsp,%rcx)   /* set corresponding byte in skipset table */
  55
  56         movb 1(%rax), %cl       /* get byte from skipset */
  57         testb $0xff, %cl        /* is NUL char? */
  58         jz L(1)                 /* yes => start compare loop */
  59         movb %cl, (%rsp,%rcx)   /* set corresponding byte in skipset table */
  60
  61         movb 2(%rax), %cl       /* get byte from skipset */
  62         testb $0xff, %cl        /* is NUL char? */
  63         jz L(1)                 /* yes => start compare loop */
  64         movb %cl, (%rsp,%rcx)   /* set corresponding byte in skipset table */
  65
  66         movb 3(%rax), %cl       /* get byte from skipset */
  67         addq $4, %rax           /* increment skipset pointer */
  68         movb %cl, (%rsp,%rcx)   /* set corresponding byte in skipset table */
  69         testb $0xff, %cl        /* is NUL char? */
  70         jnz L(2)                /* no => process next dword from skipset */
  71
  72 L(1):   leaq -4(%rdx), %rax     /* prepare loop */
  73
  74         /* We use a neat trick for the following loop.  Normally we would
  75            have to test for two termination conditions
  76            1. a character in the skipset was found
  77            and
  78            2. the end of the string was found
  79            But as a sign that the character is in the skipset we store its
  80            value in the table.  But the value of NUL is NUL so the loop
  81            terminates for NUL in every case.  */
  82
  83         .p2align 4
  84 L(3):   addq $4, %rax           /* adjust pointer for full loop round */
  85
  86         movb (%rax), %cl        /* get byte from string */
  87         cmpb %cl, (%rsp,%rcx)   /* is it contained in skipset? */
  88         je L(4)                 /* yes => return */
  89
  90         movb 1(%rax), %cl       /* get byte from string */
  91         cmpb %cl, (%rsp,%rcx)   /* is it contained in skipset? */
  92         je L(5)                 /* yes => return */
  93
  94         movb 2(%rax), %cl       /* get byte from string */
  95         cmpb %cl, (%rsp,%rcx)   /* is it contained in skipset? */
  96         jz L(6)                 /* yes => return */
  97
  98         movb 3(%rax), %cl       /* get byte from string */
  99         cmpb %cl, (%rsp,%rcx)   /* is it contained in skipset? */
 100         jne L(3)                /* no => start loop again */
 101
 102         incq %rax               /* adjust pointer */
 103 L(6):   incq %rax
 104 L(5):   incq %rax
 105
 106 L(4):   addq $256, %rsp         /* remove skipset */
 107         cfi_adjust_cfa_offset(-256)
 108 #ifdef USE_AS_STRPBRK
 109         xorl %edx,%edx
 110         orb %cl, %cl            /* was last character NUL? */
 111         cmovzq %rdx, %rax       /* Yes: return NULL */
 112 #else
 113         subq %rdx, %rax         /* we have to return the number of valid
 114                                    characters, so compute distance to first
 115                                    non-valid character */
 116 #endif
 117         ret
 118 END (strcspn)
 119 libc_hidden_builtin_def (strcspn)