ports/sysdeps/m68k/strchrnul.S

   1 /* strchrnul (str, ch) -- Return pointer to first occurrence of CH in STR
   2    or the final NUL byte.
   3    For Motorola 68000.
   4    Copyright (C) 1999-2014 Free Software Foundation, Inc.
   5    This file is part of the GNU C Library.
   6    Contributed by Andreas Schwab <schwab@gnu.org>.
   7
   8    The GNU C Library is free software; you can redistribute it and/or
   9    modify it under the terms of the GNU Lesser General Public
  10    License as published by the Free Software Foundation; either
  11    version 2.1 of the License, or (at your option) any later version.
  12
  13    The GNU C Library is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16    Lesser General Public License for more details.
  17
  18    You should have received a copy of the GNU Lesser General Public
  19    License along with the GNU C Library.  If not, see
  20    <http://www.gnu.org/licenses/>.  */
  21
  22 #include <sysdep.h>
  23 #include "asm-syntax.h"
  24
  25         TEXT
  26 ENTRY(__strchrnul)
  27         /* Save the callee-saved registers we use.  */
  28         movel   R(d2),MEM_PREDEC(sp)
  29         cfi_adjust_cfa_offset (4)
  30         movel   R(d3),MEM_PREDEC(sp)
  31         cfi_adjust_cfa_offset (4)
  32         cfi_rel_offset (R(d2), 4)
  33         cfi_rel_offset (R(d3), 0)
  34
  35         /* Get string pointer and character.  */
  36         movel   MEM_DISP(sp,12),R(a0)
  37         moveb   MEM_DISP(sp,19),R(d0)
  38
  39         /* Distribute the character to all bytes of a longword.  */
  40         movel   R(d0),R(d1)
  41         lsll    #8,R(d1)
  42         moveb   R(d0),R(d1)
  43         movel   R(d1),R(d0)
  44         swap    R(d0)
  45         movew   R(d1),R(d0)
  46
  47         /* First search for the character one byte at a time until the
  48            pointer is aligned to a longword boundary.  */
  49         movel   R(a0),R(d1)
  50 #ifdef __mcoldfire__
  51         andl    #3,R(d1)
  52 #else
  53         andw    #3,R(d1)
  54 #endif
  55         beq     L(L1)
  56         moveb   MEM(a0),R(d2)
  57         cmpb    R(d0),R(d2)
  58         beq     L(L9)
  59         tstb    R(d2)
  60         beq     L(L9)
  61         addql   #1,R(a0)
  62
  63 #ifdef __mcoldfire__
  64         subql   #3,R(d1)
  65 #else
  66         subqw   #3,R(d1)
  67 #endif
  68         beq     L(L1)
  69         moveb   MEM(a0),R(d2)
  70         cmpb    R(d0),R(d2)
  71         beq     L(L9)
  72         tstb    R(d2)
  73         beq     L(L9)
  74         addql   #1,R(a0)
  75
  76 #ifdef __mcoldfire__
  77         addql   #1,R(d1)
  78 #else
  79         addqw   #1,R(d1)
  80 #endif
  81         beq     L(L1)
  82         moveb   MEM(a0),R(d2)
  83         cmpb    R(d0),R(d2)
  84         beq     L(L9)
  85         tstb    R(d2)
  86         beq     L(L9)
  87         addql   #1,R(a0)
  88
  89 L(L1:)
  90         /* Load the magic bits.  Unlike the generic implementation we can
  91            use the carry bit as the fourth hole.  */
  92         movel   #0xfefefeff,R(d3)
  93
  94       /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
  95          change any of the hole bits of LONGWORD.
  96
  97          1) Is this safe?  Will it catch all the zero bytes?
  98          Suppose there is a byte with all zeros.  Any carry bits
  99          propagating from its left will fall into the hole at its
 100          least significant bit and stop.  Since there will be no
 101          carry from its most significant bit, the LSB of the
 102          byte to the left will be unchanged, and the zero will be
 103          detected.
 104
 105          2) Is this worthwhile?  Will it ignore everything except
 106          zero bytes?  Suppose every byte of LONGWORD has a bit set
 107          somewhere.  There will be a carry into bit 8.  If bit 8
 108          is set, this will carry into bit 16.  If bit 8 is clear,
 109          one of bits 9-15 must be set, so there will be a carry
 110          into bit 16.  Similarly, there will be a carry into bit
 111          24.  If one of bits 24-31 is set, there will be a carry
 112          into bit 32 (=carry flag), so all of the hole bits will
 113          be changed.
 114
 115          3) But wait!  Aren't we looking for C, not zero?
 116          Good point.  So what we do is XOR LONGWORD with a longword,
 117          each of whose bytes is C.  This turns each byte that is C
 118          into a zero.  */
 119
 120 L(L2:)
 121         /* Get the longword in question.  */
 122         movel   MEM_POSTINC(a0),R(d1)
 123         /* XOR with the byte we search for.  */
 124         eorl    R(d0),R(d1)
 125
 126         /* Add the magic value.  We get carry bits reported for each byte
 127            which is not C.  */
 128         movel   R(d3),R(d2)
 129         addl    R(d1),R(d2)
 130
 131         /* Check the fourth carry bit before it is clobbered by the next
 132            XOR.  If it is not set we have a hit.  */
 133         bcc     L(L8)
 134
 135         /* We are only interested in carry bits that change due to the
 136            previous add, so remove original bits.  */
 137         eorl    R(d1),R(d2)
 138
 139         /* Now test for the other three overflow bits.
 140            Set all non-carry bits.  */
 141         orl     R(d3),R(d2)
 142         /* Add 1 to get zero if all carry bits were set.  */
 143         addql   #1,R(d2)
 144
 145         /* If we don't get zero then at least one byte of the word equals
 146            C.  */
 147         bne     L(L8)
 148
 149         /* Next look for a NUL byte.
 150            Restore original longword without reload.  */
 151         eorl    R(d0),R(d1)
 152         /* Add the magic value.  We get carry bits reported for each byte
 153            which is not NUL.  */
 154         movel   R(d3),R(d2)
 155         addl    R(d1),R(d2)
 156
 157         /* Check the fourth carry bit before it is clobbered by the next
 158            XOR.  If it is not set we have a hit.  */
 159         bcc     L(L8)
 160
 161         /* We are only interested in carry bits that change due to the
 162            previous add, so remove original bits.  */
 163         eorl    R(d1),R(d2)
 164
 165         /* Now test for the other three overflow bits.
 166            Set all non-carry bits.  */
 167         orl     R(d3),R(d2)
 168         /* Add 1 to get zero if all carry bits were set.  */
 169         addql   #1,R(d2)
 170
 171         /* If we don't get zero then at least one byte of the word was
 172            NUL.  Otherwise continue with the next longword.  */
 173         bne     L(L8)
 174
 175         /* Get the longword in question.  */
 176         movel   MEM_POSTINC(a0),R(d1)
 177         /* XOR with the byte we search for.  */
 178         eorl    R(d0),R(d1)
 179
 180         /* Add the magic value.  We get carry bits reported for each byte
 181            which is not C.  */
 182         movel   R(d3),R(d2)
 183         addl    R(d1),R(d2)
 184
 185         /* Check the fourth carry bit before it is clobbered by the next
 186            XOR.  If it is not set we have a hit.  */
 187         bcc     L(L8)
 188
 189         /* We are only interested in carry bits that change due to the
 190            previous add, so remove original bits */
 191         eorl    R(d1),R(d2)
 192
 193         /* Now test for the other three overflow bits.
 194            Set all non-carry bits.  */
 195         orl     R(d3),R(d2)
 196         /* Add 1 to get zero if all carry bits were set.  */
 197         addql   #1,R(d2)
 198
 199         /* If we don't get zero then at least one byte of the word equals
 200            C.  */
 201         bne     L(L8)
 202
 203         /* Next look for a NUL byte.
 204            Restore original longword without reload.  */
 205         eorl    R(d0),R(d1)
 206         /* Add the magic value.  We get carry bits reported for each byte
 207            which is not NUL.  */
 208         movel   R(d3),R(d2)
 209         addl    R(d1),R(d2)
 210
 211         /* Check the fourth carry bit before it is clobbered by the next
 212            XOR.  If it is not set we have a hit.  */
 213         bcc     L(L8)
 214
 215         /* We are only interested in carry bits that change due to the
 216            previous add, so remove original bits */
 217         eorl    R(d1),R(d2)
 218
 219         /* Now test for the other three overflow bits.
 220            Set all non-carry bits.  */
 221         orl     R(d3),R(d2)
 222         /* Add 1 to get zero if all carry bits were set.  */
 223         addql   #1,R(d2)
 224
 225         /* If we don't get zero then at least one byte of the word was
 226            NUL.  Otherwise continue with the next longword.  */
 227         beq     L(L2)
 228
 229 L(L8:)
 230         /* We have a hit.  Check to see which byte it was.  First
 231            compensate for the autoincrement in the loop.  */
 232         subql   #4,R(a0)
 233
 234         moveb   MEM(a0),R(d1)
 235         cmpb    R(d0),R(d1)
 236         beq     L(L9)
 237         tstb    R(d1)
 238         beq     L(L9)
 239         addql   #1,R(a0)
 240
 241         moveb   MEM(a0),R(d1)
 242         cmpb    R(d0),R(d1)
 243         beq     L(L9)
 244         tstb    R(d1)
 245         beq     L(L9)
 246         addql   #1,R(a0)
 247
 248         moveb   MEM(a0),R(d1)
 249         cmpb    R(d0),R(d1)
 250         beq     L(L9)
 251         tstb    R(d1)
 252         beq     L(L9)
 253         addql   #1,R(a0)
 254
 255         /* Otherwise the fourth byte must equal C or be NUL.  */
 256 L(L9:)
 257         movel   R(a0),R(d0)
 258         movel   MEM_POSTINC(sp),R(d3)
 259         cfi_adjust_cfa_offset (-4)
 260         cfi_restore (R(d3))
 261         movel   MEM_POSTINC(sp),R(d2)
 262         cfi_adjust_cfa_offset (-4)
 263         cfi_restore (R(d2))
 264         rts
 265 END(__strchrnul)
 266
 267 weak_alias (__strchrnul, strchrnul)