sysdeps/m68k/memchr.S

   1 /* memchr (str, ch, n) -- Return pointer to first occurrence of CH in the
   2    first N bytes of STR.
   3    For Motorola 68000.
   4    Copyright (C) 1999-2019 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(__memchr)
  27         /* Save the callee-saved registers we use.  */
  28 #ifdef __mcoldfire__
  29         movel   R(d2),MEM_PREDEC(sp)
  30         cfi_adjust_cfa_offset (4)
  31         movel   R(d3),MEM_PREDEC(sp)
  32         cfi_adjust_cfa_offset (4)
  33         movel   R(d4),MEM_PREDEC(sp)
  34         cfi_adjust_cfa_offset (4)
  35         cfi_rel_offset (R(d2), 8)
  36         cfi_rel_offset (R(d3), 4)
  37         cfi_rel_offset (R(d4), 0)
  38 #else
  39         moveml  R(d2)-R(d4),MEM_PREDEC(sp)
  40         cfi_adjust_cfa_offset (3*4)
  41         cfi_rel_offset (R(d2), 0)
  42         cfi_rel_offset (R(d3), 4)
  43         cfi_rel_offset (R(d4), 8)
  44 #endif
  45
  46         /* Get string pointer, character and length.  */
  47         movel   MEM_DISP(sp,16),R(a0)
  48         moveb   MEM_DISP(sp,23),R(d0)
  49         movel   MEM_DISP(sp,24),R(d4)
  50
  51         /* Check if at least four bytes left to search.  */
  52 #ifdef __mcoldfire__
  53         subql   #4,R(d4)
  54         bcs     L(L6)
  55         addql   #4,R(d4)
  56 #else
  57         moveql  #4,R(d1)
  58         cmpl    R(d1),R(d4)
  59         bcs     L(L6)
  60 #endif
  61
  62         /* Distribute the character to all bytes of a longword.  */
  63         movel   R(d0),R(d1)
  64         lsll    #8,R(d1)
  65         moveb   R(d0),R(d1)
  66         movel   R(d1),R(d0)
  67         swap    R(d0)
  68         movew   R(d1),R(d0)
  69
  70         /* First search for the character one byte at a time until the
  71            pointer is aligned to a longword boundary.  */
  72         movel   R(a0),R(d1)
  73 #ifdef __mcoldfire__
  74         andl    #3,R(d1)
  75 #else
  76         andw    #3,R(d1)
  77 #endif
  78         beq     L(L1)
  79         cmpb    MEM(a0),R(d0)
  80         beq     L(L9)
  81         addql   #1,R(a0)
  82         subql   #1,R(d4)
  83         beq     L(L7)
  84
  85 #ifdef __mcoldfire__
  86         subql   #3,R(d1)
  87 #else
  88         subqw   #3,R(d1)
  89 #endif
  90         beq     L(L1)
  91         cmpb    MEM(a0),R(d0)
  92         beq     L(L9)
  93         addql   #1,R(a0)
  94         subql   #1,R(d4)
  95         beq     L(L7)
  96
  97 #ifdef __mcoldfire__
  98         addql   #1,R(d1)
  99 #else
 100         addqw   #1,R(d1)
 101 #endif
 102         beq     L(L1)
 103         cmpb    MEM(a0),R(d0)
 104         beq     L(L9)
 105         addql   #1,R(a0)
 106         subql   #1,R(d4)
 107         beq     L(L7)
 108
 109 L(L1:)
 110         /* Load the magic bits.  Unlike the generic implementation we can
 111            use the carry bit as the fourth hole.  */
 112         movel   #0xfefefeff,R(d3)
 113
 114       /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
 115          change any of the hole bits of LONGWORD.
 116
 117          1) Is this safe?  Will it catch all the zero bytes?
 118          Suppose there is a byte with all zeros.  Any carry bits
 119          propagating from its left will fall into the hole at its
 120          least significant bit and stop.  Since there will be no
 121          carry from its most significant bit, the LSB of the
 122          byte to the left will be unchanged, and the zero will be
 123          detected.
 124
 125          2) Is this worthwhile?  Will it ignore everything except
 126          zero bytes?  Suppose every byte of LONGWORD has a bit set
 127          somewhere.  There will be a carry into bit 8.  If bit 8
 128          is set, this will carry into bit 16.  If bit 8 is clear,
 129          one of bits 9-15 must be set, so there will be a carry
 130          into bit 16.  Similarly, there will be a carry into bit
 131          24.  If one of bits 24-31 is set, there will be a carry
 132          into bit 32 (=carry flag), so all of the hole bits will
 133          be changed.
 134
 135          3) But wait!  Aren't we looking for C, not zero?
 136          Good point.  So what we do is XOR LONGWORD with a longword,
 137          each of whose bytes is C.  This turns each byte that is C
 138          into a zero.  */
 139
 140         /* Still at least 4 bytes to search?  */
 141         subql   #4,R(d4)
 142         bcs     L(L6)
 143
 144 L(L2:)
 145         /* Get the longword in question.  */
 146         movel   MEM_POSTINC(a0),R(d1)
 147         /* XOR with the byte we search for.  */
 148         eorl    R(d0),R(d1)
 149
 150         /* Add the magic value.  We get carry bits reported for each byte
 151            which is not C.  */
 152         movel   R(d3),R(d2)
 153         addl    R(d1),R(d2)
 154
 155         /* Check the fourth carry bit before it is clobbered by the next
 156            XOR.  If it is not set we have a hit.  */
 157         bcc     L(L8)
 158
 159         /* We are only interested in carry bits that change due to the
 160            previous add, so remove original bits.  */
 161         eorl    R(d1),R(d2)
 162
 163         /* Now test for the other three overflow bits.
 164            Set all non-carry bits.  */
 165         orl     R(d3),R(d2)
 166         /* Add 1 to get zero if all carry bits were set.  */
 167         addql   #1,R(d2)
 168
 169         /* If we don't get zero then at least one byte of the word equals
 170            C.  */
 171         bne     L(L8)
 172
 173         /* Still at least 4 bytes to search?  */
 174         subql   #4,R(d4)
 175         bcs     L(L6)
 176
 177         /* Get the longword in question.  */
 178         movel   MEM_POSTINC(a0),R(d1)
 179         /* XOR with the byte we search for.  */
 180         eorl    R(d0),R(d1)
 181
 182         /* Add the magic value.  We get carry bits reported for each byte
 183            which is not C.  */
 184         movel   R(d3),R(d2)
 185         addl    R(d1),R(d2)
 186
 187         /* Check the fourth carry bit before it is clobbered by the next
 188            XOR.  If it is not set we have a hit.  */
 189         bcc     L(L8)
 190
 191         /* We are only interested in carry bits that change due to the
 192            previous add, so remove original bits */
 193         eorl    R(d1),R(d2)
 194
 195         /* Now test for the other three overflow bits.
 196            Set all non-carry bits.  */
 197         orl     R(d3),R(d2)
 198         /* Add 1 to get zero if all carry bits were set.  */
 199         addql   #1,R(d2)
 200
 201         /* If we don't get zero then at least one byte of the word equals
 202            C.  */
 203         bne     L(L8)
 204
 205         /* Still at least 4 bytes to search?  */
 206         subql   #4,R(d4)
 207         bcc     L(L2)
 208
 209 L(L6:)
 210         /* Search one byte at a time in the remaining less than 4 bytes.  */
 211 #ifdef __mcoldfire__
 212         addql   #4,R(d4)
 213 #else
 214         andw    #3,R(d4)
 215 #endif
 216         beq     L(L7)
 217         cmpb    MEM(a0),R(d0)
 218         beq     L(L9)
 219         addql   #1,R(a0)
 220
 221 #ifdef __mcoldfire__
 222         subql   #1,R(d4)
 223 #else
 224         subqw   #1,R(d4)
 225 #endif
 226         beq     L(L7)
 227         cmpb    MEM(a0),R(d0)
 228         beq     L(L9)
 229         addql   #1,R(a0)
 230
 231 #ifdef __mcoldfire__
 232         subql   #1,R(d4)
 233 #else
 234         subqw   #1,R(d4)
 235 #endif
 236         beq     L(L7)
 237         cmpb    MEM(a0),R(d0)
 238         beq     L(L9)
 239
 240 L(L7:)
 241         /* Return NULL.  */
 242         clrl    R(d0)
 243         movel   R(d0),R(a0)
 244 #ifdef __mcoldfire__
 245         movel   MEM_POSTINC(sp),R(d4)
 246         cfi_remember_state
 247         cfi_adjust_cfa_offset (-4)
 248         cfi_restore (R(d4))
 249         movel   MEM_POSTINC(sp),R(d3)
 250         cfi_adjust_cfa_offset (-4)
 251         cfi_restore (R(d3))
 252         movel   MEM_POSTINC(sp),R(d2)
 253         cfi_adjust_cfa_offset (-4)
 254         cfi_restore (R(d2))
 255 #else
 256         moveml  MEM_POSTINC(sp),R(d2)-R(d4)
 257         cfi_remember_state
 258         cfi_adjust_cfa_offset (-3*4)
 259         cfi_restore (R(d2))
 260         cfi_restore (R(d3))
 261         cfi_restore (R(d4))
 262 #endif
 263         rts
 264
 265         cfi_restore_state
 266 L(L8:)
 267         /* We have a hit.  Check to see which byte it was.  First
 268            compensate for the autoincrement in the loop.  */
 269         subql   #4,R(a0)
 270
 271         cmpb    MEM(a0),R(d0)
 272         beq     L(L9)
 273         addql   #1,R(a0)
 274
 275         cmpb    MEM(a0),R(d0)
 276         beq     L(L9)
 277         addql   #1,R(a0)
 278
 279         cmpb    MEM(a0),R(d0)
 280         beq     L(L9)
 281         addql   #1,R(a0)
 282
 283         /* Otherwise the fourth byte must equal C.  */
 284 L(L9:)
 285         movel   R(a0),R(d0)
 286 #ifdef __mcoldfire__
 287         movel   MEM_POSTINC(sp),R(d4)
 288         cfi_adjust_cfa_offset (-4)
 289         cfi_restore (R(d4))
 290         movel   MEM_POSTINC(sp),R(d3)
 291         cfi_adjust_cfa_offset (-4)
 292         cfi_restore (R(d3))
 293         movel   MEM_POSTINC(sp),R(d2)
 294         cfi_adjust_cfa_offset (-4)
 295         cfi_restore (R(d2))
 296 #else
 297         moveml  MEM_POSTINC(sp),R(d2)-R(d4)
 298         cfi_adjust_cfa_offset (-3*4)
 299         cfi_restore (R(d2))
 300         cfi_restore (R(d3))
 301         cfi_restore (R(d4))
 302 #endif
 303         rts
 304 END(__memchr)
 305
 306 weak_alias (__memchr, memchr)
 307 libc_hidden_builtin_def (memchr)