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-/* strchr (str, ch) -- Return pointer to first occurrence of CH in STR.
- For Motorola 68000.
- Copyright (C) 1999, 2003 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Andreas Schwab <schwab@gnu.org>.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, write to the Free
- Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
- 02111-1307 USA. */
-
-#include <sysdep.h>
-#include "asm-syntax.h"
-
- TEXT
-ENTRY(strchr)
- /* Save the callee-saved registers we use. */
- movel R(d2),MEM_PREDEC(sp)
- movel R(d3),MEM_PREDEC(sp)
-
- /* Get string pointer and character. */
- movel MEM_DISP(sp,12),R(a0)
- moveb MEM_DISP(sp,19),R(d0)
-
- /* Distribute the character to all bytes of a longword. */
- movel R(d0),R(d1)
- lsll #8,R(d1)
- moveb R(d0),R(d1)
- movel R(d1),R(d0)
- swap R(d0)
- movew R(d1),R(d0)
-
- /* First search for the character one byte at a time until the
- pointer is aligned to a longword boundary. */
- movel R(a0),R(d1)
- andw #3,R(d1)
- beq L(L1)
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
- movel R(a0),R(d1)
- andw #3,R(d1)
- beq L(L1)
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
- movel R(a0),R(d1)
- andw #3,R(d1)
- beq L(L1)
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
-L(L1:)
- /* Load the magic bits. Unlike the generic implementation we can
- use the carry bit as the fourth hole. */
- movel #0xfefefeff,R(d3)
-
- /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
- change any of the hole bits of LONGWORD.
-
- 1) Is this safe? Will it catch all the zero bytes?
- Suppose there is a byte with all zeros. Any carry bits
- propagating from its left will fall into the hole at its
- least significant bit and stop. Since there will be no
- carry from its most significant bit, the LSB of the
- byte to the left will be unchanged, and the zero will be
- detected.
-
- 2) Is this worthwhile? Will it ignore everything except
- zero bytes? Suppose every byte of LONGWORD has a bit set
- somewhere. There will be a carry into bit 8. If bit 8
- is set, this will carry into bit 16. If bit 8 is clear,
- one of bits 9-15 must be set, so there will be a carry
- into bit 16. Similarly, there will be a carry into bit
- 24. If one of bits 24-31 is set, there will be a carry
- into bit 32 (=carry flag), so all of the hole bits will
- be changed.
-
- 3) But wait! Aren't we looking for C, not zero?
- Good point. So what we do is XOR LONGWORD with a longword,
- each of whose bytes is C. This turns each byte that is C
- into a zero. */
-
-L(L2:)
- /* Get the longword in question. */
- movel MEM_POSTINC(a0),R(d1)
- /* XOR with the byte we search for. */
- eorl R(d0),R(d1)
-
- /* Add the magic value. We get carry bits reported for each byte
- which is not C. */
- movel R(d3),R(d2)
- addl R(d1),R(d2)
-
- /* Check the fourth carry bit before it is clobbered by the next
- XOR. If it is not set we have a hit. */
- bcc L(L8)
-
- /* We are only interested in carry bits that change due to the
- previous add, so remove original bits. */
- eorl R(d1),R(d2)
-
- /* Now test for the other three overflow bits.
- Set all non-carry bits. */
- orl R(d3),R(d2)
- /* Add 1 to get zero if all carry bits were set. */
- addql #1,R(d2)
-
- /* If we don't get zero then at least one byte of the word equals
- C. */
- bne L(L8)
-
- /* Next look for a NUL byte.
- Restore original longword without reload. */
- eorl R(d0),R(d1)
- /* Add the magic value. We get carry bits reported for each byte
- which is not NUL. */
- movel R(d3),R(d2)
- addl R(d1),R(d2)
-
- /* Check the fourth carry bit before it is clobbered by the next
- XOR. If it is not set we have a hit, and return NULL. */
- bcc L(L3)
-
- /* We are only interested in carry bits that change due to the
- previous add, so remove original bits. */
- eorl R(d1),R(d2)
-
- /* Now test for the other three overflow bits.
- Set all non-carry bits. */
- orl R(d3),R(d2)
- /* Add 1 to get zero if all carry bits were set. */
- addql #1,R(d2)
-
- /* If we don't get zero then at least one byte of the word was NUL
- and we return NULL. Otherwise continue with the next longword. */
- bne L(L3)
-
- /* Get the longword in question. */
- movel MEM_POSTINC(a0),R(d1)
- /* XOR with the byte we search for. */
- eorl R(d0),R(d1)
-
- /* Add the magic value. We get carry bits reported for each byte
- which is not C. */
- movel R(d3),R(d2)
- addl R(d1),R(d2)
-
- /* Check the fourth carry bit before it is clobbered by the next
- XOR. If it is not set we have a hit. */
- bcc L(L8)
-
- /* We are only interested in carry bits that change due to the
- previous add, so remove original bits */
- eorl R(d1),R(d2)
-
- /* Now test for the other three overflow bits.
- Set all non-carry bits. */
- orl R(d3),R(d2)
- /* Add 1 to get zero if all carry bits were set. */
- addql #1,R(d2)
-
- /* If we don't get zero then at least one byte of the word equals
- C. */
- bne L(L8)
-
- /* Next look for a NUL byte.
- Restore original longword without reload. */
- eorl R(d0),R(d1)
- /* Add the magic value. We get carry bits reported for each byte
- which is not NUL. */
- movel R(d3),R(d2)
- addl R(d1),R(d2)
-
- /* Check the fourth carry bit before it is clobbered by the next
- XOR. If it is not set we have a hit, and return NULL. */
- bcc L(L3)
-
- /* We are only interested in carry bits that change due to the
- previous add, so remove original bits */
- eorl R(d1),R(d2)
-
- /* Now test for the other three overflow bits.
- Set all non-carry bits. */
- orl R(d3),R(d2)
- /* Add 1 to get zero if all carry bits were set. */
- addql #1,R(d2)
-
- /* If we don't get zero then at least one byte of the word was NUL
- and we return NULL. Otherwise continue with the next longword. */
- beq L(L2)
-
-L(L3:)
- /* Return NULL. */
- clrl R(d0)
- movel R(d0),R(a0)
- movel MEM_POSTINC(sp),R(d3)
- movel MEM_POSTINC(sp),R(d2)
- rts
-
-L(L8:)
- /* We have a hit. Check to see which byte it was. First
- compensate for the autoincrement in the loop. */
- subql #4,R(a0)
-
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
- moveb MEM(a0),R(d1)
- cmpb R(d0),R(d1)
- beq L(L9)
- tstb R(d1)
- beq L(L3)
- addql #1,R(a0)
-
- /* Otherwise the fourth byte must equal C. */
-L(L9:)
- movel R(a0),R(d0)
- movel MEM_POSTINC(sp),R(d3)
- movel MEM_POSTINC(sp),R(d2)
- rts
-END(strchr)
-
-weak_alias (strchr, index)
-libc_hidden_builtin_def (strchr)