| /* rawmemchr (str, ch) -- Return pointer to first occurrence of CH in STR. |
| For Motorola 68000. |
| Copyright (C) 1999, 2002 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(__rawmemchr) |
| /* 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) |
| #ifdef __mcoldfire__ |
| andl #3,R(d1) |
| #else |
| andw #3,R(d1) |
| #endif |
| beq L(L1) |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| addql #1,R(a0) |
| |
| #ifdef __mcoldfire__ |
| subql #3,R(d1) |
| #else |
| subqw #3,R(d1) |
| #endif |
| beq L(L1) |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| addql #1,R(a0) |
| |
| #ifdef __mcoldfire__ |
| addql #1,R(d1) |
| #else |
| addqw #1,R(d1) |
| #endif |
| beq L(L1) |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| 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) |
| |
| /* 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. */ |
| beq L(L2) |
| |
| 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) |
| |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| addql #1,R(a0) |
| |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| addql #1,R(a0) |
| |
| cmpb MEM(a0),R(d0) |
| beq L(L9) |
| 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(__rawmemchr) |
| |
| libc_hidden_def (__rawmemchr) |
| weak_alias (__rawmemchr, rawmemchr) |
