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Diffstat (limited to 'sysdeps/m68k/memchr.S')
| -rw-r--r-- | sysdeps/m68k/memchr.S | 228 |
1 files changed, 228 insertions, 0 deletions
diff --git a/sysdeps/m68k/memchr.S b/sysdeps/m68k/memchr.S new file mode 100644 index 0000000000..a1599f8d89 --- /dev/null +++ b/sysdeps/m68k/memchr.S @@ -0,0 +1,228 @@ +/* memchr (str, ch, n) -- Return pointer to first occurrence of CH in the + first N bytes of STR. + For Motorola 68000. + Copyright (C) 1999 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 Library General Public License as + published by the Free Software Foundation; either version 2 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. 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(memchr) + /* Save the callee-saved registers we use. */ + moveml R(d2)-R(d4),MEM_PREDEC(sp) + + /* Get string pointer, character and length. */ + movel MEM_DISP(sp,16),R(a0) + moveb MEM_DISP(sp,23),R(d0) + movel MEM_DISP(sp,24),R(d4) + + /* Check if at least four bytes left to search. */ + moveql #4,R(d1) + cmpl R(d1),R(d4) + bcs L(L6) + + /* 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) + cmpb MEM(a0),R(d0) + beq L(L9) + addql #1,R(a0) + subql #1,R(d4) + beq L(L7) + + movel R(a0),R(d1) + andw #3,R(d1) + beq L(L1) + cmpb MEM(a0),R(d0) + beq L(L9) + addql #1,R(a0) + subql #1,R(d4) + beq L(L7) + + movel R(a0),R(d1) + andw #3,R(d1) + beq L(L1) + cmpb MEM(a0),R(d0) + beq L(L9) + addql #1,R(a0) + subql #1,R(d4) + beq L(L7) + +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. */ + + /* Still at least 4 bytes to search? */ + subql #4,R(d4) + bcs L(L6) + +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) + + /* Still at least 4 bytes to search? */ + subql #4,R(d4) + bcs L(L6) + + /* 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) + + /* Still at least 4 bytes to search? */ + subql #4,R(d4) + bcc L(L2) + +L(L6:) + /* Search one byte at a time in the remaining less than 4 bytes. */ + andw #3,R(d4) + beq L(L7) + cmpb MEM(a0),R(d0) + beq L(L9) + addql #1,R(a0) + + subqw #1,R(d4) + beq L(L7) + cmpb MEM(a0),R(d0) + beq L(L9) + addql #1,R(a0) + + subqw #1,R(d4) + beq L(L7) + cmpb MEM(a0),R(d0) + beq L(L9) + +L(L7:) + /* Return NULL. */ + clrl R(d0) + movel R(d0),R(a0) + moveml MEM_POSTINC(sp),R(d2)-R(d4) + 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) + + 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) + moveml MEM_POSTINC(sp),R(d2)-R(d4) + rts +END(strchr) + +weak_alias (strchr, index) |