/* rawmemchr (str, ch) -- Return pointer to first occurrence of CH in STR. For Motorola 68000. Copyright (C) 1999-2016 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Andreas Schwab . 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, see . */ #include #include "asm-syntax.h" TEXT ENTRY(__rawmemchr) /* Save the callee-saved registers we use. */ movel R(d2),MEM_PREDEC(sp) cfi_adjust_cfa_offset (4) movel R(d3),MEM_PREDEC(sp) cfi_adjust_cfa_offset (4) cfi_rel_offset (R(d2), 4) cfi_rel_offset (R(d3), 0) /* 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) cfi_adjust_cfa_offset (-4) cfi_restore (R(d3)) movel MEM_POSTINC(sp),R(d2) cfi_adjust_cfa_offset (-4) cfi_restore (R(d2)) rts END(__rawmemchr) libc_hidden_def (__rawmemchr) weak_alias (__rawmemchr, rawmemchr)