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-/* memchr (str, ch, n) -- Return pointer to first occurrence of CH in the
-   first N bytes of STR.
-   For Motorola 68000.
-   Copyright (C) 1999, 2000, 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(__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(__memchr)
-
-weak_alias (__memchr, memchr)
-#if !__BOUNDED_POINTERS__
-weak_alias (__memchr, __ubp_memchr)
-#endif
-libc_hidden_builtin_def (memchr)
generated by cgit-pink 1.4.1 (git 2.36.1) at 2024-11-05 14:01:51 +0000