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-rw-r--r--sysdeps/m68k/strchr.S257
1 files changed, 257 insertions, 0 deletions
diff --git a/sysdeps/m68k/strchr.S b/sysdeps/m68k/strchr.S
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+++ b/sysdeps/m68k/strchr.S
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+/* strchr (str, ch) -- Return pointer to first occurrence of CH in 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(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)
generated by cgit-pink 1.4.1 (git 2.36.1) at 2024-11-04 04:55:56 +0000