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/arch/alpha/lib/memchr.S

http://github.com/mirrors/linux
Assembly | 165 lines | 133 code | 32 blank | 0 comment | 3 complexity | fadc9cb1c9b5dce0845c9e03280f7bb1 MD5 | raw file
  1/* Copyright (C) 1996 Free Software Foundation, Inc.
  2   This file is part of the GNU C Library.
  3   Contributed by David Mosberger (davidm@cs.arizona.edu).
  4
  5   The GNU C Library is free software; you can redistribute it and/or
  6   modify it under the terms of the GNU Library General Public License as
  7   published by the Free Software Foundation; either version 2 of the
  8   License, or (at your option) any later version.
  9
 10   The GNU C Library is distributed in the hope that it will be useful,
 11   but WITHOUT ANY WARRANTY; without even the implied warranty of
 12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 13   Library General Public License for more details.
 14
 15   You should have received a copy of the GNU Library General Public
 16   License along with the GNU C Library; see the file COPYING.LIB.  If not,
 17   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 18   Boston, MA 02111-1307, USA.  */
 19
 20/* Finds characters in a memory area.  Optimized for the Alpha:
 21
 22      - memory accessed as aligned quadwords only
 23      - uses cmpbge to compare 8 bytes in parallel
 24      - does binary search to find 0 byte in last
 25        quadword (HAKMEM needed 12 instructions to
 26        do this instead of the 9 instructions that
 27        binary search needs).
 28
 29For correctness consider that:
 30
 31      - only minimum number of quadwords may be accessed
 32      - the third argument is an unsigned long
 33*/
 34#include <asm/export.h>
 35        .set noreorder
 36        .set noat
 37
 38	.globl memchr
 39	.ent memchr
 40memchr:
 41	.frame $30,0,$26,0
 42	.prologue 0
 43
 44	# Hack -- if someone passes in (size_t)-1, hoping to just
 45	# search til the end of the address space, we will overflow
 46	# below when we find the address of the last byte.  Given
 47	# that we will never have a 56-bit address space, cropping
 48	# the length is the easiest way to avoid trouble.
 49	zap	$18, 0x80, $5	#-e0	:
 50
 51	beq	$18, $not_found	# .. e1 :
 52        ldq_u   $1, 0($16)	# e1	: load first quadword
 53	insbl	$17, 1, $2	# .. e0 : $2 = 000000000000ch00
 54	and	$17, 0xff, $17	#-e0    : $17 = 00000000000000ch
 55	cmpult	$18, 9, $4	# .. e1 :
 56	or	$2, $17, $17	# e0    : $17 = 000000000000chch
 57        lda     $3, -1($31)	# .. e1 :
 58	sll	$17, 16, $2	#-e0    : $2 = 00000000chch0000
 59	addq	$16, $5, $5	# .. e1 :
 60	or	$2, $17, $17	# e1    : $17 = 00000000chchchch
 61	unop			#	:
 62	sll	$17, 32, $2	#-e0    : $2 = chchchch00000000
 63	or	$2, $17, $17	# e1	: $17 = chchchchchchchch
 64	extql	$1, $16, $7	# e0    : 
 65	beq	$4, $first_quad	# .. e1 :
 66
 67	ldq_u	$6, -1($5)	#-e1	: eight or less bytes to search
 68	extqh	$6, $16, $6	# .. e0 :
 69	mov	$16, $0		# e0	:
 70	or	$7, $6, $1	# .. e1 : $1 = quadword starting at $16
 71
 72	# Deal with the case where at most 8 bytes remain to be searched
 73	# in $1.  E.g.:
 74	#	$18 = 6
 75	#	$1 = ????c6c5c4c3c2c1
 76$last_quad:
 77	negq	$18, $6		#-e0	:
 78        xor	$17, $1, $1	# .. e1 :
 79	srl	$3, $6, $6	# e0    : $6 = mask of $18 bits set
 80        cmpbge  $31, $1, $2	# .. e1 :
 81	and	$2, $6, $2	#-e0	:
 82        beq     $2, $not_found	# .. e1 :
 83
 84$found_it:
 85	# Now, determine which byte matched:
 86        negq    $2, $3		# e0	:
 87        and     $2, $3, $2	# e1	:
 88
 89        and     $2, 0x0f, $1	#-e0	:
 90        addq    $0, 4, $3	# .. e1 :
 91        cmoveq  $1, $3, $0	# e0	:
 92
 93        addq    $0, 2, $3	# .. e1 :
 94        and     $2, 0x33, $1	#-e0	:
 95        cmoveq  $1, $3, $0	# .. e1 :
 96
 97        and     $2, 0x55, $1	# e0	:
 98        addq    $0, 1, $3	# .. e1 :
 99        cmoveq  $1, $3, $0	#-e0	:
100
101$done:	ret			# .. e1 :
102
103	# Deal with the case where $18 > 8 bytes remain to be
104	# searched.  $16 may not be aligned.
105	.align 4
106$first_quad:
107	andnot	$16, 0x7, $0	#-e1	:
108        insqh   $3, $16, $2	# .. e0	: $2 = 0000ffffffffffff ($16<0:2> ff)
109        xor	$1, $17, $1	# e0	:
110	or	$1, $2, $1	# e1	: $1 = ====ffffffffffff
111        cmpbge  $31, $1, $2	#-e0	:
112        bne     $2, $found_it	# .. e1 :
113
114	# At least one byte left to process.
115
116	ldq	$1, 8($0)	# e0	:
117	subq	$5, 1, $18	# .. e1 :
118	addq	$0, 8, $0	#-e0	:
119
120	# Make $18 point to last quad to be accessed (the
121	# last quad may or may not be partial).
122
123	andnot	$18, 0x7, $18	# .. e1 :
124	cmpult	$0, $18, $2	# e0	:
125	beq	$2, $final	# .. e1 :
126
127	# At least two quads remain to be accessed.
128
129	subq	$18, $0, $4	#-e0	: $4 <- nr quads to be processed
130	and	$4, 8, $4	# e1	: odd number of quads?
131	bne	$4, $odd_quad_count # e1 :
132
133	# At least three quads remain to be accessed
134
135	mov	$1, $4		# e0	: move prefetched value to correct reg
136
137	.align	4
138$unrolled_loop:
139	ldq	$1, 8($0)	#-e0	: prefetch $1
140	xor	$17, $4, $2	# .. e1 :
141	cmpbge	$31, $2, $2	# e0	:
142	bne	$2, $found_it	# .. e1 :
143
144	addq	$0, 8, $0	#-e0	:
145$odd_quad_count:
146	xor	$17, $1, $2	# .. e1 :
147	ldq	$4, 8($0)	# e0	: prefetch $4
148	cmpbge	$31, $2, $2	# .. e1 :
149	addq	$0, 8, $6	#-e0	:
150	bne	$2, $found_it	# .. e1	:
151
152	cmpult	$6, $18, $6	# e0	:
153	addq	$0, 8, $0	# .. e1 :
154	bne	$6, $unrolled_loop #-e1 :
155
156	mov	$4, $1		# e0	: move prefetched value into $1
157$final:	subq	$5, $0, $18	# .. e1	: $18 <- number of bytes left to do
158	bne	$18, $last_quad	# e1	:
159
160$not_found:
161	mov	$31, $0		#-e0	:
162	ret			# .. e1 :
163
164        .end memchr
165	EXPORT_SYMBOL(memchr)