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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/alpha/lib/memchr.S
downloadlinux-stericsson-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+/* Copyright (C) 1996 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by David Mosberger (davidm@cs.arizona.edu).
+
+ 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. */
+
+/* Finds characters in a memory area. Optimized for the Alpha:
+
+ - memory accessed as aligned quadwords only
+ - uses cmpbge to compare 8 bytes in parallel
+ - does binary search to find 0 byte in last
+ quadword (HAKMEM needed 12 instructions to
+ do this instead of the 9 instructions that
+ binary search needs).
+
+For correctness consider that:
+
+ - only minimum number of quadwords may be accessed
+ - the third argument is an unsigned long
+*/
+
+ .set noreorder
+ .set noat
+
+ .globl memchr
+ .ent memchr
+memchr:
+ .frame $30,0,$26,0
+ .prologue 0
+
+ # Hack -- if someone passes in (size_t)-1, hoping to just
+ # search til the end of the address space, we will overflow
+ # below when we find the address of the last byte. Given
+ # that we will never have a 56-bit address space, cropping
+ # the length is the easiest way to avoid trouble.
+ zap $18, 0x80, $5 #-e0 :
+
+ beq $18, $not_found # .. e1 :
+ ldq_u $1, 0($16) # e1 : load first quadword
+ insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00
+ and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch
+ cmpult $18, 9, $4 # .. e1 :
+ or $2, $17, $17 # e0 : $17 = 000000000000chch
+ lda $3, -1($31) # .. e1 :
+ sll $17, 16, $2 #-e0 : $2 = 00000000chch0000
+ addq $16, $5, $5 # .. e1 :
+ or $2, $17, $17 # e1 : $17 = 00000000chchchch
+ unop # :
+ sll $17, 32, $2 #-e0 : $2 = chchchch00000000
+ or $2, $17, $17 # e1 : $17 = chchchchchchchch
+ extql $1, $16, $7 # e0 :
+ beq $4, $first_quad # .. e1 :
+
+ ldq_u $6, -1($5) #-e1 : eight or less bytes to search
+ extqh $6, $16, $6 # .. e0 :
+ mov $16, $0 # e0 :
+ or $7, $6, $1 # .. e1 : $1 = quadword starting at $16
+
+ # Deal with the case where at most 8 bytes remain to be searched
+ # in $1. E.g.:
+ # $18 = 6
+ # $1 = ????c6c5c4c3c2c1
+$last_quad:
+ negq $18, $6 #-e0 :
+ xor $17, $1, $1 # .. e1 :
+ srl $3, $6, $6 # e0 : $6 = mask of $18 bits set
+ cmpbge $31, $1, $2 # .. e1 :
+ and $2, $6, $2 #-e0 :
+ beq $2, $not_found # .. e1 :
+
+$found_it:
+ # Now, determine which byte matched:
+ negq $2, $3 # e0 :
+ and $2, $3, $2 # e1 :
+
+ and $2, 0x0f, $1 #-e0 :
+ addq $0, 4, $3 # .. e1 :
+ cmoveq $1, $3, $0 # e0 :
+
+ addq $0, 2, $3 # .. e1 :
+ and $2, 0x33, $1 #-e0 :
+ cmoveq $1, $3, $0 # .. e1 :
+
+ and $2, 0x55, $1 # e0 :
+ addq $0, 1, $3 # .. e1 :
+ cmoveq $1, $3, $0 #-e0 :
+
+$done: ret # .. e1 :
+
+ # Deal with the case where $18 > 8 bytes remain to be
+ # searched. $16 may not be aligned.
+ .align 4
+$first_quad:
+ andnot $16, 0x7, $0 #-e1 :
+ insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff)
+ xor $1, $17, $1 # e0 :
+ or $1, $2, $1 # e1 : $1 = ====ffffffffffff
+ cmpbge $31, $1, $2 #-e0 :
+ bne $2, $found_it # .. e1 :
+
+ # At least one byte left to process.
+
+ ldq $1, 8($0) # e0 :
+ subq $5, 1, $18 # .. e1 :
+ addq $0, 8, $0 #-e0 :
+
+ # Make $18 point to last quad to be accessed (the
+ # last quad may or may not be partial).
+
+ andnot $18, 0x7, $18 # .. e1 :
+ cmpult $0, $18, $2 # e0 :
+ beq $2, $final # .. e1 :
+
+ # At least two quads remain to be accessed.
+
+ subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed
+ and $4, 8, $4 # e1 : odd number of quads?
+ bne $4, $odd_quad_count # e1 :
+
+ # At least three quads remain to be accessed
+
+ mov $1, $4 # e0 : move prefetched value to correct reg
+
+ .align 4
+$unrolled_loop:
+ ldq $1, 8($0) #-e0 : prefetch $1
+ xor $17, $4, $2 # .. e1 :
+ cmpbge $31, $2, $2 # e0 :
+ bne $2, $found_it # .. e1 :
+
+ addq $0, 8, $0 #-e0 :
+$odd_quad_count:
+ xor $17, $1, $2 # .. e1 :
+ ldq $4, 8($0) # e0 : prefetch $4
+ cmpbge $31, $2, $2 # .. e1 :
+ addq $0, 8, $6 #-e0 :
+ bne $2, $found_it # .. e1 :
+
+ cmpult $6, $18, $6 # e0 :
+ addq $0, 8, $0 # .. e1 :
+ bne $6, $unrolled_loop #-e1 :
+
+ mov $4, $1 # e0 : move prefetched value into $1
+$final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do
+ bne $18, $last_quad # e1 :
+
+$not_found:
+ mov $31, $0 #-e0 :
+ ret # .. e1 :
+
+ .end memchr