177 lines
5.0 KiB
ArmAsm
177 lines
5.0 KiB
ArmAsm
/* Copyright (C) 1996, 2000, 2003 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by David Mosberger (davidm@cs.arizona.edu).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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/* Finds characters in a memory area. Optimized for the Alpha:
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- memory accessed as aligned quadwords only
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- uses cmpbge to compare 8 bytes in parallel
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- does binary search to find 0 byte in last
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quadword (HAKMEM needed 12 instructions to
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do this instead of the 9 instructions that
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binary search needs).
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For correctness consider that:
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- only minimum number of quadwords may be accessed
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- the third argument is an unsigned long
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*/
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#include <sysdep.h>
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.set noreorder
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.set noat
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ENTRY(__memchr)
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#ifdef PROF
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ldgp gp, 0(pv)
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lda AT, _mcount
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jsr AT, (AT), _mcount
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.prologue 1
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#else
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.prologue 0
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#endif
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# Hack -- if someone passes in (size_t)-1, hoping to just
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# search til the end of the address space, we will overflow
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# below when we find the address of the last byte. Given
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# that we will never have a 56-bit address space, cropping
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# the length is the easiest way to avoid trouble.
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zap a2, 0x80, t4 #-e0 :
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beq a2, $not_found # .. e1 :
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ldq_u t0, 0(a0) # e1 : load first quadword
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insbl a1, 1, t1 # .. e0 : t1 = 000000000000ch00
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and a1, 0xff, a1 #-e0 : a1 = 00000000000000ch
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cmpult a2, 9, t3 # .. e1 :
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or t1, a1, a1 # e0 : a1 = 000000000000chch
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lda t2, -1(zero) # .. e1 :
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sll a1, 16, t1 #-e0 : t1 = 00000000chch0000
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addq a0, t4, t4 # .. e1 :
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or t1, a1, a1 # e1 : a1 = 00000000chchchch
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unop # :
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sll a1, 32, t1 #-e0 : t1 = chchchch00000000
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or t1, a1, a1 # e1 : a1 = chchchchchchchch
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extql t0, a0, t6 # e0 :
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beq t3, $first_quad # .. e1 :
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ldq_u t5, -1(t4) #-e1 : eight or less bytes to search
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extqh t5, a0, t5 # .. e0 :
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mov a0, v0 # e0 :
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or t6, t5, t0 # .. e1 : t0 = quadword starting at a0
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# Deal with the case where at most 8 bytes remain to be searched
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# in t0. E.g.:
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# a2 = 6
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# t0 = ????c6c5c4c3c2c1
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$last_quad:
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negq a2, t5 #-e0 :
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xor a1, t0, t0 # .. e1 :
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srl t2, t5, t5 # e0 : t5 = mask of a2 bits set
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cmpbge zero, t0, t1 # .. e1 :
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and t1, t5, t1 #-e0 :
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beq t1, $not_found # .. e1 :
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$found_it:
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# Now, determine which byte matched:
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negq t1, t2 # e0 :
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and t1, t2, t1 # e1 :
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and t1, 0x0f, t0 #-e0 :
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addq v0, 4, t2 # .. e1 :
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cmoveq t0, t2, v0 # e0 :
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addq v0, 2, t2 # .. e1 :
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and t1, 0x33, t0 #-e0 :
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cmoveq t0, t2, v0 # .. e1 :
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and t1, 0x55, t0 # e0 :
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addq v0, 1, t2 # .. e1 :
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cmoveq t0, t2, v0 #-e0 :
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$done: ret # .. e1 :
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# Deal with the case where a2 > 8 bytes remain to be
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# searched. a0 may not be aligned.
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.align 4
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$first_quad:
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andnot a0, 0x7, v0 #-e1 :
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insqh t2, a0, t1 # .. e0 : t1 = 0000ffffffffffff (a0<0:2> ff)
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xor t0, a1, t0 # e0 :
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or t0, t1, t0 # e1 : t0 = ====ffffffffffff
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cmpbge zero, t0, t1 #-e0 :
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bne t1, $found_it # .. e1 :
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# At least one byte left to process.
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ldq t0, 8(v0) # e0 :
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subq t4, 1, a2 # .. e1 :
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addq v0, 8, v0 #-e0 :
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# Make a2 point to last quad to be accessed (the
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# last quad may or may not be partial).
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andnot a2, 0x7, a2 # .. e1 :
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cmpult v0, a2, t1 # e0 :
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beq t1, $final # .. e1 :
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# At least two quads remain to be accessed.
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subq a2, v0, t3 #-e0 : t3 <- nr quads to be processed
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and t3, 8, t3 # e1 : odd number of quads?
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bne t3, $odd_quad_count # e1 :
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# At least three quads remain to be accessed
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mov t0, t3 # e0 : move prefetched value to correct reg
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.align 4
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$unrolled_loop:
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ldq t0, 8(v0) #-e0 : prefetch t0
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xor a1, t3, t1 # .. e1 :
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cmpbge zero, t1, t1 # e0 :
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bne t1, $found_it # .. e1 :
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addq v0, 8, v0 #-e0 :
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$odd_quad_count:
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xor a1, t0, t1 # .. e1 :
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ldq t3, 8(v0) # e0 : prefetch t3
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cmpbge zero, t1, t1 # .. e1 :
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addq v0, 8, t5 #-e0 :
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bne t1, $found_it # .. e1 :
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cmpult t5, a2, t5 # e0 :
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addq v0, 8, v0 # .. e1 :
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bne t5, $unrolled_loop #-e1 :
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mov t3, t0 # e0 : move prefetched value into t0
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$final: subq t4, v0, a2 # .. e1 : a2 <- number of bytes left to do
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bne a2, $last_quad # e1 :
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$not_found:
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mov zero, v0 #-e0 :
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ret # .. e1 :
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END(__memchr)
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weak_alias (__memchr, memchr)
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#if !__BOUNDED_POINTERS__
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weak_alias (__memchr, __ubp_memchr)
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#endif
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libc_hidden_builtin_def (memchr)
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