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/* Copyright (C) 1996 Free Software Foundation, Inc.
Contributed by David Mosberger (davidm@cs.arizona.edu).
This file is part of the GNU C Library.
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., 675 Mass Ave,
Cambridge, MA 02139, USA. */
/* Finds length of a 0-terminated string. Optimized for the Alpha
architecture:
- 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 8 instructions
that the binary search needs).
*/
#include <sysdep.h>
.set noreorder
.set noat
ENTRY(strlen)
ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned)
lda t1, -1(zero)
insqh t1, a0, t1
andnot a0, 7, v0
or t1, t0, t0
nop # dual issue the next two on ev5
cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0
bne t1, $found
$loop: ldq t0, 8(v0)
addq v0, 8, v0 # addr += 8
cmpbge zero, t0, t1
beq t1, $loop
$found: negq t1, t2 # clear all but least set bit
and t1, t2, t1
and t1, 0xf0, t2 # binary search for that set bit
and t1, 0xcc, t3
and t1, 0xaa, t4
cmovne t2, 4, t2
cmovne t3, 2, t3
cmovne t4, 1, t4
addq t2, t3, t2
addq v0, t4, v0
addq v0, t2, v0
nop # dual issue next two on ev4 and ev5
subq v0, a0, v0
ret
END(strlen)
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