77 lines
2.1 KiB
ArmAsm
77 lines
2.1 KiB
ArmAsm
/* Copyright (C) 1996-2014 Free Software Foundation, Inc.
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Contributed by David Mosberger (davidm@cs.arizona.edu).
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This file is part of the GNU C Library.
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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, see
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<http://www.gnu.org/licenses/>. */
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/* Finds length of a 0-terminated string. Optimized for the Alpha
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architecture:
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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 quadword (HAKMEM
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needed 12 instructions to do this instead of the 8 instructions
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that the binary search needs).
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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(strlen)
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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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ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned)
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lda t1, -1(zero)
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insqh t1, a0, t1
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andnot a0, 7, v0
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or t1, t0, t0
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nop # dual issue the next two on ev5
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cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0
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bne t1, $found
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$loop: ldq t0, 8(v0)
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addq v0, 8, v0 # addr += 8
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cmpbge zero, t0, t1
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beq t1, $loop
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$found: negq t1, t2 # clear all but least set bit
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and t1, t2, t1
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and t1, 0xf0, t2 # binary search for that set bit
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and t1, 0xcc, t3
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and t1, 0xaa, t4
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cmovne t2, 4, t2
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cmovne t3, 2, t3
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cmovne t4, 1, t4
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addq t2, t3, t2
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addq v0, t4, v0
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addq v0, t2, v0
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nop # dual issue next two on ev4 and ev5
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subq v0, a0, v0
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ret
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END(strlen)
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libc_hidden_builtin_def (strlen)
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