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73 lines
1.8 KiB
ArmAsm
73 lines
1.8 KiB
ArmAsm
/* Copyright (C) 1996, 1997 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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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/* Finds the first bit set in an integer. Optimized for the Alpha
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architecture. */
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#include <sysdep.h>
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.set noreorder
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.set noat
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ENTRY(ffs)
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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 zero, 0(sp) # on the 21064, this helps dual-issuing
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addl a0, zero, a0 # the last insn and reduces the stall
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negq a0, t0 # due to the srl instruction
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and a0, t0, t0
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clr v0
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beq a0, $done
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# now do binary search for first non-zero bit
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zapnot t0, 0x03, t2
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addq v0, 16, t3
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cmoveq t2, t3, v0
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zapnot t0, 0x05, t2
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addq v0, 8, t3
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cmoveq t2, t3, v0
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srl t0, v0, t0
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addq v0, 1, v0
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and t0, 0x0f, t2
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addq v0, 4, t3
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cmoveq t2, t3, v0
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and t0, 0x33, t2
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addq v0, 2, t3
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cmoveq t2, t3, v0
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and t0, 0x55, t2
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addq v0, 1, t3
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cmoveq t2, t3, v0
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$done: ret
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END(ffs)
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