64 lines
2.2 KiB
ArmAsm
64 lines
2.2 KiB
ArmAsm
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/* $NetBSD: ffs.S,v 1.3 2004/07/18 20:30:04 chs Exp $ */
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/* $OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $ */
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/*
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* Copyright (c) 1990, 1991, 1992, 1994, The University of Utah and
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* the Computer Systems Laboratory at the University of Utah (CSL).
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* All rights reserved.
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*
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* Permission to use, copy, modify and distribute this software and its
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* documentation is hereby granted, provided that both the copyright
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* notice and this permission notice appear in all copies of the
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* software, derivative works or modified versions, and any portions
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* thereof, and that both notices appear in supporting documentation.
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*
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* THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
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* IS" CONDITION. THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
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* ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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*
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* CSL requests users of this software to return to csl-dist@cs.utah.edu any
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* improvements that they make and grant CSL redistribution rights.
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*
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*/
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#include <machine/asm.h>
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#ifdef SYSLIBC_SCCS
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.text
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.asciz "$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $"
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.align 4
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#endif
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/*
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* ffs(bitmask)
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*
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* Return the position of the "most significant" bit in `bitmask'.
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* Since this is similar to the VAX ffs instruction, bits in a word
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* are numbered as "32, 31, ... 1", 0 is returned if no bits are set.
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*/
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LEAF_ENTRY(ffs)
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comb,= %arg0,%r0,ffsdone ; If arg0 is 0
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or %r0,%r0,%ret0 ; return 0
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ldi 32,%ret0 ; Set return to high bit
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extru,= %arg0,31,16,%r0 ; If low 16 bits are non-zero
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addi,tr -16,%ret0,%ret0 ; subtract 16 from bitpos
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shd %r0,%arg0,16,%arg0 ; else shift right 16 bits
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extru,= %arg0,31,8,%r0 ; If low 8 bits are non-zero
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addi,tr -8,%ret0,%ret0 ; subtract 8 from bitpos
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shd %r0,%arg0,8,%arg0 ; else shift right 8 bits
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extru,= %arg0,31,4,%r0 ; If low 4 bits are non-zero
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addi,tr -4,%ret0,%ret0 ; subtract 4 from bitpos
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shd %r0,%arg0,4,%arg0 ; else shift right 4 bits
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extru,= %arg0,31,2,%r0 ; If low 2 bits are non-zero
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addi,tr -2,%ret0,%ret0 ; subtract 2 from bitpos
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shd %r0,%arg0,2,%arg0 ; else shift right 2 bits
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extru,= %arg0,31,1,%r0 ; If low bit is non-zero
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addi -1,%ret0,%ret0 ; subtract 1 from bitpos
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ffsdone:
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bv,n %r0(%rp)
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EXIT(ffs)
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.end
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