Home | History | Annotate | Line # | Download | only in string
ffs.S revision 1.4 
      1  1.4     skrll /*	$NetBSD: ffs.S,v 1.4 2020/05/03 15:29:22 skrll Exp $	*/
      2  1.1  fredette 
      3  1.1  fredette /*	$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $	*/
      4  1.1  fredette 
      5  1.4     skrll /*
      6  1.1  fredette  * Copyright (c) 1990, 1991, 1992, 1994, The University of Utah and
      7  1.1  fredette  * the Computer Systems Laboratory at the University of Utah (CSL).
      8  1.1  fredette  * All rights reserved.
      9  1.1  fredette  *
     10  1.1  fredette  * Permission to use, copy, modify and distribute this software and its
     11  1.1  fredette  * documentation is hereby granted, provided that both the copyright
     12  1.1  fredette  * notice and this permission notice appear in all copies of the
     13  1.1  fredette  * software, derivative works or modified versions, and any portions
     14  1.1  fredette  * thereof, and that both notices appear in supporting documentation.
     15  1.1  fredette  *
     16  1.1  fredette  * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
     17  1.1  fredette  * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
     18  1.1  fredette  * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     19  1.1  fredette  *
     20  1.1  fredette  * CSL requests users of this software to return to csl-dist (at) cs.utah.edu any
     21  1.1  fredette  * improvements that they make and grant CSL redistribution rights.
     22  1.1  fredette  *
     23  1.1  fredette  */
     24  1.1  fredette 
     25  1.1  fredette #include <machine/asm.h>
     26  1.1  fredette 
     27  1.1  fredette #ifdef SYSLIBC_SCCS
     28  1.1  fredette 	.text
     29  1.1  fredette 	.asciz "$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $"
     30  1.1  fredette 	.align	4
     31  1.1  fredette #endif
     32  1.1  fredette 
     33  1.1  fredette /*
     34  1.1  fredette  * ffs(bitmask)
     35  1.1  fredette  *
     36  1.1  fredette  * Return the position of the "most significant" bit in `bitmask'.
     37  1.1  fredette  * Since this is similar to the VAX ffs instruction, bits in a word
     38  1.1  fredette  * are numbered as "32, 31, ... 1", 0 is returned if no bits are set.
     39  1.1  fredette  */
     40  1.1  fredette 
     41  1.1  fredette LEAF_ENTRY(ffs)
     42  1.2      matt 	comb,=	%arg0,%r0,ffsdone	; If arg0 is 0
     43  1.2      matt 	or	%r0,%r0,%ret0		;   return 0
     44  1.2      matt 	ldi	32,%ret0		; Set return to high bit
     45  1.2      matt 	extru,=	%arg0,31,16,%r0		; If low 16 bits are non-zero
     46  1.2      matt 	addi,tr	-16,%ret0,%ret0		;   subtract 16 from bitpos
     47  1.2      matt 	shd	%r0,%arg0,16,%arg0	; else shift right 16 bits
     48  1.2      matt 	extru,=	%arg0,31,8,%r0		; If low 8 bits are non-zero
     49  1.2      matt 	addi,tr	-8,%ret0,%ret0		;   subtract 8 from bitpos
     50  1.2      matt 	shd	%r0,%arg0,8,%arg0	; else shift right 8 bits
     51  1.2      matt 	extru,=	%arg0,31,4,%r0		; If low 4 bits are non-zero
     52  1.2      matt 	addi,tr	-4,%ret0,%ret0		;   subtract 4 from bitpos
     53  1.2      matt 	shd	%r0,%arg0,4,%arg0	; else shift right 4 bits
     54  1.2      matt 	extru,=	%arg0,31,2,%r0		; If low 2 bits are non-zero
     55  1.2      matt 	addi,tr	-2,%ret0,%ret0		;   subtract 2 from bitpos
     56  1.2      matt 	shd	%r0,%arg0,2,%arg0	; else shift right 2 bits
     57  1.2      matt 	extru,=	%arg0,31,1,%r0		; If low bit is non-zero
     58  1.2      matt 	addi	-1,%ret0,%ret0		;   subtract 1 from bitpos
     59  1.1  fredette ffsdone:
     60  1.3       chs 	bv,n	%r0(%rp)
     61  1.1  fredette EXIT(ffs)
     62  1.1  fredette 
     63  1.1  fredette 	.end
     64