1 1.5 skrll /* $NetBSD: ffs.S,v 1.5 2020/05/05 06:20:55 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 1.5 skrll 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
Indexes created Fri Oct 31 04:09:52 GMT 2025