1*2af01421Sskrll/* $NetBSD: ffs.S,v 1.5 2020/05/05 06:20:55 skrll Exp $ */ 202ac1ae2Sfredette 302ac1ae2Sfredette/* $OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $ */ 402ac1ae2Sfredette 502ac1ae2Sfredette/* 602ac1ae2Sfredette * Copyright (c) 1990, 1991, 1992, 1994, The University of Utah and 702ac1ae2Sfredette * the Computer Systems Laboratory at the University of Utah (CSL). 802ac1ae2Sfredette * All rights reserved. 902ac1ae2Sfredette * 1002ac1ae2Sfredette * Permission to use, copy, modify and distribute this software and its 1102ac1ae2Sfredette * documentation is hereby granted, provided that both the copyright 1202ac1ae2Sfredette * notice and this permission notice appear in all copies of the 1302ac1ae2Sfredette * software, derivative works or modified versions, and any portions 1402ac1ae2Sfredette * thereof, and that both notices appear in supporting documentation. 1502ac1ae2Sfredette * 1602ac1ae2Sfredette * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS 1702ac1ae2Sfredette * IS" CONDITION. THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF 1802ac1ae2Sfredette * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 1902ac1ae2Sfredette * 2002ac1ae2Sfredette * CSL requests users of this software to return to csl-dist@cs.utah.edu any 2102ac1ae2Sfredette * improvements that they make and grant CSL redistribution rights. 2202ac1ae2Sfredette * 2302ac1ae2Sfredette */ 2402ac1ae2Sfredette 2502ac1ae2Sfredette#include <machine/asm.h> 2602ac1ae2Sfredette 2702ac1ae2Sfredette#ifdef SYSLIBC_SCCS 2802ac1ae2Sfredette .text 2902ac1ae2Sfredette .asciz "$OpenBSD: ffs.S,v 1.3 2001/06/04 23:14:02 mickey Exp $" 3002ac1ae2Sfredette .align 4 3102ac1ae2Sfredette#endif 3202ac1ae2Sfredette 3302ac1ae2Sfredette/* 3402ac1ae2Sfredette * ffs(bitmask) 3502ac1ae2Sfredette * 3602ac1ae2Sfredette * Return the position of the "most significant" bit in `bitmask'. 3702ac1ae2Sfredette * Since this is similar to the VAX ffs instruction, bits in a word 3802ac1ae2Sfredette * are numbered as "32, 31, ... 1", 0 is returned if no bits are set. 3902ac1ae2Sfredette */ 4002ac1ae2Sfredette 4102ac1ae2SfredetteLEAF_ENTRY(ffs) 42ed9d4336Smatt comb,= %arg0,%r0,ffsdone ; If arg0 is 0 43ed9d4336Smatt or %r0,%r0,%ret0 ; return 0 44ed9d4336Smatt ldi 32,%ret0 ; Set return to high bit 45ed9d4336Smatt extru,= %arg0,31,16,%r0 ; If low 16 bits are non-zero 46ed9d4336Smatt addi,tr -16,%ret0,%ret0 ; subtract 16 from bitpos 47ed9d4336Smatt shd %r0,%arg0,16,%arg0 ; else shift right 16 bits 48ed9d4336Smatt extru,= %arg0,31,8,%r0 ; If low 8 bits are non-zero 49ed9d4336Smatt addi,tr -8,%ret0,%ret0 ; subtract 8 from bitpos 50ed9d4336Smatt shd %r0,%arg0,8,%arg0 ; else shift right 8 bits 51ed9d4336Smatt extru,= %arg0,31,4,%r0 ; If low 4 bits are non-zero 52ed9d4336Smatt addi,tr -4,%ret0,%ret0 ; subtract 4 from bitpos 53ed9d4336Smatt shd %r0,%arg0,4,%arg0 ; else shift right 4 bits 54ed9d4336Smatt extru,= %arg0,31,2,%r0 ; If low 2 bits are non-zero 55ed9d4336Smatt addi,tr -2,%ret0,%ret0 ; subtract 2 from bitpos 56ed9d4336Smatt shd %r0,%arg0,2,%arg0 ; else shift right 2 bits 57ed9d4336Smatt extru,= %arg0,31,1,%r0 ; If low bit is non-zero 58ed9d4336Smatt addi -1,%ret0,%ret0 ; subtract 1 from bitpos 5902ac1ae2Sfredetteffsdone: 607d976824Schs bv,n %r0(%rp) 6102ac1ae2SfredetteEXIT(ffs) 6202ac1ae2Sfredette 6302ac1ae2Sfredette .end 64