11dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project/* $NetBSD: ffs.S,v 1.5 2003/04/05 23:08:52 bjh21 Exp $ */ 21dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project/* 31dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * Copyright (c) 2001 Christopher Gilbert 41dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * All rights reserved. 51dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 61dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * Redistribution and use in source and binary forms, with or without 71dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * modification, are permitted provided that the following conditions 81dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * are met: 91dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 1. Redistributions of source code must retain the above copyright 101dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * notice, this list of conditions and the following disclaimer. 111dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 2. Redistributions in binary form must reproduce the above copyright 121dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * notice, this list of conditions and the following disclaimer in the 131dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * documentation and/or other materials provided with the distribution. 141dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 3. The name of the company nor the name of the author may be used to 151dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * endorse or promote products derived from this software without specific 161dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * prior written permission. 171dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 181dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 191dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 201dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 211dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 221dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 231dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 241dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 251dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 261dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 271dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 281dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * SUCH DAMAGE. 291dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project */ 301dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 311dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project#include <machine/asm.h> 321dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 331dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project/* 341dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * ffs - find first set bit, this algorithm isolates the first set 351dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * bit, then multiplies the number by 0x0450fbaf which leaves the top 361dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 6 bits as an index into the table. This algorithm should be a win 371dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * over the checking each bit in turn as per the C compiled version. 381dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 391dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * under ARMv5 there's an instruction called CLZ (count leading Zero's) that 401dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * could be used 411dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 421dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on 431dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * 16 Feb 1994. 441dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project */ 451dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 461dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source ProjectENTRY(ffs) 471dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project /* Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry */ 481dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project rsb r1, r0, #0 491dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project ands r0, r0, r1 501dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project#ifndef __ARM_ARCH_5__ 511dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project /* 521dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * now r0 has at most one set bit, call this X 531dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project * if X = 0, all further instructions are skipped 541dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project */ 551dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project adrne r2, .L_ffs_table 561dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project orrne r0, r0, r0, lsl #4 /* r0 = X * 0x11 */ 571dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project orrne r0, r0, r0, lsl #6 /* r0 = X * 0x451 */ 581dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project rsbne r0, r0, r0, lsl #16 /* r0 = X * 0x0450fbaf */ 591dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 601dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project /* now lookup in table indexed on top 6 bits of r0 */ 611dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project ldrneb r0, [ r2, r0, lsr #26 ] 621dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 631dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project bx lr 641dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 651dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project.text; 661dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project.type .L_ffs_table, _ASM_TYPE_OBJECT; 671dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project.L_ffs_table: 681dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project/* 0 1 2 3 4 5 6 7 */ 691dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 0, 1, 2, 13, 3, 7, 0, 14 /* 0- 7 */ 701dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 4, 0, 8, 0, 0, 0, 0, 15 /* 8-15 */ 711dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 11, 5, 0, 0, 9, 0, 0, 26 /* 16-23 */ 721dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 0, 0, 0, 0, 0, 22, 28, 16 /* 24-31 */ 731dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 32, 12, 6, 0, 0, 0, 0, 0 /* 32-39 */ 741dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 10, 0, 0, 25, 0, 0, 21, 27 /* 40-47 */ 751dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 31, 0, 0, 0, 0, 24, 0, 20 /* 48-55 */ 761dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project .byte 30, 0, 23, 19, 29, 18, 17, 0 /* 56-63 */ 771dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project#else 781dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project clzne r0, r0 791dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project rsbne r0, r0, #32 801dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project bx lr 811dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project#endif 821dc9e472e19acfe6dc7f41e429236e7eef7ceda1The Android Open Source Project 83