1/* 2 * linux/arch/arm/lib/lib1funcs.S: Optimized ARM division routines 3 * 4 * Author: Nicolas Pitre <nico@cam.org> 5 * - contributed to gcc-3.4 on Sep 30, 2003 6 * - adapted for the Linux kernel on Oct 2, 2003 7 */ 8 9/* Copyright 1995, 1996, 1998, 1999, 2000, 2003 Free Software Foundation, Inc. 10 11This file is free software; you can redistribute it and/or modify it 12under the terms of the GNU General Public License as published by the 13Free Software Foundation; either version 2, or (at your option) any 14later version. 15 16In addition to the permissions in the GNU General Public License, the 17Free Software Foundation gives you unlimited permission to link the 18compiled version of this file into combinations with other programs, 19and to distribute those combinations without any restriction coming 20from the use of this file. (The General Public License restrictions 21do apply in other respects; for example, they cover modification of 22the file, and distribution when not linked into a combine 23executable.) 24 25This file is distributed in the hope that it will be useful, but 26WITHOUT ANY WARRANTY; without even the implied warranty of 27MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 28General Public License for more details. 29 30You should have received a copy of the GNU General Public License 31along with this program; see the file COPYING. If not, write to 32the Free Software Foundation, 59 Temple Place - Suite 330, 33Boston, MA 02111-1307, USA. */ 34 35 36#include <linux/linkage.h> 37#include <asm/assembler.h> 38 39 40.macro ARM_DIV_BODY dividend, divisor, result, curbit 41 42#if __LINUX_ARM_ARCH__ >= 5 43 44 clz \curbit, \divisor 45 clz \result, \dividend 46 sub \result, \curbit, \result 47 mov \curbit, #1 48 mov \divisor, \divisor, lsl \result 49 mov \curbit, \curbit, lsl \result 50 mov \result, #0 51 52#else 53 54 @ Initially shift the divisor left 3 bits if possible, 55 @ set curbit accordingly. This allows for curbit to be located 56 @ at the left end of each 4 bit nibbles in the division loop 57 @ to save one loop in most cases. 58 tst \divisor, #0xe0000000 59 moveq \divisor, \divisor, lsl #3 60 moveq \curbit, #8 61 movne \curbit, #1 62 63 @ Unless the divisor is very big, shift it up in multiples of 64 @ four bits, since this is the amount of unwinding in the main 65 @ division loop. Continue shifting until the divisor is 66 @ larger than the dividend. 671: cmp \divisor, #0x10000000 68 cmplo \divisor, \dividend 69 movlo \divisor, \divisor, lsl #4 70 movlo \curbit, \curbit, lsl #4 71 blo 1b 72 73 @ For very big divisors, we must shift it a bit at a time, or 74 @ we will be in danger of overflowing. 751: cmp \divisor, #0x80000000 76 cmplo \divisor, \dividend 77 movlo \divisor, \divisor, lsl #1 78 movlo \curbit, \curbit, lsl #1 79 blo 1b 80 81 mov \result, #0 82 83#endif 84 85 @ Division loop 861: cmp \dividend, \divisor 87 subhs \dividend, \dividend, \divisor 88 orrhs \result, \result, \curbit 89 cmp \dividend, \divisor, lsr #1 90 subhs \dividend, \dividend, \divisor, lsr #1 91 orrhs \result, \result, \curbit, lsr #1 92 cmp \dividend, \divisor, lsr #2 93 subhs \dividend, \dividend, \divisor, lsr #2 94 orrhs \result, \result, \curbit, lsr #2 95 cmp \dividend, \divisor, lsr #3 96 subhs \dividend, \dividend, \divisor, lsr #3 97 orrhs \result, \result, \curbit, lsr #3 98 cmp \dividend, #0 @ Early termination? 99 movnes \curbit, \curbit, lsr #4 @ No, any more bits to do? 100 movne \divisor, \divisor, lsr #4 101 bne 1b 102 103.endm 104 105 106.macro ARM_DIV2_ORDER divisor, order 107 108#if __LINUX_ARM_ARCH__ >= 5 109 110 clz \order, \divisor 111 rsb \order, \order, #31 112 113#else 114 115 cmp \divisor, #(1 << 16) 116 movhs \divisor, \divisor, lsr #16 117 movhs \order, #16 118 movlo \order, #0 119 120 cmp \divisor, #(1 << 8) 121 movhs \divisor, \divisor, lsr #8 122 addhs \order, \order, #8 123 124 cmp \divisor, #(1 << 4) 125 movhs \divisor, \divisor, lsr #4 126 addhs \order, \order, #4 127 128 cmp \divisor, #(1 << 2) 129 addhi \order, \order, #3 130 addls \order, \order, \divisor, lsr #1 131 132#endif 133 134.endm 135 136 137.macro ARM_MOD_BODY dividend, divisor, order, spare 138 139#if __LINUX_ARM_ARCH__ >= 5 140 141 clz \order, \divisor 142 clz \spare, \dividend 143 sub \order, \order, \spare 144 mov \divisor, \divisor, lsl \order 145 146#else 147 148 mov \order, #0 149 150 @ Unless the divisor is very big, shift it up in multiples of 151 @ four bits, since this is the amount of unwinding in the main 152 @ division loop. Continue shifting until the divisor is 153 @ larger than the dividend. 1541: cmp \divisor, #0x10000000 155 cmplo \divisor, \dividend 156 movlo \divisor, \divisor, lsl #4 157 addlo \order, \order, #4 158 blo 1b 159 160 @ For very big divisors, we must shift it a bit at a time, or 161 @ we will be in danger of overflowing. 1621: cmp \divisor, #0x80000000 163 cmplo \divisor, \dividend 164 movlo \divisor, \divisor, lsl #1 165 addlo \order, \order, #1 166 blo 1b 167 168#endif 169 170 @ Perform all needed substractions to keep only the reminder. 171 @ Do comparisons in batch of 4 first. 172 subs \order, \order, #3 @ yes, 3 is intended here 173 blt 2f 174 1751: cmp \dividend, \divisor 176 subhs \dividend, \dividend, \divisor 177 cmp \dividend, \divisor, lsr #1 178 subhs \dividend, \dividend, \divisor, lsr #1 179 cmp \dividend, \divisor, lsr #2 180 subhs \dividend, \dividend, \divisor, lsr #2 181 cmp \dividend, \divisor, lsr #3 182 subhs \dividend, \dividend, \divisor, lsr #3 183 cmp \dividend, #1 184 mov \divisor, \divisor, lsr #4 185 subges \order, \order, #4 186 bge 1b 187 188 tst \order, #3 189 teqne \dividend, #0 190 beq 5f 191 192 @ Either 1, 2 or 3 comparison/substractions are left. 1932: cmn \order, #2 194 blt 4f 195 beq 3f 196 cmp \dividend, \divisor 197 subhs \dividend, \dividend, \divisor 198 mov \divisor, \divisor, lsr #1 1993: cmp \dividend, \divisor 200 subhs \dividend, \dividend, \divisor 201 mov \divisor, \divisor, lsr #1 2024: cmp \dividend, \divisor 203 subhs \dividend, \dividend, \divisor 2045: 205.endm 206 207 208ENTRY(__udivsi3) 209 210 subs r2, r1, #1 211 moveq pc, lr 212 bcc Ldiv0 213 cmp r0, r1 214 bls 11f 215 tst r1, r2 216 beq 12f 217 218 ARM_DIV_BODY r0, r1, r2, r3 219 220 mov r0, r2 221 mov pc, lr 222 22311: moveq r0, #1 224 movne r0, #0 225 mov pc, lr 226 22712: ARM_DIV2_ORDER r1, r2 228 229 mov r0, r0, lsr r2 230 mov pc, lr 231 232 233ENTRY(__umodsi3) 234 235 subs r2, r1, #1 @ compare divisor with 1 236 bcc Ldiv0 237 cmpne r0, r1 @ compare dividend with divisor 238 moveq r0, #0 239 tsthi r1, r2 @ see if divisor is power of 2 240 andeq r0, r0, r2 241 movls pc, lr 242 243 ARM_MOD_BODY r0, r1, r2, r3 244 245 mov pc, lr 246 247 248ENTRY(__divsi3) 249 250 cmp r1, #0 251 eor ip, r0, r1 @ save the sign of the result. 252 beq Ldiv0 253 rsbmi r1, r1, #0 @ loops below use unsigned. 254 subs r2, r1, #1 @ division by 1 or -1 ? 255 beq 10f 256 movs r3, r0 257 rsbmi r3, r0, #0 @ positive dividend value 258 cmp r3, r1 259 bls 11f 260 tst r1, r2 @ divisor is power of 2 ? 261 beq 12f 262 263 ARM_DIV_BODY r3, r1, r0, r2 264 265 cmp ip, #0 266 rsbmi r0, r0, #0 267 mov pc, lr 268 26910: teq ip, r0 @ same sign ? 270 rsbmi r0, r0, #0 271 mov pc, lr 272 27311: movlo r0, #0 274 moveq r0, ip, asr #31 275 orreq r0, r0, #1 276 mov pc, lr 277 27812: ARM_DIV2_ORDER r1, r2 279 280 cmp ip, #0 281 mov r0, r3, lsr r2 282 rsbmi r0, r0, #0 283 mov pc, lr 284 285 286ENTRY(__modsi3) 287 288 cmp r1, #0 289 beq Ldiv0 290 rsbmi r1, r1, #0 @ loops below use unsigned. 291 movs ip, r0 @ preserve sign of dividend 292 rsbmi r0, r0, #0 @ if negative make positive 293 subs r2, r1, #1 @ compare divisor with 1 294 cmpne r0, r1 @ compare dividend with divisor 295 moveq r0, #0 296 tsthi r1, r2 @ see if divisor is power of 2 297 andeq r0, r0, r2 298 bls 10f 299 300 ARM_MOD_BODY r0, r1, r2, r3 301 30210: cmp ip, #0 303 rsbmi r0, r0, #0 304 mov pc, lr 305 306 307Ldiv0: 308 309 str lr, [sp, #-4]! 310 bl __div0 311 mov r0, #0 @ About as wrong as it could be. 312 ldr pc, [sp], #4 313 314 315