标签：zed int min pow useful soft only org substr
/* * linux/arch/arm/lib/lib1funcs.S: Optimized ARM division routines * * Author: Nicolas Pitre <nico@cam.org> * - contributed to gcc-3.4 on Sep 30, 2003 * - adapted for the Linux kernel on Oct 2, 2003 */ /* Copyright 1995, 1996, 1998, 1999, 2000, 2003 Free Software Foundation, Inc. This file is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. In addition to the permissions in the GNU General Public License, the Free Software Foundation gives you unlimited permission to link the compiled version of this file into combinations with other programs, and to distribute those combinations without any restriction coming from the use of this file. (The General Public License restrictions do apply in other respects; for example, they cover modification of the file, and distribution when not linked into a combine executable.) This file is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; see the file COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ @ #include <linux/linkage.h> @ #include <asm/assembler.h> #define ALIGN .align 4,0x90 #define __LINUX_ARM_ARCH__ 1 #define CONFIG_AEABI #define ENTRY(name) .globl name; \ ALIGN; \ name: .macro ARM_DIV_BODY dividend, divisor, result, curbit #if __LINUX_ARM_ARCH__ >= 5 clz \curbit, \divisor clz \result, \dividend sub \result, \curbit, \result mov \curbit, #1 mov \divisor, \divisor, lsl \result mov \curbit, \curbit, lsl \result mov \result, #0 #else @ Initially shift the divisor left 3 bits if possible, @ set curbit accordingly. This allows for curbit to be located @ at the left end of each 4 bit nibbles in the division loop @ to save one loop in most cases. tst \divisor, #0xe0000000 moveq \divisor, \divisor, lsl #3 moveq \curbit, #8 movne \curbit, #1 @ Unless the divisor is very big, shift it up in multiples of @ four bits, since this is the amount of unwinding in the main @ division loop. Continue shifting until the divisor is @ larger than the dividend. 1: cmp \divisor, #0x10000000 cmplo \divisor, \dividend movlo \divisor, \divisor, lsl #4 movlo \curbit, \curbit, lsl #4 blo 1b @ For very big divisors, we must shift it a bit at a time, or @ we will be in danger of overflowing. 1: cmp \divisor, #0x80000000 cmplo \divisor, \dividend movlo \divisor, \divisor, lsl #1 movlo \curbit, \curbit, lsl #1 blo 1b mov \result, #0 #endif @ Division loop 1: cmp \dividend, \divisor subhs \dividend, \dividend, \divisor orrhs \result, \result, \curbit cmp \dividend, \divisor, lsr #1 subhs \dividend, \dividend, \divisor, lsr #1 orrhs \result, \result, \curbit, lsr #1 cmp \dividend, \divisor, lsr #2 subhs \dividend, \dividend, \divisor, lsr #2 orrhs \result, \result, \curbit, lsr #2 cmp \dividend, \divisor, lsr #3 subhs \dividend, \dividend, \divisor, lsr #3 orrhs \result, \result, \curbit, lsr #3 cmp \dividend, #0 @ Early termination? movnes \curbit, \curbit, lsr #4 @ No, any more bits to do? movne \divisor, \divisor, lsr #4 bne 1b .endm .macro ARM_DIV2_ORDER divisor, order #if __LINUX_ARM_ARCH__ >= 5 clz \order, \divisor rsb \order, \order, #31 #else cmp \divisor, #(1 << 16) movhs \divisor, \divisor, lsr #16 movhs \order, #16 movlo \order, #0 cmp \divisor, #(1 << 8) movhs \divisor, \divisor, lsr #8 addhs \order, \order, #8 cmp \divisor, #(1 << 4) movhs \divisor, \divisor, lsr #4 addhs \order, \order, #4 cmp \divisor, #(1 << 2) addhi \order, \order, #3 addls \order, \order, \divisor, lsr #1 #endif .endm .macro ARM_MOD_BODY dividend, divisor, order, spare #if __LINUX_ARM_ARCH__ >= 5 clz \order, \divisor clz \spare, \dividend sub \order, \order, \spare mov \divisor, \divisor, lsl \order #else mov \order, #0 @ Unless the divisor is very big, shift it up in multiples of @ four bits, since this is the amount of unwinding in the main @ division loop. Continue shifting until the divisor is @ larger than the dividend. 1: cmp \divisor, #0x10000000 cmplo \divisor, \dividend movlo \divisor, \divisor, lsl #4 addlo \order, \order, #4 blo 1b @ For very big divisors, we must shift it a bit at a time, or @ we will be in danger of overflowing. 1: cmp \divisor, #0x80000000 cmplo \divisor, \dividend movlo \divisor, \divisor, lsl #1 addlo \order, \order, #1 blo 1b #endif @ Perform all needed substractions to keep only the reminder. @ Do comparisons in batch of 4 first. subs \order, \order, #3 @ yes, 3 is intended here blt 2f 1: cmp \dividend, \divisor subhs \dividend, \dividend, \divisor cmp \dividend, \divisor, lsr #1 subhs \dividend, \dividend, \divisor, lsr #1 cmp \dividend, \divisor, lsr #2 subhs \dividend, \dividend, \divisor, lsr #2 cmp \dividend, \divisor, lsr #3 subhs \dividend, \dividend, \divisor, lsr #3 cmp \dividend, #1 mov \divisor, \divisor, lsr #4 subges \order, \order, #4 bge 1b tst \order, #3 teqne \dividend, #0 beq 5f @ Either 1, 2 or 3 comparison/substractions are left. 2: cmn \order, #2 blt 4f beq 3f cmp \dividend, \divisor subhs \dividend, \dividend, \divisor mov \divisor, \divisor, lsr #1 3: cmp \dividend, \divisor subhs \dividend, \dividend, \divisor mov \divisor, \divisor, lsr #1 4: cmp \dividend, \divisor subhs \dividend, \dividend, \divisor 5: .endm ENTRY(__udivsi3) ENTRY(__aeabi_uidiv) subs r2, r1, #1 moveq pc, lr bcc Ldiv0 cmp r0, r1 bls 11f tst r1, r2 beq 12f ARM_DIV_BODY r0, r1, r2, r3 mov r0, r2 mov pc, lr 11: moveq r0, #1 movne r0, #0 mov pc, lr 12: ARM_DIV2_ORDER r1, r2 mov r0, r0, lsr r2 mov pc, lr ENTRY(__umodsi3) subs r2, r1, #1 @ compare divisor with 1 bcc Ldiv0 cmpne r0, r1 @ compare dividend with divisor moveq r0, #0 tsthi r1, r2 @ see if divisor is power of 2 andeq r0, r0, r2 movls pc, lr ARM_MOD_BODY r0, r1, r2, r3 mov pc, lr ENTRY(__divsi3) ENTRY(__aeabi_idiv) cmp r1, #0 eor ip, r0, r1 @ save the sign of the result. beq Ldiv0 rsbmi r1, r1, #0 @ loops below use unsigned. subs r2, r1, #1 @ division by 1 or -1 ? beq 10f movs r3, r0 rsbmi r3, r0, #0 @ positive dividend value cmp r3, r1 bls 11f tst r1, r2 @ divisor is power of 2 ? beq 12f ARM_DIV_BODY r3, r1, r0, r2 cmp ip, #0 rsbmi r0, r0, #0 mov pc, lr 10: teq ip, r0 @ same sign ? rsbmi r0, r0, #0 mov pc, lr 11: movlo r0, #0 moveq r0, ip, asr #31 orreq r0, r0, #1 mov pc, lr 12: ARM_DIV2_ORDER r1, r2 cmp ip, #0 mov r0, r3, lsr r2 rsbmi r0, r0, #0 mov pc, lr ENTRY(__modsi3) cmp r1, #0 beq Ldiv0 rsbmi r1, r1, #0 @ loops below use unsigned. movs ip, r0 @ preserve sign of dividend rsbmi r0, r0, #0 @ if negative make positive subs r2, r1, #1 @ compare divisor with 1 cmpne r0, r1 @ compare dividend with divisor moveq r0, #0 tsthi r1, r2 @ see if divisor is power of 2 andeq r0, r0, r2 bls 10f ARM_MOD_BODY r0, r1, r2, r3 10: cmp ip, #0 rsbmi r0, r0, #0 mov pc, lr #ifdef CONFIG_AEABI ENTRY(__aeabi_uidivmod) stmfd sp!, {r0, r1, ip, lr} bl __aeabi_uidiv ldmfd sp!, {r1, r2, ip, lr} mul r3, r0, r2 sub r1, r1, r3 mov pc, lr ENTRY(__aeabi_idivmod) stmfd sp!, {r0, r1, ip, lr} bl __aeabi_idiv ldmfd sp!, {r1, r2, ip, lr} mul r3, r0, r2 sub r1, r1, r3 mov pc, lr #endif Ldiv0: str lr, [sp, #-8]! @ bl __div0 mov r0, #0 @ About as wrong as it could be. ldr pc, [sp], #8
标签：zed int min pow useful soft only org substr
原文地址：https://www.cnblogs.com/fox-Benjiaming/p/12340887.html
