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Diffstat (limited to 'arch/arm/lib/div64.S')
| -rw-r--r-- | arch/arm/lib/div64.S | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/arch/arm/lib/div64.S b/arch/arm/lib/div64.S new file mode 100644 index 0000000..ec9a1cd --- /dev/null +++ b/arch/arm/lib/div64.S @@ -0,0 +1,200 @@ +/* + * linux/arch/arm/lib/div64.S + * + * Optimized computation of 64-bit dividend / 32-bit divisor + * + * Author: Nicolas Pitre + * Created: Oct 5, 2003 + * Copyright: Monta Vista Software, Inc. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#include <linux/linkage.h> + +#ifdef __ARMEB__ +#define xh r0 +#define xl r1 +#define yh r2 +#define yl r3 +#else +#define xl r0 +#define xh r1 +#define yl r2 +#define yh r3 +#endif + +/* + * __do_div64: perform a division with 64-bit dividend and 32-bit divisor. + * + * Note: Calling convention is totally non standard for optimal code. + * This is meant to be used by do_div() from include/asm/div64.h only. + * + * Input parameters: + * xh-xl = dividend (clobbered) + * r4 = divisor (preserved) + * + * Output values: + * yh-yl = result + * xh = remainder + * + * Clobbered regs: xl, ip + */ + +ENTRY(__do_div64) + + @ Test for easy paths first. + subs ip, r4, #1 + bls 9f @ divisor is 0 or 1 + tst ip, r4 + beq 8f @ divisor is power of 2 + + @ See if we need to handle upper 32-bit result. + cmp xh, r4 + mov yh, #0 + blo 3f + + @ Align divisor with upper part of dividend. + @ The aligned divisor is stored in yl preserving the original. + @ The bit position is stored in ip. + +#if __LINUX_ARM_ARCH__ >= 5 + + clz yl, r4 + clz ip, xh + sub yl, yl, ip + mov ip, #1 + mov ip, ip, lsl yl + mov yl, r4, lsl yl + +#else + + mov yl, r4 + mov ip, #1 +1: cmp yl, #0x80000000 + cmpcc yl, xh + movcc yl, yl, lsl #1 + movcc ip, ip, lsl #1 + bcc 1b + +#endif + + @ The division loop for needed upper bit positions. + @ Break out early if dividend reaches 0. +2: cmp xh, yl + orrcs yh, yh, ip + subcss xh, xh, yl + movnes ip, ip, lsr #1 + mov yl, yl, lsr #1 + bne 2b + + @ See if we need to handle lower 32-bit result. +3: cmp xh, #0 + mov yl, #0 + cmpeq xl, r4 + movlo xh, xl + movlo pc, lr + + @ The division loop for lower bit positions. + @ Here we shift remainer bits leftwards rather than moving the + @ divisor for comparisons, considering the carry-out bit as well. + mov ip, #0x80000000 +4: movs xl, xl, lsl #1 + adcs xh, xh, xh + beq 6f + cmpcc xh, r4 +5: orrcs yl, yl, ip + subcs xh, xh, r4 + movs ip, ip, lsr #1 + bne 4b + mov pc, lr + + @ The top part of remainder became zero. If carry is set + @ (the 33th bit) this is a false positive so resume the loop. + @ Otherwise, if lower part is also null then we are done. +6: bcs 5b + cmp xl, #0 + moveq pc, lr + + @ We still have remainer bits in the low part. Bring them up. + +#if __LINUX_ARM_ARCH__ >= 5 + + clz xh, xl @ we know xh is zero here so... + add xh, xh, #1 + mov xl, xl, lsl xh + mov ip, ip, lsr xh + +#else + +7: movs xl, xl, lsl #1 + mov ip, ip, lsr #1 + bcc 7b + +#endif + + @ Current remainder is now 1. It is worthless to compare with + @ divisor at this point since divisor can not be smaller than 3 here. + @ If possible, branch for another shift in the division loop. + @ If no bit position left then we are done. + movs ip, ip, lsr #1 + mov xh, #1 + bne 4b + mov pc, lr + +8: @ Division by a power of 2: determine what that divisor order is + @ then simply shift values around + +#if __LINUX_ARM_ARCH__ >= 5 + + clz ip, r4 + rsb ip, ip, #31 + +#else + + mov yl, r4 + cmp r4, #(1 << 16) + mov ip, #0 + movhs yl, yl, lsr #16 + movhs ip, #16 + + cmp yl, #(1 << 8) + movhs yl, yl, lsr #8 + addhs ip, ip, #8 + + cmp yl, #(1 << 4) + movhs yl, yl, lsr #4 + addhs ip, ip, #4 + + cmp yl, #(1 << 2) + addhi ip, ip, #3 + addls ip, ip, yl, lsr #1 + +#endif + + mov yh, xh, lsr ip + mov yl, xl, lsr ip + rsb ip, ip, #32 + orr yl, yl, xh, lsl ip + mov xh, xl, lsl ip + mov xh, xh, lsr ip + mov pc, lr + + @ eq -> division by 1: obvious enough... +9: moveq yl, xl + moveq yh, xh + moveq xh, #0 + moveq pc, lr + + @ Division by 0: + str lr, [sp, #-4]! + bl __div0 + + @ as wrong as it could be... + mov yl, #0 + mov yh, #0 + mov xh, #0 + ldr pc, [sp], #4 + |
