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/* Runtime ABI for the ARM Cortex-M
* uldivmod.S: unsigned 64 bit division
*
* Copyright (c) 2012 Jörg Mische <bobbl@gmx.de>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "software_panic.h"
.syntax unified
.text
.code 16
@ {unsigned long long quotient, unsigned long long remainder}
@ __aeabi_uldivmod(unsigned long long numerator, unsigned long long denominator)
@
@ Divide r1:r0 by r3:r2 and return the quotient in r1:r0 and the remainder
@ in r3:r2 (all unsigned)
@
.thumb_func
.section .text.__aeabi_uldivmod
.global __aeabi_uldivmod
__aeabi_uldivmod:
cmp r3, #0
bne L_large_denom
cmp r2, #0
beq L_divison_by_0
cmp r1, #0
beq L_fallback_32bits
@ case 1: num >= 2^32 and denom < 2^32
@ Result might be > 2^32, therefore we first calculate the upper 32
@ bits of the result. It is done similar to the calculation of the
@ lower 32 bits, but with a denominator that is shifted by 32.
@ Hence the lower 32 bits of the denominator are always 0 and the
@ costly 64 bit shift and sub operations can be replaced by cheap 32
@ bit operations.
push {r4, r5, r6, r7, lr}
@ shift left the denominator until it is greater than the numerator
@ denom(r7:r6) = r3:r2 << 32
@ TODO(crosbug.com/p/36128): Loops like this (which occur in several
@ places in this file) are inefficent in ARMv6-m.
movs r5, #1 @ bitmask
adds r7, r2, #0 @ dont shift if denominator would overflow
bmi L_upper_result
cmp r1, r7
blo L_upper_result
L_denom_shift_loop1:
lsl r5, #1
lsls r7, #1
bmi L_upper_result @ dont shift if overflow
cmp r1, r7
bhs L_denom_shift_loop1
L_upper_result:
mov r3, r1
mov r2, r0
mov r1, #0 @ upper result = 0
mov r6, #0
L_sub_loop1:
orr r1, r5 @ result(r7:r6) |= bitmask(r5)
subs r2, r6 @ num -= denom
sbcs r3, r7
bhs L_done_sub1
eor r1, r5 @ undo add mask
adds r2, r6 @ undo subtract
adc r3, r3, r7
L_done_sub1:
lsrs r7, #1 @ denom(r7:r6) >>= 1
rrx r6, r6
lsrs r5, #1 @ bitmask(r5) >>= 1
bne L_sub_loop1
rrx r5, r5
b L_lower_result
@ case 2: division by 0
@ call __aeabi_ldiv0
L_divison_by_0:
b __aeabi_ldiv0
@ case 3: num < 2^32 and denom < 2^32
@ fallback to 32 bit division
L_fallback_32bits:
mov r1, r0
udiv r0, r0, r2 @ r0 = quotient
mul r3, r0, r2 @ r3 = quotient * divisor
sub r2, r1, r3 @ r2 = remainder
mov r1, #0
mov r3, #0
bx lr
@ case 4: denom >= 2^32
@ result is smaller than 2^32
L_large_denom:
push {r4, r5, r6, r7, lr}
mov r7, r3
mov r6, r2
mov r3, r1
mov r2, r0
@ Shift left the denominator until it is greater than the numerator
mov r1, #0 @ high word of result is 0
mov r5, #1 @ bitmask
adds r7, #0 @ dont shift if denominator would overflow
bmi L_lower_result
cmp r3, r7
blo L_lower_result
L_denom_shift_loop4:
lsl r5, #1
lsls r6, #1 @ denom(r7:r6) <<= 1
adcs r7, r7
bmi L_lower_result @ dont shift if overflow
cmp r3, r7
bhs L_denom_shift_loop4
L_lower_result:
movs r0, #0
L_sub_loop4:
orr r0, r5 @ result(r1:r0) |= bitmask(r5)
subs r2, r6 @ numerator -= denom
sbcs r3, r7
bhs L_done_sub4
eor r0, r5 @ undo add mask
adds r2, r6 @ undo subtract
adc r3, r3, r7
L_done_sub4:
lsrs r7, #1 @ denom(r7:r6) >>= 1
rrx r6, r6
lsrs r5, #1 @ bitmask(r5) >>= 1
bne L_sub_loop4
pop {r4, r5, r6, r7, pc}
__aeabi_ldiv0:
ldr SOFTWARE_PANIC_REASON_REG, =PANIC_SW_DIV_ZERO
mov SOFTWARE_PANIC_INFO_REG, r14
bl exception_panic
|
