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dnl ARM mpn_udiv_qrnnd -- divide a two limb dividend and a one limb divisor.
dnl Return quotient and store remainder through a supplied pointer.
dnl Copyright 2001, 2012 Free Software Foundation, Inc.
dnl This file is part of the GNU MP Library.
dnl
dnl The GNU MP Library is free software; you can redistribute it and/or modify
dnl it under the terms of either:
dnl
dnl * the GNU Lesser General Public License as published by the Free
dnl Software Foundation; either version 3 of the License, or (at your
dnl option) any later version.
dnl
dnl or
dnl
dnl * the GNU General Public License as published by the Free Software
dnl Foundation; either version 2 of the License, or (at your option) any
dnl later version.
dnl
dnl or both in parallel, as here.
dnl
dnl The GNU MP Library is distributed in the hope that it will be useful, but
dnl WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
dnl or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
dnl for more details.
dnl
dnl You should have received copies of the GNU General Public License and the
dnl GNU Lesser General Public License along with the GNU MP Library. If not,
dnl see https://www.gnu.org/licenses/.
include(`../config.m4')
C INPUT PARAMETERS
define(`rem_ptr',`r0')
define(`n1',`r1')
define(`n0',`r2')
define(`d',`r3')
C divstep -- develop one quotient bit. Dividend in $1$2, divisor in $3.
C Quotient bit is shifted into $2.
define(`divstep',
`adcs $2, $2, $2
adc $1, $1, $1
cmp $1, $3
subcs $1, $1, $3')
ASM_START()
PROLOGUE(mpn_udiv_qrnnd)
mov r12, #8 C loop counter for both loops below
cmp d, #0x80000000 C check divisor msb and clear carry
bcs L(_large_divisor)
L(oop): divstep(n1,n0,d)
divstep(n1,n0,d)
divstep(n1,n0,d)
divstep(n1,n0,d)
sub r12, r12, #1
teq r12, #0
bne L(oop)
str n1, [rem_ptr] C store remainder
adc r0, n0, n0 C quotient: add last carry from divstep
return lr
L(_large_divisor):
stmfd sp!, { r8, lr }
and r8, n0, #1 C save lsb of dividend
mov lr, n1, lsl #31
orrs n0, lr, n0, lsr #1 C n0 = lo(n1n0 >> 1)
mov n1, n1, lsr #1 C n1 = hi(n1n0 >> 1)
and lr, d, #1 C save lsb of divisor
movs d, d, lsr #1 C d = floor(orig_d / 2)
adc d, d, #0 C d = ceil(orig_d / 2)
L(oop2):
divstep(n1,n0,d)
divstep(n1,n0,d)
divstep(n1,n0,d)
divstep(n1,n0,d)
sub r12, r12, #1
teq r12, #0
bne L(oop2)
adc n0, n0, n0 C shift and add last carry from divstep
add n1, r8, n1, lsl #1 C shift in omitted dividend lsb
tst lr, lr C test saved divisor lsb
beq L(_even_divisor)
rsb d, lr, d, lsl #1 C restore orig d value
adds n1, n1, n0 C fix remainder for omitted divisor lsb
addcs n0, n0, #1 C adjust quotient if rem. fix carried
subcs n1, n1, d C adjust remainder accordingly
cmp n1, d C remainder >= divisor?
subcs n1, n1, d C adjust remainder
addcs n0, n0, #1 C adjust quotient
L(_even_divisor):
str n1, [rem_ptr] C store remainder
mov r0, n0 C quotient
ldmfd sp!, { r8, pc }
EPILOGUE(mpn_udiv_qrnnd)
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