github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpn/arm/udiv.asm (about)

     1  dnl  ARM mpn_udiv_qrnnd -- divide a two limb dividend and a one limb divisor.
     2  dnl  Return quotient and store remainder through a supplied pointer.
     3  
     4  dnl  Copyright 2001, 2012 Free Software Foundation, Inc.
     5  
     6  dnl  This file is part of the GNU MP Library.
     7  dnl
     8  dnl  The GNU MP Library is free software; you can redistribute it and/or modify
     9  dnl  it under the terms of either:
    10  dnl
    11  dnl    * the GNU Lesser General Public License as published by the Free
    12  dnl      Software Foundation; either version 3 of the License, or (at your
    13  dnl      option) any later version.
    14  dnl
    15  dnl  or
    16  dnl
    17  dnl    * the GNU General Public License as published by the Free Software
    18  dnl      Foundation; either version 2 of the License, or (at your option) any
    19  dnl      later version.
    20  dnl
    21  dnl  or both in parallel, as here.
    22  dnl
    23  dnl  The GNU MP Library is distributed in the hope that it will be useful, but
    24  dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    25  dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    26  dnl  for more details.
    27  dnl
    28  dnl  You should have received copies of the GNU General Public License and the
    29  dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
    30  dnl  see https://www.gnu.org/licenses/.
    31  
    32  include(`../config.m4')
    33  
    34  C INPUT PARAMETERS
    35  define(`rem_ptr',`r0')
    36  define(`n1',`r1')
    37  define(`n0',`r2')
    38  define(`d',`r3')
    39  
    40  C divstep -- develop one quotient bit.  Dividend in $1$2, divisor in $3.
    41  C Quotient bit is shifted into $2.
    42  define(`divstep',
    43         `adcs	$2, $2, $2
    44  	adc	$1, $1, $1
    45  	cmp	$1, $3
    46  	subcs	$1, $1, $3')
    47  
    48  ASM_START()
    49  PROLOGUE(mpn_udiv_qrnnd)
    50  	mov	r12, #8			C loop counter for both loops below
    51  	cmp	d, #0x80000000		C check divisor msb and clear carry
    52  	bcs	L(_large_divisor)
    53  
    54  L(oop):	divstep(n1,n0,d)
    55  	divstep(n1,n0,d)
    56  	divstep(n1,n0,d)
    57  	divstep(n1,n0,d)
    58  	sub	r12, r12, #1
    59  	teq	r12, #0
    60  	bne	L(oop)
    61  
    62  	str	n1, [rem_ptr]		C store remainder
    63  	adc	r0, n0, n0		C quotient: add last carry from divstep
    64  	ret	lr
    65  
    66  L(_large_divisor):
    67  	stmfd	sp!, { r8, lr }
    68  
    69  	and	r8, n0, #1		C save lsb of dividend
    70  	mov	lr, n1, lsl #31
    71  	orrs	n0, lr, n0, lsr #1	C n0 = lo(n1n0 >> 1)
    72  	mov	n1, n1, lsr #1		C n1 = hi(n1n0 >> 1)
    73  
    74  	and	lr, d, #1		C save lsb of divisor
    75  	movs	d, d, lsr #1		C d = floor(orig_d / 2)
    76  	adc	d, d, #0		C d = ceil(orig_d / 2)
    77  
    78  L(oop2):
    79  	divstep(n1,n0,d)
    80  	divstep(n1,n0,d)
    81  	divstep(n1,n0,d)
    82  	divstep(n1,n0,d)
    83  	sub	r12, r12, #1
    84  	teq	r12, #0
    85  	bne	L(oop2)
    86  
    87  	adc	n0, n0, n0		C shift and add last carry from divstep
    88  	add	n1, r8, n1, lsl #1	C shift in omitted dividend lsb
    89  	tst	lr, lr			C test saved divisor lsb
    90  	beq	L(_even_divisor)
    91  
    92  	rsb	d, lr, d, lsl #1	C restore orig d value
    93  	adds	n1, n1, n0		C fix remainder for omitted divisor lsb
    94  	addcs	n0, n0, #1		C adjust quotient if rem. fix carried
    95  	subcs	n1, n1, d		C adjust remainder accordingly
    96  	cmp	n1, d			C remainder >= divisor?
    97  	subcs	n1, n1, d		C adjust remainder
    98  	addcs	n0, n0, #1		C adjust quotient
    99  
   100  L(_even_divisor):
   101  	str	n1, [rem_ptr]		C store remainder
   102  	mov	r0, n0			C quotient
   103  	ldmfd	sp!, { r8, pc }
   104  EPILOGUE(mpn_udiv_qrnnd)