linux/arch/powerpc/boot/div64.S

/*
 * Divide a 64-bit unsigned number by a 32-bit unsigned number.
 * This routine assumes that the top 32 bits of the dividend are
 * non-zero to start with.
 * On entry, r3 points to the dividend, which get overwritten with
 * the 64-bit quotient, and r4 contains the divisor.
 * On exit, r3 contains the remainder.
 *
 * Copyright (C) 2002 Paul Mackerras, IBM Corp.
 *
 * This program 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 of the License, or (at your option) any later version.
 */
#include "ppc_asm.h"

	.globl __div64_32
__div64_32:
	lwz	r5,0(r3)	# get the dividend into r5/r6
	lwz	r6,4(r3)
	cmplw	r5,r4
	li	r7,0
	li	r8,0
	blt	1f
	divwu	r7,r5,r4	# if dividend.hi >= divisor,
	mullw	r0,r7,r4	# quotient.hi = dividend.hi / divisor
	subf.	r5,r0,r5	# dividend.hi %= divisor
	beq	3f
1:	mr	r11,r5		# here dividend.hi != 0
	andis.	r0,r5,0xc000
	bne	2f
	cntlzw	r0,r5		# we are shifting the dividend right
	li	r10,-1		# to make it < 2^32, and shifting
	srw	r10,r10,r0	# the divisor right the same amount,
	add	r9,r4,r10	# rounding up (so the estimate cannot
	andc	r11,r6,r10	# ever be too large, only too small)
	andc	r9,r9,r10
	or	r11,r5,r11
	rotlw	r9,r9,r0
	rotlw	r11,r11,r0
	divwu	r11,r11,r9	# then we divide the shifted quantities
2:	mullw	r10,r11,r4	# to get an estimate of the quotient,
	mulhwu	r9,r11,r4	# multiply the estimate by the divisor,
	subfc	r6,r10,r6	# take the product from the divisor,
	add	r8,r8,r11	# and add the estimate to the accumulated
	subfe.	r5,r9,r5	# quotient
	bne	1b
3:	cmplw	r6,r4
	blt	4f
	divwu	r0,r6,r4	# perform the remaining 32-bit division
	mullw	r10,r0,r4	# and get the remainder
	add	r8,r8,r0
	subf	r6,r10,r6
4:	stw	r7,0(r3)	# return the quotient in *r3
	stw	r8,4(r3)
	mr	r3,r6		# return the remainder in r3
	blr