projects/linux·blob master · refs

55 lines · 1.7 KiB

1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/*
3 * Divide a 64-bit unsigned number by a 32-bit unsigned number.
4 * This routine assumes that the top 32 bits of the dividend are
5 * non-zero to start with.
6 * On entry, r3 points to the dividend, which get overwritten with
7 * the 64-bit quotient, and r4 contains the divisor.
8 * On exit, r3 contains the remainder.
9 *
10 * Copyright (C) 2002 Paul Mackerras, IBM Corp.
11 */
12#include <asm/ppc_asm.h>
13#include <asm/processor.h>
14
15_GLOBAL(__div64_32)
16 lwz r5,0(r3) # get the dividend into r5/r6
17 lwz r6,4(r3)
18 cmplw r5,r4
19 li r7,0
20 li r8,0
21 blt 1f
22 divwu r7,r5,r4 # if dividend.hi >= divisor,
23 mullw r0,r7,r4 # quotient.hi = dividend.hi / divisor
24 subf. r5,r0,r5 # dividend.hi %= divisor
25 beq 3f
261: mr r11,r5 # here dividend.hi != 0
27 andis. r0,r5,0xc000
28 bne 2f
29 cntlzw r0,r5 # we are shifting the dividend right
30 li r10,-1 # to make it < 2^32, and shifting
31 srw r10,r10,r0 # the divisor right the same amount,
32 addc r9,r4,r10 # rounding up (so the estimate cannot
33 andc r11,r6,r10 # ever be too large, only too small)
34 andc r9,r9,r10
35 addze r9,r9
36 or r11,r5,r11
37 rotlw r9,r9,r0
38 rotlw r11,r11,r0
39 divwu r11,r11,r9 # then we divide the shifted quantities
402: mullw r10,r11,r4 # to get an estimate of the quotient,
41 mulhwu r9,r11,r4 # multiply the estimate by the divisor,
42 subfc r6,r10,r6 # take the product from the divisor,
43 add r8,r8,r11 # and add the estimate to the accumulated
44 subfe. r5,r9,r5 # quotient
45 bne 1b
463: cmplw r6,r4
47 blt 4f
48 divwu r0,r6,r4 # perform the remaining 32-bit division
49 mullw r10,r0,r4 # and get the remainder
50 add r8,r8,r0
51 subf r6,r10,r6
524: stw r7,0(r3) # return the quotient in *r3
53 stw r8,4(r3)
54 mr r3,r6 # return the remainder in r3
55 blr