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Tom Rini83d290c2018-05-06 17:58:06 -04001/* SPDX-License-Identifier: GPL-2.0 */
Marek Vasut7b9f9c52016-05-26 18:01:42 +02002/*
3 * linux/arch/arm/lib/div64.S
4 *
5 * Optimized computation of 64-bit dividend / 32-bit divisor
6 *
7 * Author: Nicolas Pitre
8 * Created: Oct 5, 2003
9 * Copyright: Monta Vista Software, Inc.
Marek Vasut7b9f9c52016-05-26 18:01:42 +020010 */
11
12#include <linux/linkage.h>
13#include <asm/assembler.h>
14#ifdef __UBOOT__
15#define UNWIND(x...)
16#endif
17
18#ifdef __ARMEB__
19#define xh r0
20#define xl r1
21#define yh r2
22#define yl r3
23#else
24#define xl r0
25#define xh r1
26#define yl r2
27#define yh r3
28#endif
29
30/*
31 * __do_div64: perform a division with 64-bit dividend and 32-bit divisor.
32 *
33 * Note: Calling convention is totally non standard for optimal code.
34 * This is meant to be used by do_div() from include/asm/div64.h only.
35 *
36 * Input parameters:
Wolfgang Denk0cf207e2021-09-27 17:42:39 +020037 * xh-xl = dividend (clobbered)
38 * r4 = divisor (preserved)
Marek Vasut7b9f9c52016-05-26 18:01:42 +020039 *
40 * Output values:
Wolfgang Denk0cf207e2021-09-27 17:42:39 +020041 * yh-yl = result
42 * xh = remainder
Marek Vasut7b9f9c52016-05-26 18:01:42 +020043 *
44 * Clobbered regs: xl, ip
45 */
46
Stephen Warrenb2f18582016-06-03 13:05:11 -060047.pushsection .text.__do_div64, "ax"
Marek Vasut7b9f9c52016-05-26 18:01:42 +020048ENTRY(__do_div64)
49UNWIND(.fnstart)
50
51 @ Test for easy paths first.
52 subs ip, r4, #1
53 bls 9f @ divisor is 0 or 1
54 tst ip, r4
55 beq 8f @ divisor is power of 2
56
57 @ See if we need to handle upper 32-bit result.
58 cmp xh, r4
59 mov yh, #0
60 blo 3f
61
62 @ Align divisor with upper part of dividend.
63 @ The aligned divisor is stored in yl preserving the original.
64 @ The bit position is stored in ip.
65
66#if __LINUX_ARM_ARCH__ >= 5
67
68 clz yl, r4
69 clz ip, xh
70 sub yl, yl, ip
71 mov ip, #1
72 mov ip, ip, lsl yl
73 mov yl, r4, lsl yl
74
75#else
76
77 mov yl, r4
78 mov ip, #1
791: cmp yl, #0x80000000
80 cmpcc yl, xh
81 movcc yl, yl, lsl #1
82 movcc ip, ip, lsl #1
83 bcc 1b
84
85#endif
86
87 @ The division loop for needed upper bit positions.
Wolfgang Denk0cf207e2021-09-27 17:42:39 +020088 @ Break out early if dividend reaches 0.
Marek Vasut7b9f9c52016-05-26 18:01:42 +0200892: cmp xh, yl
90 orrcs yh, yh, ip
Marek Vasut40d67c72016-05-26 18:01:43 +020091 subscs xh, xh, yl
92 movsne ip, ip, lsr #1
Marek Vasut7b9f9c52016-05-26 18:01:42 +020093 mov yl, yl, lsr #1
94 bne 2b
95
96 @ See if we need to handle lower 32-bit result.
973: cmp xh, #0
98 mov yl, #0
99 cmpeq xl, r4
100 movlo xh, xl
101 retlo lr
102
103 @ The division loop for lower bit positions.
104 @ Here we shift remainer bits leftwards rather than moving the
105 @ divisor for comparisons, considering the carry-out bit as well.
106 mov ip, #0x80000000
1074: movs xl, xl, lsl #1
108 adcs xh, xh, xh
109 beq 6f
110 cmpcc xh, r4
1115: orrcs yl, yl, ip
112 subcs xh, xh, r4
113 movs ip, ip, lsr #1
114 bne 4b
115 ret lr
116
117 @ The top part of remainder became zero. If carry is set
118 @ (the 33th bit) this is a false positive so resume the loop.
119 @ Otherwise, if lower part is also null then we are done.
1206: bcs 5b
121 cmp xl, #0
122 reteq lr
123
124 @ We still have remainer bits in the low part. Bring them up.
125
126#if __LINUX_ARM_ARCH__ >= 5
127
128 clz xh, xl @ we know xh is zero here so...
129 add xh, xh, #1
130 mov xl, xl, lsl xh
131 mov ip, ip, lsr xh
132
133#else
134
1357: movs xl, xl, lsl #1
136 mov ip, ip, lsr #1
137 bcc 7b
138
139#endif
140
141 @ Current remainder is now 1. It is worthless to compare with
142 @ divisor at this point since divisor can not be smaller than 3 here.
143 @ If possible, branch for another shift in the division loop.
144 @ If no bit position left then we are done.
145 movs ip, ip, lsr #1
146 mov xh, #1
147 bne 4b
148 ret lr
149
1508: @ Division by a power of 2: determine what that divisor order is
151 @ then simply shift values around
152
153#if __LINUX_ARM_ARCH__ >= 5
154
155 clz ip, r4
156 rsb ip, ip, #31
157
158#else
159
160 mov yl, r4
161 cmp r4, #(1 << 16)
162 mov ip, #0
163 movhs yl, yl, lsr #16
164 movhs ip, #16
165
166 cmp yl, #(1 << 8)
167 movhs yl, yl, lsr #8
168 addhs ip, ip, #8
169
170 cmp yl, #(1 << 4)
171 movhs yl, yl, lsr #4
172 addhs ip, ip, #4
173
174 cmp yl, #(1 << 2)
175 addhi ip, ip, #3
176 addls ip, ip, yl, lsr #1
177
178#endif
179
180 mov yh, xh, lsr ip
181 mov yl, xl, lsr ip
182 rsb ip, ip, #32
183 ARM( orr yl, yl, xh, lsl ip )
184 THUMB( lsl xh, xh, ip )
185 THUMB( orr yl, yl, xh )
186 mov xh, xl, lsl ip
187 mov xh, xh, lsr ip
188 ret lr
189
190 @ eq -> division by 1: obvious enough...
1919: moveq yl, xl
192 moveq yh, xh
193 moveq xh, #0
194 reteq lr
Marek Vasut7b9f9c52016-05-26 18:01:42 +0200195UNWIND(.fnend)
196
197UNWIND(.fnstart)
198UNWIND(.pad #4)
199UNWIND(.save {lr})
200Ldiv0_64:
201 @ Division by 0:
202 str lr, [sp, #-8]!
203 bl __div0
204
205 @ as wrong as it could be...
206 mov yl, #0
207 mov yh, #0
208 mov xh, #0
209 ldr pc, [sp], #8
210
211UNWIND(.fnend)
212ENDPROC(__do_div64)
Stephen Warrenb2f18582016-06-03 13:05:11 -0600213.popsection