1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
4 *
5 * Based on former do_div() implementation from asm-parisc/div64.h:
6 * Copyright (C) 1999 Hewlett-Packard Co
7 * Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
8 *
9 *
10 * Generic C version of 64bit/32bit division and modulo, with
11 * 64bit result and 32bit remainder.
12 *
13 * The fast case for (n>>32 == 0) is handled inline by do_div().
14 *
15 * Code generated for this function might be very inefficient
16 * for some CPUs. __div64_32() can be overridden by linking arch-specific
17 * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S
18 * or by defining a preprocessor macro in arch/include/asm/div64.h.
19 */
20
21 #include <linux/bitops.h>
22 #include <linux/export.h>
23 #include <linux/math.h>
24 #include <linux/math64.h>
25 #include <linux/log2.h>
26
27 /* Not needed on 64bit architectures */
28 #if BITS_PER_LONG == 32
29
30 #ifndef __div64_32
__div64_32(uint64_t * n,uint32_t base)31 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
32 {
33 uint64_t rem = *n;
34 uint64_t b = base;
35 uint64_t res, d = 1;
36 uint32_t high = rem >> 32;
37
38 /* Reduce the thing a bit first */
39 res = 0;
40 if (high >= base) {
41 high /= base;
42 res = (uint64_t) high << 32;
43 rem -= (uint64_t) (high*base) << 32;
44 }
45
46 while ((int64_t)b > 0 && b < rem) {
47 b = b+b;
48 d = d+d;
49 }
50
51 do {
52 if (rem >= b) {
53 rem -= b;
54 res += d;
55 }
56 b >>= 1;
57 d >>= 1;
58 } while (d);
59
60 *n = res;
61 return rem;
62 }
63 EXPORT_SYMBOL(__div64_32);
64 #endif
65
66 #ifndef div_s64_rem
div_s64_rem(s64 dividend,s32 divisor,s32 * remainder)67 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
68 {
69 u64 quotient;
70
71 if (dividend < 0) {
72 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
73 *remainder = -*remainder;
74 if (divisor > 0)
75 quotient = -quotient;
76 } else {
77 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
78 if (divisor < 0)
79 quotient = -quotient;
80 }
81 return quotient;
82 }
83 EXPORT_SYMBOL(div_s64_rem);
84 #endif
85
86 /*
87 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
88 * @dividend: 64bit dividend
89 * @divisor: 64bit divisor
90 * @remainder: 64bit remainder
91 *
92 * This implementation is a comparable to algorithm used by div64_u64.
93 * But this operation, which includes math for calculating the remainder,
94 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
95 * systems.
96 */
97 #ifndef div64_u64_rem
div64_u64_rem(u64 dividend,u64 divisor,u64 * remainder)98 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
99 {
100 u32 high = divisor >> 32;
101 u64 quot;
102
103 if (high == 0) {
104 u32 rem32;
105 quot = div_u64_rem(dividend, divisor, &rem32);
106 *remainder = rem32;
107 } else {
108 int n = fls(high);
109 quot = div_u64(dividend >> n, divisor >> n);
110
111 if (quot != 0)
112 quot--;
113
114 *remainder = dividend - quot * divisor;
115 if (*remainder >= divisor) {
116 quot++;
117 *remainder -= divisor;
118 }
119 }
120
121 return quot;
122 }
123 EXPORT_SYMBOL(div64_u64_rem);
124 #endif
125
126 /*
127 * div64_u64 - unsigned 64bit divide with 64bit divisor
128 * @dividend: 64bit dividend
129 * @divisor: 64bit divisor
130 *
131 * This implementation is a modified version of the algorithm proposed
132 * by the book 'Hacker's Delight'. The original source and full proof
133 * can be found here and is available for use without restriction.
134 *
135 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
136 */
137 #ifndef div64_u64
div64_u64(u64 dividend,u64 divisor)138 u64 div64_u64(u64 dividend, u64 divisor)
139 {
140 u32 high = divisor >> 32;
141 u64 quot;
142
143 if (high == 0) {
144 quot = div_u64(dividend, divisor);
145 } else {
146 int n = fls(high);
147 quot = div_u64(dividend >> n, divisor >> n);
148
149 if (quot != 0)
150 quot--;
151 if ((dividend - quot * divisor) >= divisor)
152 quot++;
153 }
154
155 return quot;
156 }
157 EXPORT_SYMBOL(div64_u64);
158 #endif
159
160 #ifndef div64_s64
div64_s64(s64 dividend,s64 divisor)161 s64 div64_s64(s64 dividend, s64 divisor)
162 {
163 s64 quot, t;
164
165 quot = div64_u64(abs(dividend), abs(divisor));
166 t = (dividend ^ divisor) >> 63;
167
168 return (quot ^ t) - t;
169 }
170 EXPORT_SYMBOL(div64_s64);
171 #endif
172
173 #endif /* BITS_PER_LONG == 32 */
174
175 /*
176 * Iterative div/mod for use when dividend is not expected to be much
177 * bigger than divisor.
178 */
iter_div_u64_rem(u64 dividend,u32 divisor,u64 * remainder)179 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
180 {
181 return __iter_div_u64_rem(dividend, divisor, remainder);
182 }
183 EXPORT_SYMBOL(iter_div_u64_rem);
184
185 #ifndef mul_u64_u64_div_u64
mul_u64_u64_div_u64(u64 a,u64 b,u64 c)186 u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
187 {
188 u64 res = 0, div, rem;
189 int shift;
190
191 /* can a * b overflow ? */
192 if (ilog2(a) + ilog2(b) > 62) {
193 /*
194 * (b * a) / c is equal to
195 *
196 * (b / c) * a +
197 * (b % c) * a / c
198 *
199 * if nothing overflows. Can the 1st multiplication
200 * overflow? Yes, but we do not care: this can only
201 * happen if the end result can't fit in u64 anyway.
202 *
203 * So the code below does
204 *
205 * res = (b / c) * a;
206 * b = b % c;
207 */
208 div = div64_u64_rem(b, c, &rem);
209 res = div * a;
210 b = rem;
211
212 shift = ilog2(a) + ilog2(b) - 62;
213 if (shift > 0) {
214 /* drop precision */
215 b >>= shift;
216 c >>= shift;
217 if (!c)
218 return res;
219 }
220 }
221
222 return res + div64_u64(a * b, c);
223 }
224 EXPORT_SYMBOL(mul_u64_u64_div_u64);
225 #endif
226