Line data Source code
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
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
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
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
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
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 : */
179 0 : u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
180 : {
181 0 : return __iter_div_u64_rem(dividend, divisor, remainder);
182 : }
183 : EXPORT_SYMBOL(iter_div_u64_rem);
184 :
185 : #ifndef mul_u64_u64_div_u64
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
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