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 : /**
67 : * div_s64_rem - signed 64bit divide with 64bit divisor and remainder
68 : * @dividend: 64bit dividend
69 : * @divisor: 64bit divisor
70 : * @remainder: 64bit remainder
71 : */
72 : #ifndef div_s64_rem
73 : s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
74 : {
75 : u64 quotient;
76 :
77 : if (dividend < 0) {
78 : quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
79 : *remainder = -*remainder;
80 : if (divisor > 0)
81 : quotient = -quotient;
82 : } else {
83 : quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
84 : if (divisor < 0)
85 : quotient = -quotient;
86 : }
87 : return quotient;
88 : }
89 : EXPORT_SYMBOL(div_s64_rem);
90 : #endif
91 :
92 : /**
93 : * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
94 : * @dividend: 64bit dividend
95 : * @divisor: 64bit divisor
96 : * @remainder: 64bit remainder
97 : *
98 : * This implementation is a comparable to algorithm used by div64_u64.
99 : * But this operation, which includes math for calculating the remainder,
100 : * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
101 : * systems.
102 : */
103 : #ifndef div64_u64_rem
104 : u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
105 : {
106 : u32 high = divisor >> 32;
107 : u64 quot;
108 :
109 : if (high == 0) {
110 : u32 rem32;
111 : quot = div_u64_rem(dividend, divisor, &rem32);
112 : *remainder = rem32;
113 : } else {
114 : int n = fls(high);
115 : quot = div_u64(dividend >> n, divisor >> n);
116 :
117 : if (quot != 0)
118 : quot--;
119 :
120 : *remainder = dividend - quot * divisor;
121 : if (*remainder >= divisor) {
122 : quot++;
123 : *remainder -= divisor;
124 : }
125 : }
126 :
127 : return quot;
128 : }
129 : EXPORT_SYMBOL(div64_u64_rem);
130 : #endif
131 :
132 : /**
133 : * div64_u64 - unsigned 64bit divide with 64bit divisor
134 : * @dividend: 64bit dividend
135 : * @divisor: 64bit divisor
136 : *
137 : * This implementation is a modified version of the algorithm proposed
138 : * by the book 'Hacker's Delight'. The original source and full proof
139 : * can be found here and is available for use without restriction.
140 : *
141 : * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
142 : */
143 : #ifndef div64_u64
144 : u64 div64_u64(u64 dividend, u64 divisor)
145 : {
146 : u32 high = divisor >> 32;
147 : u64 quot;
148 :
149 : if (high == 0) {
150 : quot = div_u64(dividend, divisor);
151 : } else {
152 : int n = fls(high);
153 : quot = div_u64(dividend >> n, divisor >> n);
154 :
155 : if (quot != 0)
156 : quot--;
157 : if ((dividend - quot * divisor) >= divisor)
158 : quot++;
159 : }
160 :
161 : return quot;
162 : }
163 : EXPORT_SYMBOL(div64_u64);
164 : #endif
165 :
166 : /**
167 : * div64_s64 - signed 64bit divide with 64bit divisor
168 : * @dividend: 64bit dividend
169 : * @divisor: 64bit divisor
170 : */
171 : #ifndef div64_s64
172 : s64 div64_s64(s64 dividend, s64 divisor)
173 : {
174 : s64 quot, t;
175 :
176 : quot = div64_u64(abs(dividend), abs(divisor));
177 : t = (dividend ^ divisor) >> 63;
178 :
179 : return (quot ^ t) - t;
180 : }
181 : EXPORT_SYMBOL(div64_s64);
182 : #endif
183 :
184 : #endif /* BITS_PER_LONG == 32 */
185 :
186 : /*
187 : * Iterative div/mod for use when dividend is not expected to be much
188 : * bigger than divisor.
189 : */
190 0 : u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
191 : {
192 0 : return __iter_div_u64_rem(dividend, divisor, remainder);
193 : }
194 : EXPORT_SYMBOL(iter_div_u64_rem);
195 :
196 : #ifndef mul_u64_u64_div_u64
197 : u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
198 : {
199 : u64 res = 0, div, rem;
200 : int shift;
201 :
202 : /* can a * b overflow ? */
203 : if (ilog2(a) + ilog2(b) > 62) {
204 : /*
205 : * (b * a) / c is equal to
206 : *
207 : * (b / c) * a +
208 : * (b % c) * a / c
209 : *
210 : * if nothing overflows. Can the 1st multiplication
211 : * overflow? Yes, but we do not care: this can only
212 : * happen if the end result can't fit in u64 anyway.
213 : *
214 : * So the code below does
215 : *
216 : * res = (b / c) * a;
217 : * b = b % c;
218 : */
219 : div = div64_u64_rem(b, c, &rem);
220 : res = div * a;
221 : b = rem;
222 :
223 : shift = ilog2(a) + ilog2(b) - 62;
224 : if (shift > 0) {
225 : /* drop precision */
226 : b >>= shift;
227 : c >>= shift;
228 : if (!c)
229 : return res;
230 : }
231 : }
232 :
233 : return res + div64_u64(a * b, c);
234 : }
235 : #endif
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