Root/lib/div64.c

1/*
2 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
3 *
4 * Based on former do_div() implementation from asm-parisc/div64.h:
5 * Copyright (C) 1999 Hewlett-Packard Co
6 * Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
7 *
8 *
9 * Generic C version of 64bit/32bit division and modulo, with
10 * 64bit result and 32bit remainder.
11 *
12 * The fast case for (n>>32 == 0) is handled inline by do_div().
13 *
14 * Code generated for this function might be very inefficient
15 * for some CPUs. __div64_32() can be overridden by linking arch-specific
16 * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
17 */
18
19#include <linux/export.h>
20#include <linux/kernel.h>
21#include <linux/math64.h>
22
23/* Not needed on 64bit architectures */
24#if BITS_PER_LONG == 32
25
26uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
27{
28    uint64_t rem = *n;
29    uint64_t b = base;
30    uint64_t res, d = 1;
31    uint32_t high = rem >> 32;
32
33    /* Reduce the thing a bit first */
34    res = 0;
35    if (high >= base) {
36        high /= base;
37        res = (uint64_t) high << 32;
38        rem -= (uint64_t) (high*base) << 32;
39    }
40
41    while ((int64_t)b > 0 && b < rem) {
42        b = b+b;
43        d = d+d;
44    }
45
46    do {
47        if (rem >= b) {
48            rem -= b;
49            res += d;
50        }
51        b >>= 1;
52        d >>= 1;
53    } while (d);
54
55    *n = res;
56    return rem;
57}
58
59EXPORT_SYMBOL(__div64_32);
60
61#ifndef div_s64_rem
62s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
63{
64    u64 quotient;
65
66    if (dividend < 0) {
67        quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
68        *remainder = -*remainder;
69        if (divisor > 0)
70            quotient = -quotient;
71    } else {
72        quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
73        if (divisor < 0)
74            quotient = -quotient;
75    }
76    return quotient;
77}
78EXPORT_SYMBOL(div_s64_rem);
79#endif
80
81/**
82 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
83 * @dividend: 64bit dividend
84 * @divisor: 64bit divisor
85 * @remainder: 64bit remainder
86 *
87 * This implementation is a comparable to algorithm used by div64_u64.
88 * But this operation, which includes math for calculating the remainder,
89 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
90 * systems.
91 */
92#ifndef div64_u64_rem
93u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
94{
95    u32 high = divisor >> 32;
96    u64 quot;
97
98    if (high == 0) {
99        u32 rem32;
100        quot = div_u64_rem(dividend, divisor, &rem32);
101        *remainder = rem32;
102    } else {
103        int n = 1 + fls(high);
104        quot = div_u64(dividend >> n, divisor >> n);
105
106        if (quot != 0)
107            quot--;
108
109        *remainder = dividend - quot * divisor;
110        if (*remainder >= divisor) {
111            quot++;
112            *remainder -= divisor;
113        }
114    }
115
116    return quot;
117}
118EXPORT_SYMBOL(div64_u64_rem);
119#endif
120
121/**
122 * div64_u64 - unsigned 64bit divide with 64bit divisor
123 * @dividend: 64bit dividend
124 * @divisor: 64bit divisor
125 *
126 * This implementation is a modified version of the algorithm proposed
127 * by the book 'Hacker's Delight'. The original source and full proof
128 * can be found here and is available for use without restriction.
129 *
130 * 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c.txt'
131 */
132#ifndef div64_u64
133u64 div64_u64(u64 dividend, u64 divisor)
134{
135    u32 high = divisor >> 32;
136    u64 quot;
137
138    if (high == 0) {
139        quot = div_u64(dividend, divisor);
140    } else {
141        int n = 1 + fls(high);
142        quot = div_u64(dividend >> n, divisor >> n);
143
144        if (quot != 0)
145            quot--;
146        if ((dividend - quot * divisor) >= divisor)
147            quot++;
148    }
149
150    return quot;
151}
152EXPORT_SYMBOL(div64_u64);
153#endif
154
155/**
156 * div64_s64 - signed 64bit divide with 64bit divisor
157 * @dividend: 64bit dividend
158 * @divisor: 64bit divisor
159 */
160#ifndef div64_s64
161s64 div64_s64(s64 dividend, s64 divisor)
162{
163    s64 quot, t;
164
165    quot = div64_u64(abs64(dividend), abs64(divisor));
166    t = (dividend ^ divisor) >> 63;
167
168    return (quot ^ t) - t;
169}
170EXPORT_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 */
179u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
180{
181    return __iter_div_u64_rem(dividend, divisor, remainder);
182}
183EXPORT_SYMBOL(iter_div_u64_rem);
184

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