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Linux/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  * or by defining a preprocessor macro in arch/include/asm/div64.h.
 18  */
 19 
 20 #include <linux/export.h>
 21 #include <linux/kernel.h>
 22 #include <linux/math64.h>
 23 
 24 /* Not needed on 64bit architectures */
 25 #if BITS_PER_LONG == 32
 26 
 27 #ifndef __div64_32
 28 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
 29 {
 30         uint64_t rem = *n;
 31         uint64_t b = base;
 32         uint64_t res, d = 1;
 33         uint32_t high = rem >> 32;
 34 
 35         /* Reduce the thing a bit first */
 36         res = 0;
 37         if (high >= base) {
 38                 high /= base;
 39                 res = (uint64_t) high << 32;
 40                 rem -= (uint64_t) (high*base) << 32;
 41         }
 42 
 43         while ((int64_t)b > 0 && b < rem) {
 44                 b = b+b;
 45                 d = d+d;
 46         }
 47 
 48         do {
 49                 if (rem >= b) {
 50                         rem -= b;
 51                         res += d;
 52                 }
 53                 b >>= 1;
 54                 d >>= 1;
 55         } while (d);
 56 
 57         *n = res;
 58         return rem;
 59 }
 60 EXPORT_SYMBOL(__div64_32);
 61 #endif
 62 
 63 #ifndef div_s64_rem
 64 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
 65 {
 66         u64 quotient;
 67 
 68         if (dividend < 0) {
 69                 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
 70                 *remainder = -*remainder;
 71                 if (divisor > 0)
 72                         quotient = -quotient;
 73         } else {
 74                 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
 75                 if (divisor < 0)
 76                         quotient = -quotient;
 77         }
 78         return quotient;
 79 }
 80 EXPORT_SYMBOL(div_s64_rem);
 81 #endif
 82 
 83 /**
 84  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
 85  * @dividend:   64bit dividend
 86  * @divisor:    64bit divisor
 87  * @remainder:  64bit remainder
 88  *
 89  * This implementation is a comparable to algorithm used by div64_u64.
 90  * But this operation, which includes math for calculating the remainder,
 91  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
 92  * systems.
 93  */
 94 #ifndef div64_u64_rem
 95 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
 96 {
 97         u32 high = divisor >> 32;
 98         u64 quot;
 99 
100         if (high == 0) {
101                 u32 rem32;
102                 quot = div_u64_rem(dividend, divisor, &rem32);
103                 *remainder = rem32;
104         } else {
105                 int n = 1 + fls(high);
106                 quot = div_u64(dividend >> n, divisor >> n);
107 
108                 if (quot != 0)
109                         quot--;
110 
111                 *remainder = dividend - quot * divisor;
112                 if (*remainder >= divisor) {
113                         quot++;
114                         *remainder -= divisor;
115                 }
116         }
117 
118         return quot;
119 }
120 EXPORT_SYMBOL(div64_u64_rem);
121 #endif
122 
123 /**
124  * div64_u64 - unsigned 64bit divide with 64bit divisor
125  * @dividend:   64bit dividend
126  * @divisor:    64bit divisor
127  *
128  * This implementation is a modified version of the algorithm proposed
129  * by the book 'Hacker's Delight'.  The original source and full proof
130  * can be found here and is available for use without restriction.
131  *
132  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
133  */
134 #ifndef div64_u64
135 u64 div64_u64(u64 dividend, u64 divisor)
136 {
137         u32 high = divisor >> 32;
138         u64 quot;
139 
140         if (high == 0) {
141                 quot = div_u64(dividend, divisor);
142         } else {
143                 int n = 1 + fls(high);
144                 quot = div_u64(dividend >> n, divisor >> n);
145 
146                 if (quot != 0)
147                         quot--;
148                 if ((dividend - quot * divisor) >= divisor)
149                         quot++;
150         }
151 
152         return quot;
153 }
154 EXPORT_SYMBOL(div64_u64);
155 #endif
156 
157 /**
158  * div64_s64 - signed 64bit divide with 64bit divisor
159  * @dividend:   64bit dividend
160  * @divisor:    64bit divisor
161  */
162 #ifndef div64_s64
163 s64 div64_s64(s64 dividend, s64 divisor)
164 {
165         s64 quot, t;
166 
167         quot = div64_u64(abs(dividend), abs(divisor));
168         t = (dividend ^ divisor) >> 63;
169 
170         return (quot ^ t) - t;
171 }
172 EXPORT_SYMBOL(div64_s64);
173 #endif
174 
175 #endif /* BITS_PER_LONG == 32 */
176 
177 /*
178  * Iterative div/mod for use when dividend is not expected to be much
179  * bigger than divisor.
180  */
181 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
182 {
183         return __iter_div_u64_rem(dividend, divisor, remainder);
184 }
185 EXPORT_SYMBOL(iter_div_u64_rem);
186 

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