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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/compat.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 /*
29  * Don't instrument this function as it may be called from tracing code, since
30  * it needs to read the timer and this often requires calling do_div(), which
31  * calls this function.
32  */
__div64_32(u64 * n,u32 base)33 uint32_t __attribute__((weak, no_instrument_function)) __div64_32(u64 *n,
34 								  u32 base)
35 {
36 	u64 rem = *n;
37 	u64 b = base;
38 	u64 res, d = 1;
39 	u32 high = rem >> 32;
40 
41 	/* Reduce the thing a bit first */
42 	res = 0;
43 	if (high >= base) {
44 		high /= base;
45 		res = (u64)high << 32;
46 		rem -= (u64)(high * base) << 32;
47 	}
48 
49 	while ((int64_t)b > 0 && b < rem) {
50 		b = b+b;
51 		d = d+d;
52 	}
53 
54 	do {
55 		if (rem >= b) {
56 			rem -= b;
57 			res += d;
58 		}
59 		b >>= 1;
60 		d >>= 1;
61 	} while (d);
62 
63 	*n = res;
64 	return rem;
65 }
66 EXPORT_SYMBOL(__div64_32);
67 #endif
68 
69 #ifndef div_s64_rem
div_s64_rem(s64 dividend,s32 divisor,s32 * remainder)70 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
71 {
72 	u64 quotient;
73 
74 	if (dividend < 0) {
75 		quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
76 		*remainder = -*remainder;
77 		if (divisor > 0)
78 			quotient = -quotient;
79 	} else {
80 		quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
81 		if (divisor < 0)
82 			quotient = -quotient;
83 	}
84 	return quotient;
85 }
86 EXPORT_SYMBOL(div_s64_rem);
87 #endif
88 
89 /**
90  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
91  * @dividend:	64bit dividend
92  * @divisor:	64bit divisor
93  * @remainder:  64bit remainder
94  *
95  * This implementation is a comparable to algorithm used by div64_u64.
96  * But this operation, which includes math for calculating the remainder,
97  * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
98  * systems.
99  */
100 #ifndef div64_u64_rem
div64_u64_rem(u64 dividend,u64 divisor,u64 * remainder)101 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
102 {
103 	u32 high = divisor >> 32;
104 	u64 quot;
105 
106 	if (high == 0) {
107 		u32 rem32;
108 		quot = div_u64_rem(dividend, divisor, &rem32);
109 		*remainder = rem32;
110 	} else {
111 		int n = 1 + fls(high);
112 		quot = div_u64(dividend >> n, divisor >> n);
113 
114 		if (quot != 0)
115 			quot--;
116 
117 		*remainder = dividend - quot * divisor;
118 		if (*remainder >= divisor) {
119 			quot++;
120 			*remainder -= divisor;
121 		}
122 	}
123 
124 	return quot;
125 }
126 EXPORT_SYMBOL(div64_u64_rem);
127 #endif
128 
129 /**
130  * div64_u64 - unsigned 64bit divide with 64bit divisor
131  * @dividend:	64bit dividend
132  * @divisor:	64bit divisor
133  *
134  * This implementation is a modified version of the algorithm proposed
135  * by the book 'Hacker's Delight'.  The original source and full proof
136  * can be found here and is available for use without restriction.
137  *
138  * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
139  */
140 #ifndef div64_u64
div64_u64(u64 dividend,u64 divisor)141 u64 div64_u64(u64 dividend, u64 divisor)
142 {
143 	u32 high = divisor >> 32;
144 	u64 quot;
145 
146 	if (high == 0) {
147 		quot = div_u64(dividend, divisor);
148 	} else {
149 		int n = 1 + fls(high);
150 		quot = div_u64(dividend >> n, divisor >> n);
151 
152 		if (quot != 0)
153 			quot--;
154 		if ((dividend - quot * divisor) >= divisor)
155 			quot++;
156 	}
157 
158 	return quot;
159 }
160 EXPORT_SYMBOL(div64_u64);
161 #endif
162 
163 /**
164  * div64_s64 - signed 64bit divide with 64bit divisor
165  * @dividend:	64bit dividend
166  * @divisor:	64bit divisor
167  */
168 #ifndef div64_s64
div64_s64(s64 dividend,s64 divisor)169 s64 div64_s64(s64 dividend, s64 divisor)
170 {
171 	s64 quot, t;
172 
173 	quot = div64_u64(abs(dividend), abs(divisor));
174 	t = (dividend ^ divisor) >> 63;
175 
176 	return (quot ^ t) - t;
177 }
178 EXPORT_SYMBOL(div64_s64);
179 #endif
180 
181 #endif /* BITS_PER_LONG == 32 */
182 
183 /*
184  * Iterative div/mod for use when dividend is not expected to be much
185  * bigger than divisor.
186  */
iter_div_u64_rem(u64 dividend,u32 divisor,u64 * remainder)187 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
188 {
189 	return __iter_div_u64_rem(dividend, divisor, remainder);
190 }
191 EXPORT_SYMBOL(iter_div_u64_rem);
192