1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_GENERIC_DIV64_H
3 #define _ASM_GENERIC_DIV64_H
4 /*
5 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
6 * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h
7 *
8 * Optimization for constant divisors on 32-bit machines:
9 * Copyright (C) 2006-2015 Nicolas Pitre
10 *
11 * The semantics of do_div() is, in C++ notation, observing that the name
12 * is a function-like macro and the n parameter has the semantics of a C++
13 * reference:
14 *
15 * uint32_t do_div(uint64_t &n, uint32_t base)
16 * {
17 * uint32_t remainder = n % base;
18 * n = n / base;
19 * return remainder;
20 * }
21 *
22 * NOTE: macro parameter n is evaluated multiple times,
23 * beware of side effects!
24 */
25
26 #include <linux/types.h>
27 #include <linux/compiler.h>
28
29 #if BITS_PER_LONG == 64
30
31 /**
32 * do_div - returns 2 values: calculate remainder and update new dividend
33 * @n: uint64_t dividend (will be updated)
34 * @base: uint32_t divisor
35 *
36 * Summary:
37 * ``uint32_t remainder = n % base;``
38 * ``n = n / base;``
39 *
40 * Return: (uint32_t)remainder
41 *
42 * NOTE: macro parameter @n is evaluated multiple times,
43 * beware of side effects!
44 */
45 # define do_div(n,base) ({ \
46 uint32_t __base = (base); \
47 uint32_t __rem; \
48 __rem = ((uint64_t)(n)) % __base; \
49 (n) = ((uint64_t)(n)) / __base; \
50 __rem; \
51 })
52
53 #elif BITS_PER_LONG == 32
54
55 #include <linux/log2.h>
56
57 /*
58 * If the divisor happens to be constant, we determine the appropriate
59 * inverse at compile time to turn the division into a few inline
60 * multiplications which ought to be much faster.
61 *
62 * (It is unfortunate that gcc doesn't perform all this internally.)
63 */
64
65 #define __div64_const32(n, ___b) \
66 ({ \
67 /* \
68 * Multiplication by reciprocal of b: n / b = n * (p / b) / p \
69 * \
70 * We rely on the fact that most of this code gets optimized \
71 * away at compile time due to constant propagation and only \
72 * a few multiplication instructions should remain. \
73 * Hence this monstrous macro (static inline doesn't always \
74 * do the trick here). \
75 */ \
76 uint64_t ___res, ___x, ___t, ___m, ___n = (n); \
77 uint32_t ___p, ___bias; \
78 \
79 /* determine MSB of b */ \
80 ___p = 1 << ilog2(___b); \
81 \
82 /* compute m = ((p << 64) + b - 1) / b */ \
83 ___m = (~0ULL / ___b) * ___p; \
84 ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \
85 \
86 /* one less than the dividend with highest result */ \
87 ___x = ~0ULL / ___b * ___b - 1; \
88 \
89 /* test our ___m with res = m * x / (p << 64) */ \
90 ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32; \
91 ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \
92 ___res += (___x & 0xffffffff) * (___m >> 32); \
93 ___t = (___res < ___t) ? (1ULL << 32) : 0; \
94 ___res = (___res >> 32) + ___t; \
95 ___res += (___m >> 32) * (___x >> 32); \
96 ___res /= ___p; \
97 \
98 /* Now sanitize and optimize what we've got. */ \
99 if (~0ULL % (___b / (___b & -___b)) == 0) { \
100 /* special case, can be simplified to ... */ \
101 ___n /= (___b & -___b); \
102 ___m = ~0ULL / (___b / (___b & -___b)); \
103 ___p = 1; \
104 ___bias = 1; \
105 } else if (___res != ___x / ___b) { \
106 /* \
107 * We can't get away without a bias to compensate \
108 * for bit truncation errors. To avoid it we'd need an \
109 * additional bit to represent m which would overflow \
110 * a 64-bit variable. \
111 * \
112 * Instead we do m = p / b and n / b = (n * m + m) / p. \
113 */ \
114 ___bias = 1; \
115 /* Compute m = (p << 64) / b */ \
116 ___m = (~0ULL / ___b) * ___p; \
117 ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \
118 } else { \
119 /* \
120 * Reduce m / p, and try to clear bit 31 of m when \
121 * possible, otherwise that'll need extra overflow \
122 * handling later. \
123 */ \
124 uint32_t ___bits = -(___m & -___m); \
125 ___bits |= ___m >> 32; \
126 ___bits = (~___bits) << 1; \
127 /* \
128 * If ___bits == 0 then setting bit 31 is unavoidable. \
129 * Simply apply the maximum possible reduction in that \
130 * case. Otherwise the MSB of ___bits indicates the \
131 * best reduction we should apply. \
132 */ \
133 if (!___bits) { \
134 ___p /= (___m & -___m); \
135 ___m /= (___m & -___m); \
136 } else { \
137 ___p >>= ilog2(___bits); \
138 ___m >>= ilog2(___bits); \
139 } \
140 /* No bias needed. */ \
141 ___bias = 0; \
142 } \
143 \
144 /* \
145 * Now we have a combination of 2 conditions: \
146 * \
147 * 1) whether or not we need to apply a bias, and \
148 * \
149 * 2) whether or not there might be an overflow in the cross \
150 * product determined by (___m & ((1 << 63) | (1 << 31))). \
151 * \
152 * Select the best way to do (m_bias + m * n) / (1 << 64). \
153 * From now on there will be actual runtime code generated. \
154 */ \
155 ___res = __arch_xprod_64(___m, ___n, ___bias); \
156 \
157 ___res /= ___p; \
158 })
159
160 #ifndef __arch_xprod_64
161 /*
162 * Default C implementation for __arch_xprod_64()
163 *
164 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
165 * Semantic: retval = ((bias ? m : 0) + m * n) >> 64
166 *
167 * The product is a 128-bit value, scaled down to 64 bits.
168 * Assuming constant propagation to optimize away unused conditional code.
169 * Architectures may provide their own optimized assembly implementation.
170 */
171 static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
172 {
173 uint32_t m_lo = m;
174 uint32_t m_hi = m >> 32;
175 uint32_t n_lo = n;
176 uint32_t n_hi = n >> 32;
177 uint64_t res;
178 uint32_t res_lo, res_hi, tmp;
179
180 if (!bias) {
181 res = ((uint64_t)m_lo * n_lo) >> 32;
182 } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
183 /* there can't be any overflow here */
184 res = (m + (uint64_t)m_lo * n_lo) >> 32;
185 } else {
186 res = m + (uint64_t)m_lo * n_lo;
187 res_lo = res >> 32;
188 res_hi = (res_lo < m_hi);
189 res = res_lo | ((uint64_t)res_hi << 32);
190 }
191
192 if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
193 /* there can't be any overflow here */
194 res += (uint64_t)m_lo * n_hi;
195 res += (uint64_t)m_hi * n_lo;
196 res >>= 32;
197 } else {
198 res += (uint64_t)m_lo * n_hi;
199 tmp = res >> 32;
200 res += (uint64_t)m_hi * n_lo;
201 res_lo = res >> 32;
202 res_hi = (res_lo < tmp);
203 res = res_lo | ((uint64_t)res_hi << 32);
204 }
205
206 res += (uint64_t)m_hi * n_hi;
207
208 return res;
209 }
210 #endif
211
212 #ifndef __div64_32
213 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
214 #endif
215
216 /* The unnecessary pointer compare is there
217 * to check for type safety (n must be 64bit)
218 */
219 # define do_div(n,base) ({ \
220 uint32_t __base = (base); \
221 uint32_t __rem; \
222 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
223 if (__builtin_constant_p(__base) && \
224 is_power_of_2(__base)) { \
225 __rem = (n) & (__base - 1); \
226 (n) >>= ilog2(__base); \
227 } else if (__builtin_constant_p(__base) && \
228 __base != 0) { \
229 uint32_t __res_lo, __n_lo = (n); \
230 (n) = __div64_const32(n, __base); \
231 /* the remainder can be computed with 32-bit regs */ \
232 __res_lo = (n); \
233 __rem = __n_lo - __res_lo * __base; \
234 } else if (likely(((n) >> 32) == 0)) { \
235 __rem = (uint32_t)(n) % __base; \
236 (n) = (uint32_t)(n) / __base; \
237 } else { \
238 __rem = __div64_32(&(n), __base); \
239 } \
240 __rem; \
241 })
242
243 #else /* BITS_PER_LONG == ?? */
244
245 # error do_div() does not yet support the C64
246
247 #endif /* BITS_PER_LONG */
248
249 #endif /* _ASM_GENERIC_DIV64_H */
250
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