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. And yet only if compiling
61 * with a sufficiently recent gcc version to perform proper 64-bit constant
62 * propagation.
63 *
64 * (It is unfortunate that gcc doesn't perform all this internally.)
65 */
66
67 #ifndef __div64_const32_is_OK
68 #define __div64_const32_is_OK (__GNUC__ >= 4)
69 #endif
70
71 #define __div64_const32(n, ___b) \
72 ({ \
73 /* \
74 * Multiplication by reciprocal of b: n / b = n * (p / b) / p \
75 * \
76 * We rely on the fact that most of this code gets optimized \
77 * away at compile time due to constant propagation and only \
78 * a few multiplication instructions should remain. \
79 * Hence this monstrous macro (static inline doesn't always \
80 * do the trick here). \
81 */ \
82 uint64_t ___res, ___x, ___t, ___m, ___n = (n); \
83 uint32_t ___p, ___bias; \
84 \
85 /* determine MSB of b */ \
86 ___p = 1 << ilog2(___b); \
87 \
88 /* compute m = ((p << 64) + b - 1) / b */ \
89 ___m = (~0ULL / ___b) * ___p; \
90 ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \
91 \
92 /* one less than the dividend with highest result */ \
93 ___x = ~0ULL / ___b * ___b - 1; \
94 \
95 /* test our ___m with res = m * x / (p << 64) */ \
96 ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32; \
97 ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \
98 ___res += (___x & 0xffffffff) * (___m >> 32); \
99 ___t = (___res < ___t) ? (1ULL << 32) : 0; \
100 ___res = (___res >> 32) + ___t; \
101 ___res += (___m >> 32) * (___x >> 32); \
102 ___res /= ___p; \
103 \
104 /* Now sanitize and optimize what we've got. */ \
105 if (~0ULL % (___b / (___b & -___b)) == 0) { \
106 /* special case, can be simplified to ... */ \
107 ___n /= (___b & -___b); \
108 ___m = ~0ULL / (___b / (___b & -___b)); \
109 ___p = 1; \
110 ___bias = 1; \
111 } else if (___res != ___x / ___b) { \
112 /* \
113 * We can't get away without a bias to compensate \
114 * for bit truncation errors. To avoid it we'd need an \
115 * additional bit to represent m which would overflow \
116 * a 64-bit variable. \
117 * \
118 * Instead we do m = p / b and n / b = (n * m + m) / p. \
119 */ \
120 ___bias = 1; \
121 /* Compute m = (p << 64) / b */ \
122 ___m = (~0ULL / ___b) * ___p; \
123 ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \
124 } else { \
125 /* \
126 * Reduce m / p, and try to clear bit 31 of m when \
127 * possible, otherwise that'll need extra overflow \
128 * handling later. \
129 */ \
130 uint32_t ___bits = -(___m & -___m); \
131 ___bits |= ___m >> 32; \
132 ___bits = (~___bits) << 1; \
133 /* \
134 * If ___bits == 0 then setting bit 31 is unavoidable. \
135 * Simply apply the maximum possible reduction in that \
136 * case. Otherwise the MSB of ___bits indicates the \
137 * best reduction we should apply. \
138 */ \
139 if (!___bits) { \
140 ___p /= (___m & -___m); \
141 ___m /= (___m & -___m); \
142 } else { \
143 ___p >>= ilog2(___bits); \
144 ___m >>= ilog2(___bits); \
145 } \
146 /* No bias needed. */ \
147 ___bias = 0; \
148 } \
149 \
150 /* \
151 * Now we have a combination of 2 conditions: \
152 * \
153 * 1) whether or not we need to apply a bias, and \
154 * \
155 * 2) whether or not there might be an overflow in the cross \
156 * product determined by (___m & ((1 << 63) | (1 << 31))). \
157 * \
158 * Select the best way to do (m_bias + m * n) / (1 << 64). \
159 * From now on there will be actual runtime code generated. \
160 */ \
161 ___res = __arch_xprod_64(___m, ___n, ___bias); \
162 \
163 ___res /= ___p; \
164 })
165
166 #ifndef __arch_xprod_64
167 /*
168 * Default C implementation for __arch_xprod_64()
169 *
170 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
171 * Semantic: retval = ((bias ? m : 0) + m * n) >> 64
172 *
173 * The product is a 128-bit value, scaled down to 64 bits.
174 * Assuming constant propagation to optimize away unused conditional code.
175 * Architectures may provide their own optimized assembly implementation.
176 */
__arch_xprod_64(const uint64_t m,uint64_t n,bool bias)177 static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
178 {
179 uint32_t m_lo = m;
180 uint32_t m_hi = m >> 32;
181 uint32_t n_lo = n;
182 uint32_t n_hi = n >> 32;
183 uint64_t res;
184 uint32_t res_lo, res_hi, tmp;
185
186 if (!bias) {
187 res = ((uint64_t)m_lo * n_lo) >> 32;
188 } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
189 /* there can't be any overflow here */
190 res = (m + (uint64_t)m_lo * n_lo) >> 32;
191 } else {
192 res = m + (uint64_t)m_lo * n_lo;
193 res_lo = res >> 32;
194 res_hi = (res_lo < m_hi);
195 res = res_lo | ((uint64_t)res_hi << 32);
196 }
197
198 if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
199 /* there can't be any overflow here */
200 res += (uint64_t)m_lo * n_hi;
201 res += (uint64_t)m_hi * n_lo;
202 res >>= 32;
203 } else {
204 res += (uint64_t)m_lo * n_hi;
205 tmp = res >> 32;
206 res += (uint64_t)m_hi * n_lo;
207 res_lo = res >> 32;
208 res_hi = (res_lo < tmp);
209 res = res_lo | ((uint64_t)res_hi << 32);
210 }
211
212 res += (uint64_t)m_hi * n_hi;
213
214 return res;
215 }
216 #endif
217
218 #ifndef __div64_32
219 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
220 #endif
221
222 /* The unnecessary pointer compare is there
223 * to check for type safety (n must be 64bit)
224 */
225 # define do_div(n,base) ({ \
226 uint32_t __base = (base); \
227 uint32_t __rem; \
228 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
229 if (__builtin_constant_p(__base) && \
230 is_power_of_2(__base)) { \
231 __rem = (n) & (__base - 1); \
232 (n) >>= ilog2(__base); \
233 } else if (__div64_const32_is_OK && \
234 __builtin_constant_p(__base) && \
235 __base != 0) { \
236 uint32_t __res_lo, __n_lo = (n); \
237 (n) = __div64_const32(n, __base); \
238 /* the remainder can be computed with 32-bit regs */ \
239 __res_lo = (n); \
240 __rem = __n_lo - __res_lo * __base; \
241 } else if (likely(((n) >> 32) == 0)) { \
242 __rem = (uint32_t)(n) % __base; \
243 (n) = (uint32_t)(n) / __base; \
244 } else \
245 __rem = __div64_32(&(n), __base); \
246 __rem; \
247 })
248
249 #else /* BITS_PER_LONG == ?? */
250
251 # error do_div() does not yet support the C64
252
253 #endif /* BITS_PER_LONG */
254
255 #endif /* _ASM_GENERIC_DIV64_H */
256