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-rw-r--r--arch/arm/include/asm/div64.h227
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diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
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1#ifndef __ASM_ARM_DIV64
2#define __ASM_ARM_DIV64
3
4#include <asm/system.h>
5#include <linux/types.h>
6
7/*
8 * The semantics of do_div() are:
9 *
10 * uint32_t do_div(uint64_t *n, uint32_t base)
11 * {
12 * uint32_t remainder = *n % base;
13 * *n = *n / base;
14 * return remainder;
15 * }
16 *
17 * In other words, a 64-bit dividend with a 32-bit divisor producing
18 * a 64-bit result and a 32-bit remainder. To accomplish this optimally
19 * we call a special __do_div64 helper with completely non standard
20 * calling convention for arguments and results (beware).
21 */
22
23#ifdef __ARMEB__
24#define __xh "r0"
25#define __xl "r1"
26#else
27#define __xl "r0"
28#define __xh "r1"
29#endif
30
31#define __do_div_asm(n, base) \
32({ \
33 register unsigned int __base asm("r4") = base; \
34 register unsigned long long __n asm("r0") = n; \
35 register unsigned long long __res asm("r2"); \
36 register unsigned int __rem asm(__xh); \
37 asm( __asmeq("%0", __xh) \
38 __asmeq("%1", "r2") \
39 __asmeq("%2", "r0") \
40 __asmeq("%3", "r4") \
41 "bl __do_div64" \
42 : "=r" (__rem), "=r" (__res) \
43 : "r" (__n), "r" (__base) \
44 : "ip", "lr", "cc"); \
45 n = __res; \
46 __rem; \
47})
48
49#if __GNUC__ < 4
50
51/*
52 * gcc versions earlier than 4.0 are simply too problematic for the
53 * optimized implementation below. First there is gcc PR 15089 that
54 * tend to trig on more complex constructs, spurious .global __udivsi3
55 * are inserted even if none of those symbols are referenced in the
56 * generated code, and those gcc versions are not able to do constant
57 * propagation on long long values anyway.
58 */
59#define do_div(n, base) __do_div_asm(n, base)
60
61#elif __GNUC__ >= 4
62
63#include <asm/bug.h>
64
65/*
66 * If the divisor happens to be constant, we determine the appropriate
67 * inverse at compile time to turn the division into a few inline
68 * multiplications instead which is much faster. And yet only if compiling
69 * for ARMv4 or higher (we need umull/umlal) and if the gcc version is
70 * sufficiently recent to perform proper long long constant propagation.
71 * (It is unfortunate that gcc doesn't perform all this internally.)
72 */
73#define do_div(n, base) \
74({ \
75 unsigned int __r, __b = (base); \
76 if (!__builtin_constant_p(__b) || __b == 0 || \
77 (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) { \
78 /* non-constant divisor (or zero): slow path */ \
79 __r = __do_div_asm(n, __b); \
80 } else if ((__b & (__b - 1)) == 0) { \
81 /* Trivial: __b is constant and a power of 2 */ \
82 /* gcc does the right thing with this code. */ \
83 __r = n; \
84 __r &= (__b - 1); \
85 n /= __b; \
86 } else { \
87 /* Multiply by inverse of __b: n/b = n*(p/b)/p */ \
88 /* We rely on the fact that most of this code gets */ \
89 /* optimized away at compile time due to constant */ \
90 /* propagation and only a couple inline assembly */ \
91 /* instructions should remain. Better avoid any */ \
92 /* code construct that might prevent that. */ \
93 unsigned long long __res, __x, __t, __m, __n = n; \
94 unsigned int __c, __p, __z = 0; \
95 /* preserve low part of n for reminder computation */ \
96 __r = __n; \
97 /* determine number of bits to represent __b */ \
98 __p = 1 << __div64_fls(__b); \
99 /* compute __m = ((__p << 64) + __b - 1) / __b */ \
100 __m = (~0ULL / __b) * __p; \
101 __m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \
102 /* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */ \
103 __x = ~0ULL / __b * __b - 1; \
104 __res = (__m & 0xffffffff) * (__x & 0xffffffff); \
105 __res >>= 32; \
106 __res += (__m & 0xffffffff) * (__x >> 32); \
107 __t = __res; \
108 __res += (__x & 0xffffffff) * (__m >> 32); \
109 __t = (__res < __t) ? (1ULL << 32) : 0; \
110 __res = (__res >> 32) + __t; \
111 __res += (__m >> 32) * (__x >> 32); \
112 __res /= __p; \
113 /* Now sanitize and optimize what we've got. */ \
114 if (~0ULL % (__b / (__b & -__b)) == 0) { \
115 /* those cases can be simplified with: */ \
116 __n /= (__b & -__b); \
117 __m = ~0ULL / (__b / (__b & -__b)); \
118 __p = 1; \
119 __c = 1; \
120 } else if (__res != __x / __b) { \
121 /* We can't get away without a correction */ \
122 /* to compensate for bit truncation errors. */ \
123 /* To avoid it we'd need an additional bit */ \
124 /* to represent __m which would overflow it. */ \
125 /* Instead we do m=p/b and n/b=(n*m+m)/p. */ \
126 __c = 1; \
127 /* Compute __m = (__p << 64) / __b */ \
128 __m = (~0ULL / __b) * __p; \
129 __m += ((~0ULL % __b + 1) * __p) / __b; \
130 } else { \
131 /* Reduce __m/__p, and try to clear bit 31 */ \
132 /* of __m when possible otherwise that'll */ \
133 /* need extra overflow handling later. */ \
134 unsigned int __bits = -(__m & -__m); \
135 __bits |= __m >> 32; \
136 __bits = (~__bits) << 1; \
137 /* If __bits == 0 then setting bit 31 is */ \
138 /* unavoidable. Simply apply the maximum */ \
139 /* possible reduction in that case. */ \
140 /* Otherwise the MSB of __bits indicates the */ \
141 /* best reduction we should apply. */ \
142 if (!__bits) { \
143 __p /= (__m & -__m); \
144 __m /= (__m & -__m); \
145 } else { \
146 __p >>= __div64_fls(__bits); \
147 __m >>= __div64_fls(__bits); \
148 } \
149 /* No correction needed. */ \
150 __c = 0; \
151 } \
152 /* Now we have a combination of 2 conditions: */ \
153 /* 1) whether or not we need a correction (__c), and */ \
154 /* 2) whether or not there might be an overflow in */ \
155 /* the cross product (__m & ((1<<63) | (1<<31))) */ \
156 /* Select the best insn combination to perform the */ \
157 /* actual __m * __n / (__p << 64) operation. */ \
158 if (!__c) { \
159 asm ( "umull %Q0, %R0, %1, %Q2\n\t" \
160 "mov %Q0, #0" \
161 : "=&r" (__res) \
162 : "r" (__m), "r" (__n) \
163 : "cc" ); \
164 } else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
165 __res = __m; \
166 asm ( "umlal %Q0, %R0, %Q1, %Q2\n\t" \
167 "mov %Q0, #0" \
168 : "+r" (__res) \
169 : "r" (__m), "r" (__n) \
170 : "cc" ); \
171 } else { \
172 asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \
173 "cmn %Q0, %Q1\n\t" \
174 "adcs %R0, %R0, %R1\n\t" \
175 "adc %Q0, %3, #0" \
176 : "=&r" (__res) \
177 : "r" (__m), "r" (__n), "r" (__z) \
178 : "cc" ); \
179 } \
180 if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
181 asm ( "umlal %R0, %Q0, %R1, %Q2\n\t" \
182 "umlal %R0, %Q0, %Q1, %R2\n\t" \
183 "mov %R0, #0\n\t" \
184 "umlal %Q0, %R0, %R1, %R2" \
185 : "+r" (__res) \
186 : "r" (__m), "r" (__n) \
187 : "cc" ); \
188 } else { \
189 asm ( "umlal %R0, %Q0, %R2, %Q3\n\t" \
190 "umlal %R0, %1, %Q2, %R3\n\t" \
191 "mov %R0, #0\n\t" \
192 "adds %Q0, %1, %Q0\n\t" \
193 "adc %R0, %R0, #0\n\t" \
194 "umlal %Q0, %R0, %R2, %R3" \
195 : "+r" (__res), "+r" (__z) \
196 : "r" (__m), "r" (__n) \
197 : "cc" ); \
198 } \
199 __res /= __p; \
200 /* The reminder can be computed with 32-bit regs */ \
201 /* only, and gcc is good at that. */ \
202 { \
203 unsigned int __res0 = __res; \
204 unsigned int __b0 = __b; \
205 __r -= __res0 * __b0; \
206 } \
207 /* BUG_ON(__r >= __b || __res * __b + __r != n); */ \
208 n = __res; \
209 } \
210 __r; \
211})
212
213/* our own fls implementation to make sure constant propagation is fine */
214#define __div64_fls(bits) \
215({ \
216 unsigned int __left = (bits), __nr = 0; \
217 if (__left & 0xffff0000) __nr += 16, __left >>= 16; \
218 if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \
219 if (__left & 0x000000f0) __nr += 4, __left >>= 4; \
220 if (__left & 0x0000000c) __nr += 2, __left >>= 2; \
221 if (__left & 0x00000002) __nr += 1; \
222 __nr; \
223})
224
225#endif
226
227#endif
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