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-rw-r--r--include/asm-arm/div64.h180
1 files changed, 179 insertions, 1 deletions
diff --git a/include/asm-arm/div64.h b/include/asm-arm/div64.h
index 3682616804ca..37e0a96e8789 100644
--- a/include/asm-arm/div64.h
+++ b/include/asm-arm/div64.h
@@ -27,7 +27,7 @@
27#define __xh "r1" 27#define __xh "r1"
28#endif 28#endif
29 29
30#define do_div(n,base) \ 30#define __do_div_asm(n, base) \
31({ \ 31({ \
32 register unsigned int __base asm("r4") = base; \ 32 register unsigned int __base asm("r4") = base; \
33 register unsigned long long __n asm("r0") = n; \ 33 register unsigned long long __n asm("r0") = n; \
@@ -45,4 +45,182 @@
45 __rem; \ 45 __rem; \
46}) 46})
47 47
48#if __GNUC__ < 4
49
50/*
51 * gcc versions earlier than 4.0 are simply too problematic for the
52 * optimized implementation below. First there is gcc PR 15089 that
53 * tend to trig on more complex constructs, spurious .global __udivsi3
54 * are inserted even if none of those symbols are referenced in the
55 * generated code, and those gcc versions are not able to do constant
56 * propagation on long long values anyway.
57 */
58#define do_div(n, base) __do_div_asm(n, base)
59
60#elif __GNUC__ >= 4
61
62#include <asm/bug.h>
63
64/*
65 * If the divisor happens to be constant, we determine the appropriate
66 * inverse at compile time to turn the division into a few inline
67 * multiplications instead which is much faster. And yet only if compiling
68 * for ARMv4 or higher (we need umull/umlal) and if the gcc version is
69 * sufficiently recent to perform proper long long constant propagation.
70 * (It is unfortunate that gcc doesn't perform all this internally.)
71 */
72#define do_div(n, base) \
73({ \
74 unsigned int __r, __b = (base); \
75 if (!__builtin_constant_p(__b) || __b == 0 || \
76 (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) { \
77 /* non-constant divisor (or zero): slow path */ \
78 __r = __do_div_asm(n, __b); \
79 } else if ((__b & (__b - 1)) == 0) { \
80 /* Trivial: __b is constant and a power of 2 */ \
81 /* gcc does the right thing with this code. */ \
82 __r = n; \
83 __r &= (__b - 1); \
84 n /= __b; \
85 } else { \
86 /* Multiply by inverse of __b: n/b = n*(p/b)/p */ \
87 /* We rely on the fact that most of this code gets */ \
88 /* optimized away at compile time due to constant */ \
89 /* propagation and only a couple inline assembly */ \
90 /* instructions should remain. Better avoid any */ \
91 /* code construct that might prevent that. */ \
92 unsigned long long __res, __x, __t, __m, __n = n; \
93 unsigned int __c, __p, __z = 0; \
94 /* preserve low part of n for reminder computation */ \
95 __r = __n; \
96 /* determine number of bits to represent __b */ \
97 __p = 1 << __div64_fls(__b); \
98 /* compute __m = ((__p << 64) + __b - 1) / __b */ \
99 __m = (~0ULL / __b) * __p; \
100 __m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \
101 /* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */ \
102 __x = ~0ULL / __b * __b - 1; \
103 __res = (__m & 0xffffffff) * (__x & 0xffffffff); \
104 __res >>= 32; \
105 __res += (__m & 0xffffffff) * (__x >> 32); \
106 __t = __res; \
107 __res += (__x & 0xffffffff) * (__m >> 32); \
108 __t = (__res < __t) ? (1ULL << 32) : 0; \
109 __res = (__res >> 32) + __t; \
110 __res += (__m >> 32) * (__x >> 32); \
111 __res /= __p; \
112 /* Now sanitize and optimize what we've got. */ \
113 if (~0ULL % (__b / (__b & -__b)) == 0) { \
114 /* those cases can be simplified with: */ \
115 __n /= (__b & -__b); \
116 __m = ~0ULL / (__b / (__b & -__b)); \
117 __p = 1; \
118 __c = 1; \
119 } else if (__res != __x / __b) { \
120 /* We can't get away without a correction */ \
121 /* to compensate for bit truncation errors. */ \
122 /* To avoid it we'd need an additional bit */ \
123 /* to represent __m which would overflow it. */ \
124 /* Instead we do m=p/b and n/b=(n*m+m)/p. */ \
125 __c = 1; \
126 /* Compute __m = (__p << 64) / __b */ \
127 __m = (~0ULL / __b) * __p; \
128 __m += ((~0ULL % __b + 1) * __p) / __b; \
129 } else { \
130 /* Reduce __m/__p, and try to clear bit 31 */ \
131 /* of __m when possible otherwise that'll */ \
132 /* need extra overflow handling later. */ \
133 unsigned int __bits = -(__m & -__m); \
134 __bits |= __m >> 32; \
135 __bits = (~__bits) << 1; \
136 /* If __bits == 0 then setting bit 31 is */ \
137 /* unavoidable. Simply apply the maximum */ \
138 /* possible reduction in that case. */ \
139 /* Otherwise the MSB of __bits indicates the */ \
140 /* best reduction we should apply. */ \
141 if (!__bits) { \
142 __p /= (__m & -__m); \
143 __m /= (__m & -__m); \
144 } else { \
145 __p >>= __div64_fls(__bits); \
146 __m >>= __div64_fls(__bits); \
147 } \
148 /* No correction needed. */ \
149 __c = 0; \
150 } \
151 /* Now we have a combination of 2 conditions: */ \
152 /* 1) whether or not we need a correction (__c), and */ \
153 /* 2) whether or not there might be an overflow in */ \
154 /* the cross product (__m & ((1<<63) | (1<<31))) */ \
155 /* Select the best insn combination to perform the */ \
156 /* actual __m * __n / (__p << 64) operation. */ \
157 if (!__c) { \
158 asm ( "umull %Q0, %R0, %1, %Q2\n\t" \
159 "mov %Q0, #0" \
160 : "=&r" (__res) \
161 : "r" (__m), "r" (__n) \
162 : "cc" ); \
163 } else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
164 __res = __m; \
165 asm ( "umlal %Q0, %R0, %Q1, %Q2\n\t" \
166 "mov %Q0, #0" \
167 : "+r" (__res) \
168 : "r" (__m), "r" (__n) \
169 : "cc" ); \
170 } else { \
171 asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \
172 "cmn %Q0, %Q1\n\t" \
173 "adcs %R0, %R0, %R1\n\t" \
174 "adc %Q0, %3, #0" \
175 : "=&r" (__res) \
176 : "r" (__m), "r" (__n), "r" (__z) \
177 : "cc" ); \
178 } \
179 if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
180 asm ( "umlal %R0, %Q0, %R1, %Q2\n\t" \
181 "umlal %R0, %Q0, %Q1, %R2\n\t" \
182 "mov %R0, #0\n\t" \
183 "umlal %Q0, %R0, %R1, %R2" \
184 : "+r" (__res) \
185 : "r" (__m), "r" (__n) \
186 : "cc" ); \
187 } else { \
188 asm ( "umlal %R0, %Q0, %R2, %Q3\n\t" \
189 "umlal %R0, %1, %Q2, %R3\n\t" \
190 "mov %R0, #0\n\t" \
191 "adds %Q0, %1, %Q0\n\t" \
192 "adc %R0, %R0, #0\n\t" \
193 "umlal %Q0, %R0, %R2, %R3" \
194 : "+r" (__res), "+r" (__z) \
195 : "r" (__m), "r" (__n) \
196 : "cc" ); \
197 } \
198 __res /= __p; \
199 /* The reminder can be computed with 32-bit regs */ \
200 /* only, and gcc is good at that. */ \
201 { \
202 unsigned int __res0 = __res; \
203 unsigned int __b0 = __b; \
204 __r -= __res0 * __b0; \
205 } \
206 /* BUG_ON(__r >= __b || __res * __b + __r != n); */ \
207 n = __res; \
208 } \
209 __r; \
210})
211
212/* our own fls implementation to make sure constant propagation is fine */
213#define __div64_fls(bits) \
214({ \
215 unsigned int __left = (bits), __nr = 0; \
216 if (__left & 0xffff0000) __nr += 16, __left >>= 16; \
217 if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \
218 if (__left & 0x000000f0) __nr += 4, __left >>= 4; \
219 if (__left & 0x0000000c) __nr += 2, __left >>= 2; \
220 if (__left & 0x00000002) __nr += 1; \
221 __nr; \
222})
223
224#endif
225
48#endif 226#endif
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