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