0b5f881c3d85a252481f30dc713b60a91f5d7c9f
[linux-3.10.git] / include / asm-arm / div64.h
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 extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
228
229 #endif