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Diffstat (limited to 'arch/alpha/lib/divide.S')
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diff --git a/arch/alpha/lib/divide.S b/arch/alpha/lib/divide.S new file mode 100644 index 000000000000..2d1a0484a99e --- /dev/null +++ b/arch/alpha/lib/divide.S | |||
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1 | /* | ||
2 | * arch/alpha/lib/divide.S | ||
3 | * | ||
4 | * (C) 1995 Linus Torvalds | ||
5 | * | ||
6 | * Alpha division.. | ||
7 | */ | ||
8 | |||
9 | /* | ||
10 | * The alpha chip doesn't provide hardware division, so we have to do it | ||
11 | * by hand. The compiler expects the functions | ||
12 | * | ||
13 | * __divqu: 64-bit unsigned long divide | ||
14 | * __remqu: 64-bit unsigned long remainder | ||
15 | * __divqs/__remqs: signed 64-bit | ||
16 | * __divlu/__remlu: unsigned 32-bit | ||
17 | * __divls/__remls: signed 32-bit | ||
18 | * | ||
19 | * These are not normal C functions: instead of the normal | ||
20 | * calling sequence, these expect their arguments in registers | ||
21 | * $24 and $25, and return the result in $27. Register $28 may | ||
22 | * be clobbered (assembly temporary), anything else must be saved. | ||
23 | * | ||
24 | * In short: painful. | ||
25 | * | ||
26 | * This is a rather simple bit-at-a-time algorithm: it's very good | ||
27 | * at dividing random 64-bit numbers, but the more usual case where | ||
28 | * the divisor is small is handled better by the DEC algorithm | ||
29 | * using lookup tables. This uses much less memory, though, and is | ||
30 | * nicer on the cache.. Besides, I don't know the copyright status | ||
31 | * of the DEC code. | ||
32 | */ | ||
33 | |||
34 | /* | ||
35 | * My temporaries: | ||
36 | * $0 - current bit | ||
37 | * $1 - shifted divisor | ||
38 | * $2 - modulus/quotient | ||
39 | * | ||
40 | * $23 - return address | ||
41 | * $24 - dividend | ||
42 | * $25 - divisor | ||
43 | * | ||
44 | * $27 - quotient/modulus | ||
45 | * $28 - compare status | ||
46 | */ | ||
47 | |||
48 | #define halt .long 0 | ||
49 | |||
50 | /* | ||
51 | * Select function type and registers | ||
52 | */ | ||
53 | #define mask $0 | ||
54 | #define divisor $1 | ||
55 | #define compare $28 | ||
56 | #define tmp1 $3 | ||
57 | #define tmp2 $4 | ||
58 | |||
59 | #ifdef DIV | ||
60 | #define DIV_ONLY(x,y...) x,##y | ||
61 | #define MOD_ONLY(x,y...) | ||
62 | #define func(x) __div##x | ||
63 | #define modulus $2 | ||
64 | #define quotient $27 | ||
65 | #define GETSIGN(x) xor $24,$25,x | ||
66 | #define STACK 48 | ||
67 | #else | ||
68 | #define DIV_ONLY(x,y...) | ||
69 | #define MOD_ONLY(x,y...) x,##y | ||
70 | #define func(x) __rem##x | ||
71 | #define modulus $27 | ||
72 | #define quotient $2 | ||
73 | #define GETSIGN(x) bis $24,$24,x | ||
74 | #define STACK 32 | ||
75 | #endif | ||
76 | |||
77 | /* | ||
78 | * For 32-bit operations, we need to extend to 64-bit | ||
79 | */ | ||
80 | #ifdef INTSIZE | ||
81 | #define ufunction func(lu) | ||
82 | #define sfunction func(l) | ||
83 | #define LONGIFY(x) zapnot x,15,x | ||
84 | #define SLONGIFY(x) addl x,0,x | ||
85 | #else | ||
86 | #define ufunction func(qu) | ||
87 | #define sfunction func(q) | ||
88 | #define LONGIFY(x) | ||
89 | #define SLONGIFY(x) | ||
90 | #endif | ||
91 | |||
92 | .set noat | ||
93 | .align 3 | ||
94 | .globl ufunction | ||
95 | .ent ufunction | ||
96 | ufunction: | ||
97 | subq $30,STACK,$30 | ||
98 | .frame $30,STACK,$23 | ||
99 | .prologue 0 | ||
100 | |||
101 | 7: stq $1, 0($30) | ||
102 | bis $25,$25,divisor | ||
103 | stq $2, 8($30) | ||
104 | bis $24,$24,modulus | ||
105 | stq $0,16($30) | ||
106 | bis $31,$31,quotient | ||
107 | LONGIFY(divisor) | ||
108 | stq tmp1,24($30) | ||
109 | LONGIFY(modulus) | ||
110 | bis $31,1,mask | ||
111 | DIV_ONLY(stq tmp2,32($30)) | ||
112 | beq divisor, 9f /* div by zero */ | ||
113 | |||
114 | #ifdef INTSIZE | ||
115 | /* | ||
116 | * shift divisor left, using 3-bit shifts for | ||
117 | * 32-bit divides as we can't overflow. Three-bit | ||
118 | * shifts will result in looping three times less | ||
119 | * here, but can result in two loops more later. | ||
120 | * Thus using a large shift isn't worth it (and | ||
121 | * s8add pairs better than a sll..) | ||
122 | */ | ||
123 | 1: cmpult divisor,modulus,compare | ||
124 | s8addq divisor,$31,divisor | ||
125 | s8addq mask,$31,mask | ||
126 | bne compare,1b | ||
127 | #else | ||
128 | 1: cmpult divisor,modulus,compare | ||
129 | blt divisor, 2f | ||
130 | addq divisor,divisor,divisor | ||
131 | addq mask,mask,mask | ||
132 | bne compare,1b | ||
133 | unop | ||
134 | #endif | ||
135 | |||
136 | /* ok, start to go right again.. */ | ||
137 | 2: DIV_ONLY(addq quotient,mask,tmp2) | ||
138 | srl mask,1,mask | ||
139 | cmpule divisor,modulus,compare | ||
140 | subq modulus,divisor,tmp1 | ||
141 | DIV_ONLY(cmovne compare,tmp2,quotient) | ||
142 | srl divisor,1,divisor | ||
143 | cmovne compare,tmp1,modulus | ||
144 | bne mask,2b | ||
145 | |||
146 | 9: ldq $1, 0($30) | ||
147 | ldq $2, 8($30) | ||
148 | ldq $0,16($30) | ||
149 | ldq tmp1,24($30) | ||
150 | DIV_ONLY(ldq tmp2,32($30)) | ||
151 | addq $30,STACK,$30 | ||
152 | ret $31,($23),1 | ||
153 | .end ufunction | ||
154 | |||
155 | /* | ||
156 | * Uhh.. Ugly signed division. I'd rather not have it at all, but | ||
157 | * it's needed in some circumstances. There are different ways to | ||
158 | * handle this, really. This does: | ||
159 | * -a / b = a / -b = -(a / b) | ||
160 | * -a % b = -(a % b) | ||
161 | * a % -b = a % b | ||
162 | * which is probably not the best solution, but at least should | ||
163 | * have the property that (x/y)*y + (x%y) = x. | ||
164 | */ | ||
165 | .align 3 | ||
166 | .globl sfunction | ||
167 | .ent sfunction | ||
168 | sfunction: | ||
169 | subq $30,STACK,$30 | ||
170 | .frame $30,STACK,$23 | ||
171 | .prologue 0 | ||
172 | bis $24,$25,$28 | ||
173 | SLONGIFY($28) | ||
174 | bge $28,7b | ||
175 | stq $24,0($30) | ||
176 | subq $31,$24,$28 | ||
177 | stq $25,8($30) | ||
178 | cmovlt $24,$28,$24 /* abs($24) */ | ||
179 | stq $23,16($30) | ||
180 | subq $31,$25,$28 | ||
181 | stq tmp1,24($30) | ||
182 | cmovlt $25,$28,$25 /* abs($25) */ | ||
183 | unop | ||
184 | bsr $23,ufunction | ||
185 | ldq $24,0($30) | ||
186 | ldq $25,8($30) | ||
187 | GETSIGN($28) | ||
188 | subq $31,$27,tmp1 | ||
189 | SLONGIFY($28) | ||
190 | ldq $23,16($30) | ||
191 | cmovlt $28,tmp1,$27 | ||
192 | ldq tmp1,24($30) | ||
193 | addq $30,STACK,$30 | ||
194 | ret $31,($23),1 | ||
195 | .end sfunction | ||