| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 |