1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * arch/alpha/lib/divide.S 4 * 5 * (C) 1995 Linus Torvalds 6 * 7 * Alpha division.. 8 */ 9 10 /* 11 * The alpha chip doesn't provide hardware division, so we have to do it 12 * by hand. The compiler expects the functions 13 * 14 * __divqu: 64-bit unsigned long divide 15 * __remqu: 64-bit unsigned long remainder 16 * __divqs/__remqs: signed 64-bit 17 * __divlu/__remlu: unsigned 32-bit 18 * __divls/__remls: signed 32-bit 19 * 20 * These are not normal C functions: instead of the normal 21 * calling sequence, these expect their arguments in registers 22 * $24 and $25, and return the result in $27. Register $28 may 23 * be clobbered (assembly temporary), anything else must be saved. 24 * 25 * In short: painful. 26 * 27 * This is a rather simple bit-at-a-time algorithm: it's very good 28 * at dividing random 64-bit numbers, but the more usual case where 29 * the divisor is small is handled better by the DEC algorithm 30 * using lookup tables. This uses much less memory, though, and is 31 * nicer on the cache.. Besides, I don't know the copyright status 32 * of the DEC code. 33 */ 34 35 /* 36 * My temporaries: 37 * $0 - current bit 38 * $1 - shifted divisor 39 * $2 - modulus/quotient 40 * 41 * $23 - return address 42 * $24 - dividend 43 * $25 - divisor 44 * 45 * $27 - quotient/modulus 46 * $28 - compare status 47 */ 48 49 #include <asm/export.h> 50 #define halt .long 0 51 52 /* 53 * Select function type and registers 54 */ 55 #define mask $0 56 #define divisor $1 57 #define compare $28 58 #define tmp1 $3 59 #define tmp2 $4 60 61 #ifdef DIV 62 #define DIV_ONLY(x,y...) x,##y 63 #define MOD_ONLY(x,y...) 64 #define func(x) __div##x 65 #define modulus $2 66 #define quotient $27 67 #define GETSIGN(x) xor $24,$25,x 68 #define STACK 48 69 #else 70 #define DIV_ONLY(x,y...) 71 #define MOD_ONLY(x,y...) x,##y 72 #define func(x) __rem##x 73 #define modulus $27 74 #define quotient $2 75 #define GETSIGN(x) bis $24,$24,x 76 #define STACK 32 77 #endif 78 79 /* 80 * For 32-bit operations, we need to extend to 64-bit 81 */ 82 #ifdef INTSIZE 83 #define ufunction func(lu) 84 #define sfunction func(l) 85 #define LONGIFY(x) zapnot x,15,x 86 #define SLONGIFY(x) addl x,0,x 87 #else 88 #define ufunction func(qu) 89 #define sfunction func(q) 90 #define LONGIFY(x) 91 #define SLONGIFY(x) 92 #endif 93 94 .set noat 95 .align 3 96 .globl ufunction 97 .ent ufunction 98 ufunction: 99 subq $30,STACK,$30 100 .frame $30,STACK,$23 101 .prologue 0 102 103 7: stq $1, 0($30) 104 bis $25,$25,divisor 105 stq $2, 8($30) 106 bis $24,$24,modulus 107 stq $0,16($30) 108 bis $31,$31,quotient 109 LONGIFY(divisor) 110 stq tmp1,24($30) 111 LONGIFY(modulus) 112 bis $31,1,mask 113 DIV_ONLY(stq tmp2,32($30)) 114 beq divisor, 9f /* div by zero */ 115 116 #ifdef INTSIZE 117 /* 118 * shift divisor left, using 3-bit shifts for 119 * 32-bit divides as we can't overflow. Three-bit 120 * shifts will result in looping three times less 121 * here, but can result in two loops more later. 122 * Thus using a large shift isn't worth it (and 123 * s8add pairs better than a sll..) 124 */ 125 1: cmpult divisor,modulus,compare 126 s8addq divisor,$31,divisor 127 s8addq mask,$31,mask 128 bne compare,1b 129 #else 130 1: cmpult divisor,modulus,compare 131 blt divisor, 2f 132 addq divisor,divisor,divisor 133 addq mask,mask,mask 134 bne compare,1b 135 unop 136 #endif 137 138 /* ok, start to go right again.. */ 139 2: DIV_ONLY(addq quotient,mask,tmp2) 140 srl mask,1,mask 141 cmpule divisor,modulus,compare 142 subq modulus,divisor,tmp1 143 DIV_ONLY(cmovne compare,tmp2,quotient) 144 srl divisor,1,divisor 145 cmovne compare,tmp1,modulus 146 bne mask,2b 147 148 9: ldq $1, 0($30) 149 ldq $2, 8($30) 150 ldq $0,16($30) 151 ldq tmp1,24($30) 152 DIV_ONLY(ldq tmp2,32($30)) 153 addq $30,STACK,$30 154 ret $31,($23),1 155 .end ufunction 156 EXPORT_SYMBOL(ufunction) 157 158 /* 159 * Uhh.. Ugly signed division. I'd rather not have it at all, but 160 * it's needed in some circumstances. There are different ways to 161 * handle this, really. This does: 162 * -a / b = a / -b = -(a / b) 163 * -a % b = -(a % b) 164 * a % -b = a % b 165 * which is probably not the best solution, but at least should 166 * have the property that (x/y)*y + (x%y) = x. 167 */ 168 .align 3 169 .globl sfunction 170 .ent sfunction 171 sfunction: 172 subq $30,STACK,$30 173 .frame $30,STACK,$23 174 .prologue 0 175 bis $24,$25,$28 176 SLONGIFY($28) 177 bge $28,7b 178 stq $24,0($30) 179 subq $31,$24,$28 180 stq $25,8($30) 181 cmovlt $24,$28,$24 /* abs($24) */ 182 stq $23,16($30) 183 subq $31,$25,$28 184 stq tmp1,24($30) 185 cmovlt $25,$28,$25 /* abs($25) */ 186 unop 187 bsr $23,ufunction 188 ldq $24,0($30) 189 ldq $25,8($30) 190 GETSIGN($28) 191 subq $31,$27,tmp1 192 SLONGIFY($28) 193 ldq $23,16($30) 194 cmovlt $28,tmp1,$27 195 ldq tmp1,24($30) 196 addq $30,STACK,$30 197 ret $31,($23),1 198 .end sfunction 199 EXPORT_SYMBOL(sfunction) 200