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 96ufunction: 97 subq $30,STACK,$30 98 .frame $30,STACK,$23 99 .prologue 0 100 1017: 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 */ 1231: cmpult divisor,modulus,compare 124 s8addq divisor,$31,divisor 125 s8addq mask,$31,mask 126 bne compare,1b 127#else 1281: 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.. */ 1372: 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 1469: 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 168sfunction: 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 196