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Diffstat (limited to 'arch/alpha/lib/divide.S')
| -rw-r--r-- | arch/alpha/lib/divide.S | 199 |
1 files changed, 199 insertions, 0 deletions
diff --git a/arch/alpha/lib/divide.S b/arch/alpha/lib/divide.S new file mode 100644 index 0000000000..db01840d76 --- /dev/null +++ b/arch/alpha/lib/divide.S @@ -0,0 +1,199 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * arch/alpha/lib/divide.S + * + * (C) 1995 Linus Torvalds + * + * Alpha division.. + */ + +/* + * The alpha chip doesn't provide hardware division, so we have to do it + * by hand. The compiler expects the functions + * + * __divqu: 64-bit unsigned long divide + * __remqu: 64-bit unsigned long remainder + * __divqs/__remqs: signed 64-bit + * __divlu/__remlu: unsigned 32-bit + * __divls/__remls: signed 32-bit + * + * These are not normal C functions: instead of the normal + * calling sequence, these expect their arguments in registers + * $24 and $25, and return the result in $27. Register $28 may + * be clobbered (assembly temporary), anything else must be saved. + * + * In short: painful. + * + * This is a rather simple bit-at-a-time algorithm: it's very good + * at dividing random 64-bit numbers, but the more usual case where + * the divisor is small is handled better by the DEC algorithm + * using lookup tables. This uses much less memory, though, and is + * nicer on the cache.. Besides, I don't know the copyright status + * of the DEC code. + */ + +/* + * My temporaries: + * $0 - current bit + * $1 - shifted divisor + * $2 - modulus/quotient + * + * $23 - return address + * $24 - dividend + * $25 - divisor + * + * $27 - quotient/modulus + * $28 - compare status + */ + +#include <linux/export.h> +#define halt .long 0 + +/* + * Select function type and registers + */ +#define mask $0 +#define divisor $1 +#define compare $28 +#define tmp1 $3 +#define tmp2 $4 + +#ifdef DIV +#define DIV_ONLY(x,y...) x,##y +#define MOD_ONLY(x,y...) +#define func(x) __div##x +#define modulus $2 +#define quotient $27 +#define GETSIGN(x) xor $24,$25,x +#define STACK 48 +#else +#define DIV_ONLY(x,y...) +#define MOD_ONLY(x,y...) x,##y +#define func(x) __rem##x +#define modulus $27 +#define quotient $2 +#define GETSIGN(x) bis $24,$24,x +#define STACK 32 +#endif + +/* + * For 32-bit operations, we need to extend to 64-bit + */ +#ifdef INTSIZE +#define ufunction func(lu) +#define sfunction func(l) +#define LONGIFY(x) zapnot x,15,x +#define SLONGIFY(x) addl x,0,x +#else +#define ufunction func(qu) +#define sfunction func(q) +#define LONGIFY(x) +#define SLONGIFY(x) +#endif + +.set noat +.align 3 +.globl ufunction +.ent ufunction +ufunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + +7: stq $1, 0($30) + bis $25,$25,divisor + stq $2, 8($30) + bis $24,$24,modulus + stq $0,16($30) + bis $31,$31,quotient + LONGIFY(divisor) + stq tmp1,24($30) + LONGIFY(modulus) + bis $31,1,mask + DIV_ONLY(stq tmp2,32($30)) + beq divisor, 9f /* div by zero */ + +#ifdef INTSIZE + /* + * shift divisor left, using 3-bit shifts for + * 32-bit divides as we can't overflow. Three-bit + * shifts will result in looping three times less + * here, but can result in two loops more later. + * Thus using a large shift isn't worth it (and + * s8add pairs better than a sll..) + */ +1: cmpult divisor,modulus,compare + s8addq divisor,$31,divisor + s8addq mask,$31,mask + bne compare,1b +#else +1: cmpult divisor,modulus,compare + blt divisor, 2f + addq divisor,divisor,divisor + addq mask,mask,mask + bne compare,1b + unop +#endif + + /* ok, start to go right again.. */ +2: DIV_ONLY(addq quotient,mask,tmp2) + srl mask,1,mask + cmpule divisor,modulus,compare + subq modulus,divisor,tmp1 + DIV_ONLY(cmovne compare,tmp2,quotient) + srl divisor,1,divisor + cmovne compare,tmp1,modulus + bne mask,2b + +9: ldq $1, 0($30) + ldq $2, 8($30) + ldq $0,16($30) + ldq tmp1,24($30) + DIV_ONLY(ldq tmp2,32($30)) + addq $30,STACK,$30 + ret $31,($23),1 + .end ufunction +EXPORT_SYMBOL(ufunction) + +/* + * Uhh.. Ugly signed division. I'd rather not have it at all, but + * it's needed in some circumstances. There are different ways to + * handle this, really. This does: + * -a / b = a / -b = -(a / b) + * -a % b = -(a % b) + * a % -b = a % b + * which is probably not the best solution, but at least should + * have the property that (x/y)*y + (x%y) = x. + */ +.align 3 +.globl sfunction +.ent sfunction +sfunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + bis $24,$25,$28 + SLONGIFY($28) + bge $28,7b + stq $24,0($30) + subq $31,$24,$28 + stq $25,8($30) + cmovlt $24,$28,$24 /* abs($24) */ + stq $23,16($30) + subq $31,$25,$28 + stq tmp1,24($30) + cmovlt $25,$28,$25 /* abs($25) */ + unop + bsr $23,ufunction + ldq $24,0($30) + ldq $25,8($30) + GETSIGN($28) + subq $31,$27,tmp1 + SLONGIFY($28) + ldq $23,16($30) + cmovlt $28,tmp1,$27 + ldq tmp1,24($30) + addq $30,STACK,$30 + ret $31,($23),1 + .end sfunction +EXPORT_SYMBOL(sfunction) |