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