gfiber / kernel / skids / 105b4715ac1bd9139dcb2c40b9f4dafb1c3f4bae / . / arch / alpha / lib / ev6-divide.S

/* | |

* arch/alpha/lib/ev6-divide.S | |

* | |

* 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> | |

* | |

* 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 | |

* | |

* Much of the information about 21264 scheduling/coding comes from: | |

* Compiler Writer's Guide for the Alpha 21264 | |

* abbreviated as 'CWG' in other comments here | |

* ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html | |

* Scheduling notation: | |

* E - either cluster | |

* U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 | |

* L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 | |

* Try not to change the actual algorithm if possible for consistency. | |

*/ | |

#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 4 | |

.globl ufunction | |

.ent ufunction | |

ufunction: | |

subq $30,STACK,$30 # E : | |

.frame $30,STACK,$23 | |

.prologue 0 | |

7: stq $1, 0($30) # L : | |

bis $25,$25,divisor # E : | |

stq $2, 8($30) # L : L U L U | |

bis $24,$24,modulus # E : | |

stq $0,16($30) # L : | |

bis $31,$31,quotient # E : | |

LONGIFY(divisor) # E : U L L U | |

stq tmp1,24($30) # L : | |

LONGIFY(modulus) # E : | |

bis $31,1,mask # E : | |

DIV_ONLY(stq tmp2,32($30)) # L : L U U L | |

beq divisor, 9f /* div by zero */ | |

/* | |

* In spite of the DIV_ONLY being either a non-instruction | |

* or an actual stq, the addition of the .align directive | |

* below ensures that label 1 is going to be nicely aligned | |

*/ | |

.align 4 | |

#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 # E : | |

s8addq divisor,$31,divisor # E : | |

s8addq mask,$31,mask # E : | |

bne compare,1b # U : U L U L | |

#else | |

1: cmpult divisor,modulus,compare # E : | |

nop # E : | |

nop # E : | |

blt divisor, 2f # U : U L U L | |

addq divisor,divisor,divisor # E : | |

addq mask,mask,mask # E : | |

unop # E : | |

bne compare,1b # U : U L U L | |

#endif | |

/* ok, start to go right again.. */ | |

2: | |

/* | |

* Keep things nicely bundled... use a nop instead of not | |

* having an instruction for DIV_ONLY | |

*/ | |

#ifdef DIV | |

DIV_ONLY(addq quotient,mask,tmp2) # E : | |

#else | |

nop # E : | |

#endif | |

srl mask,1,mask # U : | |

cmpule divisor,modulus,compare # E : | |

subq modulus,divisor,tmp1 # E : | |

#ifdef DIV | |

DIV_ONLY(cmovne compare,tmp2,quotient) # E : Latency 2, extra map slot | |

nop # E : as part of the cmovne | |

srl divisor,1,divisor # U : | |

nop # E : L U L U | |

nop # E : | |

cmovne compare,tmp1,modulus # E : Latency 2, extra map slot | |

nop # E : as part of the cmovne | |

bne mask,2b # U : U L U L | |

#else | |

srl divisor,1,divisor # U : | |

cmovne compare,tmp1,modulus # E : Latency 2, extra map slot | |

nop # E : as part of the cmovne | |

bne mask,2b # U : U L L U | |

#endif | |

9: ldq $1, 0($30) # L : | |

ldq $2, 8($30) # L : | |

nop # E : | |

nop # E : U U L L | |

ldq $0,16($30) # L : | |

ldq tmp1,24($30) # L : | |

nop # E : | |

nop # E : | |

#ifdef DIV | |

DIV_ONLY(ldq tmp2,32($30)) # L : | |

#else | |

nop # E : | |

#endif | |

addq $30,STACK,$30 # E : | |

ret $31,($23),1 # L0 : L U U L | |

.end 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 4 | |

.globl sfunction | |

.ent sfunction | |

sfunction: | |

subq $30,STACK,$30 # E : | |

.frame $30,STACK,$23 | |

.prologue 0 | |

bis $24,$25,$28 # E : | |

SLONGIFY($28) # E : | |

bge $28,7b # U : | |

stq $24,0($30) # L : | |

subq $31,$24,$28 # E : | |

stq $25,8($30) # L : | |

nop # E : U L U L | |

cmovlt $24,$28,$24 /* abs($24) */ # E : Latency 2, extra map slot | |

nop # E : as part of the cmov | |

stq $23,16($30) # L : | |

subq $31,$25,$28 # E : U L U L | |

stq tmp1,24($30) # L : | |

cmovlt $25,$28,$25 /* abs($25) */ # E : Latency 2, extra map slot | |

nop # E : | |

bsr $23,ufunction # L0: L U L U | |

ldq $24,0($30) # L : | |

ldq $25,8($30) # L : | |

GETSIGN($28) # E : | |

subq $31,$27,tmp1 # E : U U L L | |

SLONGIFY($28) # E : | |

ldq $23,16($30) # L : | |

cmovlt $28,tmp1,$27 # E : Latency 2, extra map slot | |

nop # E : U L L U : as part of the cmov | |

ldq tmp1,24($30) # L : | |

nop # E : as part of the cmov | |

addq $30,STACK,$30 # E : | |

ret $31,($23),1 # L0 : L U U L | |

.end sfunction |