/* * arch/alpha/lib/ev6-divide.S * * 21264 version contributed by Rick Gorton * * 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