/*
   * 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