decbin.s

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

//  2n.(negative exp)
//   2. Check the digits in lwords 3 and 2 in descending order.
//   3. Add one for each zero encountered until a non-zero digit.
//   4. Add the count to the exp.
//   5. Check if the exp has crossed zero in #3 above; clear SE.
//   6. Divide the mantissa by 10**count.
//
//  *Why 27?  If the adjusted exponent is within -28 < expA < 28, than
//   any adjustment due to append/strip zeros will drive the resultant
//   exponent towards zero.  Since all pwrten constants with a power
//   of 27 or less are exact, there is no need to use this routine to
//   attempt to lessen the resultant exponent.
//
// Register usage:
//
//  ap_st_z:
//	(*)  d0: temp digit storage
//	(*)  d1: zero count
//	(*)  d2: digit count
//	(*)  d3: offset pointer
//	( )  d4: first word of bcd
//	(*)  d5: lword counter
//	( )  a0: pointer to working bcd value
//	( )  FP_SCR1: working copy of original bcd value
//	( )  L_SCR1: copy of original exponent word
//
//
// First check the absolute value of the exponent to see if this
// routine is necessary.  If so, then check the sign of the exponent
// and do append (+) or strip (-) zeros accordingly.
// This section handles a positive adjusted exponent.
//
ap_st_z:
	movel	L_SCR1(%a6),%d1	//load expA for range test
	cmpl	#27,%d1		//test is with 27
	ble	pwrten		//if abs(expA) <28, skip ap/st zeros
	btst	#30,(%a0)	//check sign of exp
	bne	ap_st_n		//if neg, go to neg side
	clrl	%d1		//zero count reg
	movel	(%a0),%d4		//load lword 1 to d4
	bfextu	%d4{#28:#4},%d0	//get M16 in d0
	bnes	ap_p_fx		//if M16 is non-zero, go fix exp
	addql	#1,%d1		//inc zero count
	moveql	#1,%d5		//init lword counter
	movel	(%a0,%d5.L*4),%d4	//get lword 2 to d4
	bnes	ap_p_cl		//if lw 2 is zero, skip it
	addql	#8,%d1		//and inc count by 8
	addql	#1,%d5		//inc lword counter
	movel	(%a0,%d5.L*4),%d4	//get lword 3 to d4
ap_p_cl:
	clrl	%d3		//init offset reg
	moveql	#7,%d2		//init digit counter
ap_p_gd:
	bfextu	%d4{%d3:#4},%d0	//get digit
	bnes	ap_p_fx		//if non-zero, go to fix exp
	addql	#4,%d3		//point to next digit
	addql	#1,%d1		//inc digit counter
	dbf	%d2,ap_p_gd	//get next digit
ap_p_fx:
	movel	%d1,%d0		//copy counter to d2
	movel	L_SCR1(%a6),%d1	//get adjusted exp from memory
	subl	%d0,%d1		//subtract count from exp
	bges	ap_p_fm		//if still pos, go to pwrten
	negl	%d1		//now its neg; get abs
	movel	(%a0),%d4		//load lword 1 to d4
	orl	#0x40000000,%d4	// and set SE in d4
	orl	#0x40000000,(%a0)	// and in memory
//
// Calculate the mantissa multiplier to compensate for the striping of
// zeros from the mantissa.
//
ap_p_fm:
	movel	#PTENRN,%a1	//get address of power-of-ten table
	clrl	%d3		//init table index
	fmoves	FONE,%fp1	//init fp1 to 1
	moveql	#3,%d2		//init d2 to count bits in counter
ap_p_el:
	asrl	#1,%d0		//shift lsb into carry
	bccs	ap_p_en		//if 1, mul fp1 by pwrten factor
	fmulx	(%a1,%d3),%fp1	//mul by 10**(d3_bit_no)
ap_p_en:
	addl	#12,%d3		//inc d3 to next rtable entry
	tstl	%d0		//check if d0 is zero
	bnes	ap_p_el		//if not, get next bit
	fmulx	%fp1,%fp0		//mul mantissa by 10**(no_bits_shifted)
	bra	pwrten		//go calc pwrten
//
// This section handles a negative adjusted exponent.
//
ap_st_n:
	clrl	%d1		//clr counter
	moveql	#2,%d5		//set up d5 to point to lword 3
	movel	(%a0,%d5.L*4),%d4	//get lword 3
	bnes	ap_n_cl		//if not zero, check digits
	subl	#1,%d5		//dec d5 to point to lword 2
	addql	#8,%d1		//inc counter by 8
	movel	(%a0,%d5.L*4),%d4	//get lword 2
ap_n_cl:
	movel	#28,%d3		//point to last digit
	moveql	#7,%d2		//init digit counter
ap_n_gd:
	bfextu	%d4{%d3:#4},%d0	//get digit
	bnes	ap_n_fx		//if non-zero, go to exp fix
	subql	#4,%d3		//point to previous digit
	addql	#1,%d1		//inc digit counter
	dbf	%d2,ap_n_gd	//get next digit
ap_n_fx:
	movel	%d1,%d0		//copy counter to d0
	movel	L_SCR1(%a6),%d1	//get adjusted exp from memory
	subl	%d0,%d1		//subtract count from exp
	bgts	ap_n_fm		//if still pos, go fix mantissa
	negl	%d1		//take abs of exp and clr SE
	movel	(%a0),%d4		//load lword 1 to d4
	andl	#0xbfffffff,%d4	// and clr SE in d4
	andl	#0xbfffffff,(%a0)	// and in memory
//
// Calculate the mantissa multiplier to compensate for the appending of
// zeros to the mantissa.
//
ap_n_fm:
	movel	#PTENRN,%a1	//get address of power-of-ten table
	clrl	%d3		//init table index
	fmoves	FONE,%fp1	//init fp1 to 1
	moveql	#3,%d2		//init d2 to count bits in counter
ap_n_el:
	asrl	#1,%d0		//shift lsb into carry
	bccs	ap_n_en		//if 1, mul fp1 by pwrten factor
	fmulx	(%a1,%d3),%fp1	//mul by 10**(d3_bit_no)
ap_n_en:
	addl	#12,%d3		//inc d3 to next rtable entry
	tstl	%d0		//check if d0 is zero
	bnes	ap_n_el		//if not, get next bit
	fdivx	%fp1,%fp0		//div mantissa by 10**(no_bits_shifted)
//
//
// Calculate power-of-ten factor from adjusted and shifted exponent.
//
// Register usage:
//
//  pwrten:
//	(*)  d0: temp
//	( )  d1: exponent
//	(*)  d2: {FPCR[6:5],SM,SE} as index in RTABLE; temp
//	(*)  d3: FPCR work copy
//	( )  d4: first word of bcd
//	(*)  a1: RTABLE pointer
//  calc_p:
//	(*)  d0: temp
//	( )  d1: exponent
//	(*)  d3: PWRTxx table index
//	( )  a0: pointer to working copy of bcd
//	(*)  a1: PWRTxx pointer
//	(*) fp1: power-of-ten accumulator
//
// Pwrten calculates the exponent factor in the selected rounding mode
// according to the following table:
//	
//	Sign of Mant  Sign of Exp  Rounding Mode  PWRTEN Rounding Mode
//
//	ANY	  ANY	RN	RN
//
//	 +	   +	RP	RP
//	 -	   +	RP	RM
//	 +	   -	RP	RM
//	 -	   -	RP	RP
//
//	 +	   +	RM	RM
//	 -	   +	RM	RP
//	 +	   -	RM	RP
//	 -	   -	RM	RM
//
//	 +	   +	RZ	RM
//	 -	   +	RZ	RM
//	 +	   -	RZ	RP
//	 -	   -	RZ	RP
//
//
pwrten:
	movel	USER_FPCR(%a6),%d3 //get user's FPCR
	bfextu	%d3{#26:#2},%d2	//isolate rounding mode bits
	movel	(%a0),%d4		//reload 1st bcd word to d4
	asll	#2,%d2		//format d2 to be
	bfextu	%d4{#0:#2},%d0	// {FPCR[6],FPCR[5],SM,SE}
	addl	%d0,%d2		//in d2 as index into RTABLE
	leal	RTABLE,%a1	//load rtable base
	moveb	(%a1,%d2),%d0	//load new rounding bits from table
	clrl	%d3			//clear d3 to force no exc and extended
	bfins	%d0,%d3{#26:#2}	//stuff new rounding bits in FPCR
	fmovel	%d3,%FPCR		//write new FPCR
	asrl	#1,%d0		//write correct PTENxx table
	bccs	not_rp		//to a1
	leal	PTENRP,%a1	//it is RP
	bras	calc_p		//go to init section
not_rp:
	asrl	#1,%d0		//keep checking
	bccs	not_rm
	leal	PTENRM,%a1	//it is RM
	bras	calc_p		//go to init section
not_rm:
	leal	PTENRN,%a1	//it is RN
calc_p:
	movel	%d1,%d0		//copy exp to d0;use d0
	bpls	no_neg		//if exp is negative,
	negl	%d0		//invert it
	orl	#0x40000000,(%a0)	//and set SE bit
no_neg:
	clrl	%d3		//table index
	fmoves	FONE,%fp1	//init fp1 to 1
e_loop:
	asrl	#1,%d0		//shift next bit into carry
	bccs	e_next		//if zero, skip the mul
	fmulx	(%a1,%d3),%fp1	//mul by 10**(d3_bit_no)
e_next:
	addl	#12,%d3		//inc d3 to next rtable entry
	tstl	%d0		//check if d0 is zero
	bnes	e_loop		//not zero, continue shifting
//
//
//  Check the sign of the adjusted exp and make the value in fp0 the
//  same sign. If the exp was pos then multiply fp1*fp0;
//  else divide fp0/fp1.
//
// Register Usage:
//  norm:
//	( )  a0: pointer to working bcd value
//	(*) fp0: mantissa accumulator
//	( ) fp1: scaling factor - 10**(abs(exp))
//
norm:
	btst	#30,(%a0)	//test the sign of the exponent
	beqs	mul		//if clear, go to multiply
div:
	fdivx	%fp1,%fp0		//exp is negative, so divide mant by exp
	bras	end_dec
mul:
	fmulx	%fp1,%fp0		//exp is positive, so multiply by exp
//
//
// Clean up and return with result in fp0.
//
// If the final mul/div in decbin incurred an inex exception,
// it will be inex2, but will be reported as inex1 by get_op.
//
end_dec:
	fmovel	%FPSR,%d0		//get status register	
	bclrl	#inex2_bit+8,%d0	//test for inex2 and clear it
	fmovel	%d0,%FPSR		//return status reg w/o inex2
	beqs	no_exc		//skip this if no exc
	orl	#inx1a_mask,USER_FPSR(%a6) //set inex1/ainex
no_exc:
	moveml	(%a7)+,%d2-%d5
	rts
	|end