m68k/fpsp040/decbin.S

4 |	Description: Converts normalized packed bcd value pointed to by
5 |	register A6 to extended-precision value in FP0.
13 |	Speed: The program decbin takes ??? cycles to execute.
24 |	A1.	Convert the bcd exponent to binary by successive adds and muls.
25 |	Set the sign according to SE. Subtract 16 to compensate
26 |	for the mantissa which is to be interpreted as 17 integer
30 |	A2. Convert the bcd mantissa to binary by successive
31 |	adds and muls in FP0. Set the sign according to SM.
39 |	exponent equal to the exponent from A1 and the zero count
53 |	tables rounded to RN, RM, and RP, according to the table
65 |	word to $0100.  This will signal unimp.sa that an enabled inex1
83 |	to nearest, minus, and plus, respectively.  The tables include
127 |  4. Subtract 16 to compensate for interpreting the mant as all integer digits.
138 |	( )  a0: pointer to working bcd value
139 |	( )  a6: pointer to original bcd value
145 	moveql	#ESTRT,%d3	|counter to pick up digits
156 	addqb	#4,%d3		|advance d3 to the next digit
162 	subl	#16,%d1		|sub to compensate for shift of mant
184 |	( )  a0: pointer to working bcd value
185 |	( )  a6: pointer to original bcd value
191 	moveql	#1,%d1		|word counter, init to 1
200 	faddb	%d0,%fp0		|add digit to sum in fp0
207 	moveql	#FSTRT,%d3	|counter to pick up digits
216 |  then inc d1 (=2) to point to the next long word and reset d3 to 0
217 |  to initialize the digit offset, and set d2 to 7 for the digit count;
220 	addqb	#4,%d3		|advance d3 to the next digit
232 	beq	ap_st_z		|if clear, go to append/strip zeros
239 |  this routine calculates the amount needed to normalize the mantissa
242 |  of this is to reduce the value of the exponent and the possibility
256 |   4. Add the count to the exp.
261 |   any adjustment due to append/strip zeros will drive the resultant
263 |   of 27 or less are exact, there is no need to use this routine to
264 |   attempt to lessen the resultant exponent.
275 |	( )  a0: pointer to working bcd value
280 | First check the absolute value of the exponent to see if this
290 	bne	ap_st_n		|if neg, go to neg side
292 	movel	(%a0),%d4		|load lword 1 to d4
297 	movel	(%a0,%d5.L*4),%d4	|get lword 2 to d4
301 	movel	(%a0,%d5.L*4),%d4	|get lword 3 to d4
307 	bnes	ap_p_fx		|if non-zero, go to fix exp
308 	addql	#4,%d3		|point to next digit
312 	movel	%d1,%d0		|copy counter to d2
315 	bges	ap_p_fm		|if still pos, go to pwrten
317 	movel	(%a0),%d4		|load lword 1 to d4
321 | Calculate the mantissa multiplier to compensate for the striping of
327 	fmoves	FONE,%fp1	|init fp1 to 1
328 	moveql	#3,%d2		|init d2 to count bits in counter
334 	addl	#12,%d3		|inc d3 to next rtable entry
344 	moveql	#2,%d5		|set up d5 to point to lword 3
347 	subl	#1,%d5		|dec d5 to point to lword 2
351 	movel	#28,%d3		|point to last digit
355 	bnes	ap_n_fx		|if non-zero, go to exp fix
356 	subql	#4,%d3		|point to previous digit
360 	movel	%d1,%d0		|copy counter to d0
365 	movel	(%a0),%d4		|load lword 1 to d4
369 | Calculate the mantissa multiplier to compensate for the appending of
370 | zeros to the mantissa.
375 	fmoves	FONE,%fp1	|init fp1 to 1
376 	moveql	#3,%d2		|init d2 to count bits in counter
382 	addl	#12,%d3		|inc d3 to next rtable entry
403 |	( )  a0: pointer to working copy of bcd
408 | according to the following table:
433 	movel	(%a0),%d4		|reload 1st bcd word to d4
434 	asll	#2,%d2		|format d2 to be
439 	clrl	%d3			|clear d3 to force no exc and extended
443 	bccs	not_rp		|to a1
445 	bras	calc_p		|go to init section
450 	bras	calc_p		|go to init section
454 	movel	%d1,%d0		|copy exp to d0;use d0
460 	fmoves	FONE,%fp1	|init fp1 to 1
466 	addl	#12,%d3		|inc d3 to next rtable entry
477 |	( )  a0: pointer to working bcd value
483 	beqs	mul		|if clear, go to multiply