decbin.s

VXWORKS源代码

|  if the exp was positive, and added if it was negative.  The purpose
|  of this is to reduce the value of the exponent and the possibility
|  of error in calculation of __x_pwrten.
|
|  1. Branch on the sign of the adjusted exponent.
|  2p.(positive exp)
|   2. Check M16 and the digits in lwords 2 and 3 in decending order.
|   3. Add one for each zero encountered until a non-zero digit.
|   4. Subtract the count from the exp.
|   5. Check if the exp has crossed zero in #3 above|  make the exp abs
|	   and set SE.
|	6. Multiply the mantissa by 10**count.
|  2n.(negative exp)
|   2. Check the digits in lwords 3 and 2 in decending 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 resultane
|   exponent towards zero.  Since all __x_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:
|
|  __x_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.
|
__x_ap_st_z:
	movel	a6@(L_SCR1),d1	| load expA for range test
	cmpl	#27,d1		| test is with 27
	jle 	__x_pwrten	| if abs(expA) <28, skip ap/st zeros
	btst	#30,a0@		| check sign of exp
	jne 	__x_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
	jne 	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
	jne 	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
	jne 	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	a6@(L_SCR1),d1	| get adjusted exp from memory
	subl	d0,d1		| subtract count from exp
	jge 	ap_p_fm		| if still pos, go to __x_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	#__x_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
	jcc 	ap_p_en		| if 1, mul fp1 by __x_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
	jne 	ap_p_el		| if not, get next bit
	fmulx	fp1,fp0		| mul mantissa by 10**(no_bits_shifted)
	jra 	__x_pwrten		| go calc __x_pwrten
|
| This section handles a negative adjusted exponent.
|
__x_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
	jne 	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
	jne 	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	a6@(L_SCR1),d1	| get adjusted exp from memory
	subl	d0,d1		| subtract count from exp
	jgt 	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	#__x_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
	jcc 	ap_n_en		| if 1, mul fp1 by __x_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
	jne 	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:
|
|  __x_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
|
|
__x_pwrten:
	movel	a6@(USER_FPCR),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
	lea	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
	jcc 	not_rp		| to a1
	lea	__x_PTENRP,a1	| it is RP
	jra 	calc_p		| go to init section
not_rp:
	asrl	#1,d0		| keep checking
	jcc 	not_rm
	lea	__x_PTENRM,a1	| it is RM
	jra 	calc_p		| go to init section
not_rm:
	lea	__x_PTENRN,a1	| it is RN
calc_p:
	movel	d1,d0		| copy exp to d0| use d0
	jpl 	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
	jcc 	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
	jne 	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:
|  __x_norm:
|	( )  a0: pointer to working bcd value
|	(*) fp0: mantissa accumulator
|	( ) fp1: scaling factor - 10**(abs(exp))
|
__x_norm:
	btst	#30,a0@		| test the sign of the exponent
	jeq 	mul		| if clear, go to multiply
div:
	fdivx	fp1,fp0		| exp is negative, so divide mant by exp
	jra 	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 __x_decbin incurred an inex exception,
| it will be inex2, but will be reported as inex1 by __x_get_op.
|
end_dec:
	fmovel	FPSR,d0			| get status register
	bclr	#__x_inex2_bit+8,d0	| test for inex2 and clear it
	fmovel	d0,FPSR			| return status reg w/o inex2
	jeq 	no_exc			| skip this if no exc
	orl	#inx1a_mask,a6@(USER_FPSR) | set inex1/ainex
no_exc:
	moveml	a7@+,d2-d5
	rts
|	end