decbin.s

MIZI Research, Inc.发布的嵌入式Linux内核源码

|   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