Intel 80286, 80287 manual Ebde

NUMERIC PROGRAMMING EXAMPLES

iAPX286 MACRO ASSEMBLER 80287 Floating-Point to 18-Dig.it ASCII Conversion 10: 12: 38 09/25/83 PAGE

LOC	DB..}	LINE
		134
0012		135
		136
0012 EBOODO		137
0015	81308	138
0017	2EBAB70200	139
ODIC	3CFE	140
ODIE	7528	141
		142
		143
		144
0020 C20AOO		145
		146
		147
		148
0023		149
		150
0023	ODDS	151
0025	EB02	152
		153
		154
		155
0027		156
		157
0027	BOFE	158
		159
0029		160
		161
0029	C9	162
002A	07	163
00213	C20AOO	164
		165
		166
		167
002E		168
		169
		170

SOURCE

call	tos_status	Look at status of ST(O)
	b 1, ax	Get	descriptor	frOm table
	a1,status_table[bx]	Look	for empty	STeO)
	OIL INVALID

ST(O) is empty! Return the status value.

RE'move infinity from stack and exit.

fstp	st (0)	;	OK to leave fstp running
Jm,	short	exit_proc
String space is too small! Return invalld code
	OIL INVALID
leave		i	RestorE.' stack
pop	es
ret	parms_size

ST(O) is NAN or indefinite. Store the value in memory and look at the fraction field to separate indefinite from an ordinary NAN.

002E	DI37EFO	171
0031	A801	172
0033	98	173
0034	74F3	174
0086	DBDoeo	175
		17.
0039	285EF6	177
003C	OBSEF4	178
003F	OB5EF2	179
0042	OB5EFO	180
0045	75E2	181
0047	B003	182
		183
0049	EBDE	184
		185

fstp	fraction
test	ai, MINUS
fwait
JZ	exit.JIroc
mov	bx.OCOOOH
sub	bx.word ptr fraction+6
	bx. word	ptr	fraction+4
	bx. word	ptr	fraction+2
or	bx. word	ptr	fraction
Jnz	9xit..JH·OC
	al, INDEFINITE
Jmp	exit.JIroc

Remove value from stack for examination Look at sign bit

Insure stoT'e is done

Can't be indefinite if positive

Match against upper 16 bits· of fraction CompaT'e bits 63-48

Bits 32-47 must be zero Bits,l'31-16 must be zero Bits 15-0 must be zero

Set return value for indefinite value

		18.
		187
0048		188
		189
0048	06	190
		191
004C	eS100aoo	192
0050	884EOB	193
		19'
0053	B3F902	195
0056	7CCF	19.
0058	49	197
		198
0059	83F912	199
Dose	7603	200
DOSE B91200		201
		202
OD61		203
		204
0061	3C06	205
		20.
0063	?DBE	207
0065	3C04	208
		209
0067	7DCS	210
		211
		212
		213

Allocate stack space for local variables and establish parameter addressibility.

not_empty:
push		Save working register
enter	10cal_size.O	FOT'mat stOiC II
	"
mov	cx. field_size	Check for enough string space
<m,	cx.2
Jl	small_string
do<	"c x. BCD_DIGITS	AdJust for sign character
<m,		See if string is too large for BCD
J"	size_ok
	c x. BCD_DIGITS	Else set maximum string size
size_ok:
<m,	aI. INFINITY	Look for infinity
".	found_i nfi n i ty	Return status value for + or - inf,
<m,	al. NAN	Look for NAN or INDEFINITE
JO'	NAN_or _indefinite

Set default return values and check that the number is normalized.

0069 D9El		21.
006B	8800	215
		21.
0060	33CO	217
006F 8B7EOE		218
0072	8905	219
0074	BB5E06	220
0077	8907	221
0079 eOFAFC		222
007C	7828	223
D07E	SOFAFA	22.
		225
0081	732C	226
		227

	dx. ax
mov	ax. ax
	di. denormal.JItr
mov	word ptr [di.:J, ax
	bx. power.JItr
<m,	word ptr [bx]. ax
	dl. ZERO
J.'	real_zero
<m,	dl. DENORMAL
J ••	found_denormal

Use positive value onll,l

sign bit in 011 has true sign of value Save retuT'n value for later

Form a constant Zero denormal count

Zero power of ten value

Test for zero

Skip power code if value is

Look for a denormal value

Handle it specially

Figure 4-6.

Floating-Point to ASCII Conversion Routine (Cont'd.)

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