User's Manual

iAPX2B6 MACRO ASSEMBLER
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NUMERIC PROGRAMMING EXAMPLES
80287 Floating-Point to IS-Digit ASCII Conversion
10: 12: 89 09/25/83 PAGE
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SOURCE
fxtratt
cmp dl,UNNDRMAL
Jb normal_value
sub d 1, UNNORMAL-NORMAL
Normalize the fraction.
the denormal count value.
Assert: 0 <'" ST(O) ( 1.0
-Fld 1
J Separate exponent f'T'om significand
, Test for unnormal value
Return normal status with correct Sign
adJust the power of two in ST(1) and 1t.et
,
Load constant to normalize fraction
norma 1 i z e_frac t ion:
fadd st(1).1t.t
hub
f xc h
fi1t.t word ptr CdiJ
faddp st (2). st
ne-g word ph CdiJ
Jnz not_psuedo_zero
Set integer bit in fraction
j Form normalized fraction in ST(O)
J Power of two Held will be negative
of denormal count
j Put denormal count in ST(O)
J Put negative of dl!'normal count in memorl,l
Form correct power of two in stt!)
OK to use word ptr CdiJ now
Form positive denormt!ll count
A psuedo zero will appear an unnormal numbeor. When attemptinll
to normalia it. the resultant fraction field will be zero. Perfo~minll
an f'xtrBct on zero will yield a zero exponent value. .
f~ch ) Put power of tllJO value in !OttO)
Fistp word ptr CdiJ Set denorm<ll count to power of' two value
Word ph (diJ is not u!;ed by convert
integer. OK to letJve running
!:tub dl, NDRMAL-P5UEDO_ZERD ,Set return value saving thf! sign bit
Jmp convert_i.nteger ) Put zero value into memory
The number is a real zero. 'iet the return value and setup for
conversion to BCD
d 1, ZERO-NORMAL
convert_integer
, Convert <;t.3tlIS to normal v<'Jlu!'
i Treat the: l~ro as an i.ntE!geT'
Th. nUmbllr is a dllnoTmal. FXTRACT will not wOTk correctly in tht.
elutt. To corrttetlu slIparate the eKponllnt and fraction, add a fixed
J constant to tht' exponent to guarantee thll rellult il not a denormal.
,
found_d enorma 1:
,
fld 1
heh
fpram
htract
j PTeparl! to. bump axponent
ForeD denormal to smallelit represllntable
utendlld raal -Format exponent
) This will work corrllctly now
The power of the original dllnoT'mal valu. n.n baen safely isohtad.
Check if the fraction value is an unnormal.
ham
htsw
hch
heh
"b
t!!!!t
J'
fstp
atC:!)
dl. DENORMAL-NORMAI..
8K,4400H
norma 1 i :re_fTac t i on
stCO)
SII' if the fraction is an unnormal
Save 80287 statu. In CPU AX rIg for later
I Put uponent in 9T(O)
, Put 1. ~ into SHO), uponant in 9T(2)
j Return normal status with correct lign
j See if! C:3-C:!"O imp ling unnormal aT' NAN
j Jump if -Fraction is an unnormal
j Remov. unnecessary 1. 0 from lIteO)
Calculatt the d.eimal magnitude a"oelated with this numb Ill' to
lIIithin one order. Tnt. error lIIi1l allllays bll inevihbh due to
rounding and lost pr.ttlion. A. a rlSult, we will delibarfttwly fail
to considar the LOOIO of the fraction valua in calculating thll oT'dn.
Since th hattion will alwaYI be 1 <- F <:!, its L.DOIO will not change
thll baSic accurilcl/ oft the function. To get thll decimal order of magnitude.
limply multipl1J tha power of two bl,l L.OQ10(2) and truncate thll ruult to
.an integar.
normal_valu.:
notJlIu.do_:rero:
fltp fTacUon
fiat POWtT'_two
Udlg2
fmul
fhtp power_tan
tlsve ,;;nll Tr.1;;~I.I;U' ii..""; ; ... , ~ ........
Save power of two
Qet L.OQ10(2)
Pow.r_two is noUl saf. to us.
I Form LOG10(of exponent of number)
j AnI,! rounding moda will work harll
Check if the magnitude of thll number rule. out treating it al
integllr.
CX ha. the maximum number of decimal digits allowed.
Figure 4-6. Floating-Point to ASCII Conversion Routine (Cont'd.)
4-10