Intel 80286, 80287 manual FLOATING-POINT to Ascii Conversion Examples

NUMERIC PROGRAMMING EXAMPLES

FLOATING-POINT TO ASCII CONVERSION EXAMPLES

Numeric programs must typically format their results at some point for presentation and inspection by the program user. In many cases, numeric results are formatted as ASCII strings for printing or display. This example shows how floating-.point values can be converted to decimal ASCII character strings. The function shown in figure 4-6 can be invoked from PL/M-286, Pascal-286, FORTRAN-286, or ASM2lS6 routines.

Shortness, speed, and accuracy were chosen rather than providing the maximum number of significant digits possible. An attempt is made to keep integers in their own domain to avoid unnecessary conver- sion errors.

Using the extended precision real number format, this. routine achieves a worst case accuracy of three units in the 16th decimal position for a noninteger value or integers greater than 10'8 • This is double precision accuracy. With values having decimal exponents less than 100 in magnitude, the accuracy is one unit in the 17th decimal position.

Higher precision can be achieved with greater care in programming, larger program size, and lower performance.

iAPX2B6 MACRO ASSEMBLER	80287 Floating-Point to	18-Digit ASCII Conversion	10: 12: 38 09/25/83 PAGE
SERIES-III iAPX286 MACRO ASSEMBLER XIC8 ASSEMBLY OF MODULE FLOATING TO ASCII
ODJECT MODULE PLACED IN	: F3: FPASC. DBJ	- -
ASSEMBLER INVOKED BY:	ASM286.86: F3: FPASC. AP2

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$title("B0287 Floating-Point to lS-Digit ASCII Conversion")

public floatin9_to_8Scii

.. xtrn get-pollllll' 10: neaT'.tos_st.tus: near

This subroutine will t'onvert the floating poiflt numbeT' in tne top of the 80287 "tack to <IiIn ASCII string and sepiilrate power oP 10

,,:aling value (in binaf'':!). The maximum width of the ASCII string

POf'med is. controlled by a paf'smeter IIIhich must be :> 1. Unnof'mal values. denormal values. and psuedo zeroes will be correctl.., converted.

A returnli!d value lIIill indicate hOIll many bin"r.., bits 0'

precision "'aT'e lost in an unnormal OT' denormal value. The Iftagnituda (in terms of binary pOlliaf') of iii psuedo zero will al.o be indicated. Integers les. than 10.... 18 in magnitude are accuratell,! converted if the

dntinstion ASCII string 'ield is wide enough to hold all the

digits. Otherlllis.e the valull' i5 converted to scientific notation.

The status of the convlI'T'sion is identified bl,! the retUT'n value. it can be:

oconversion complete. string_size is defined

1invalid arguments

2exact integer conversion. !ltring_size is defined

3indehnite

4+ NAN (Not A Number)

5- NAN

6+ InfinitlJ

7- lnfinit..,

8psuedo zero found, string_size is defined

The PLM/286 calling convention is:

Iloating_to_asc ii:

procedure (number. denormalJltr, stT'ingJltr, sizeJltr. field_5iH" power Jltr) lUord external;

dec: lare (d anormalJl tr. stringJl tr. power Jltr . s i z eJltr) poi nter; declare field_Size word, string_size based sizeJltr wordi declare number reali

declare denoT'mal integar based denormal_ptri declare power integer basad power_ptT'i

and 'loatin9_to_asc i ii

The floating point value is expected to bll' on the top of tha NP)C

.tack. This .ubroutini' •• 0'"peets 3 free ent1'ies on the NP)c stack and

!d~ll pop the passed value when done. The geneT'ated ASCII stT'ing lull have a leading character eitha1' ' - ' or '+'indicilting the sign

of the value. Ttle ASCII decimal digits liJill immediately Pollolil. The numeric viillue of the ASCII string is (ASCII STRINQ. )*10**POWER.

Figure 4-6. Floating-Point to ASCII Conversion Routine

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