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    Floating Point Package for BDS C
    ********************************
    Written by: Bob Mathias
    this doc by: Leor Zolman

	Components of the floating point package:

    1)	FLOAT.DOC:	This documentation file
    2)	FLOAT.C:	File of support functions, written in C
    3)	FP:		The workhorse function (in DEFF2.CRL)
    4)  FLOATSUM.C	A Sample use of all this stuff

	Here's how it works: for every floating point number
you wish to work with, you must declare a five (5) element
character array. Then, pass a pointer to the array whenever
you need to specify it in a function call. Each of Bob's
functions expects its arguments to be pointers to such 
character arrays.

	The four basic arithmetic functions are: fpadd,
fpsub, fpmul and fpdiv. They each take three arguments: a
pointer to a five character array where the result will go,
and the two operands (each a pointer to a five character array
representing a floating point operand.)

NOTE THAT THE RESULT MAY BE PLACED INTO EITHER OF THE ARGUEMENTS
WITH NO ILL EFFECTS. I.e., the operation:
	 fpmult(foo,foo,foo);
will successfully square 'foo' and place the result in 'foo'.

	To initialize the floating point character arrays to the
values you desire and print out the values in a human-readable form,
the following functions are included:

	ftoa: converts a floating point number to an ASCII
	      string (which you can then print out with "puts")
	      NOTE: explicit use of this function has been made
		    obsolete by the new "sprintf." See FLOAT.C.

	atof: converts an ASCII string (null terminated) to
	      a floating point number

	itof: converts integer to floating point.

Here are Bob's descriptions of the functions:

		-----------------------------------

The following functions allow BDS C compiler users to access
and manipulate real numbers. Each real number must be allocated
a five (5) byte character array (char fpnoÆ5Å).  The first four
bytes contain the mantissa with the first byte being the least
significant byte.  The fifth byte is the exponent.

fpcomp(op1,op2)
char op1Æ5Å,op2Æ5Å;
			Returns:
			an integer 1 if op1 > op2
			an integer -1 if op1 < op2
			a zero if op1 = op2
		As with most floating point packages, it is not
		a good practice to compare for equality when
		dealing with floating point numbers.

char *fpadd(result,op1,op2)
char resultÆ5Å, op1Æ5Å, op2Æ5Å;
		Stores the result of op1 + op2 in result. op1
		and op2 must be floating point numbers.
		Returns a pointer to the beginning of result.


char *fpsub(result,op1,op2)
char resultÆ5Å,op1Æ5Å,op2Æ5Å;
		Stores the result of op1 - op2 in result.  op1
		and op2 must be floating point numbers.  
		Returns a pointer to the beginning of result.

char *fpmult(result,op1,op2)
char resultÆ5Å,op1Æ5Å,op2Æ5Å;
		Stores the result of op1 * op2 in result.  op1
		and op2 must be floating point numbers. Returns
		a pointer to the beginning of result.

char *fpdiv(result,op1,op2)
char resultÆ5Å,op1Æ5Å,op2Æ5Å;
		Stores the result of op1 / op2 in result.  op1
		and op2 must be floating point numbers.  
		A divide by zero will return zero as result.
		Returns a pointer to the beginning of result.

char *atof(op1,s1)
char op1Æ5Å,*s;
		Converts the ASCII string s1 into a floating
		point number and stores the result in op1.  
		The function will ignore leading white space 
		but NO white space is allowed to be embedded
		withing the number. The following are legal
		examples:
		"2", "22022222222383.333", "2.71828e-9",
		"334.3333E32".
		"3443.33 E10" would be ILLEGAL because
		it contains an embedded space.
		The value of the exponent must be within the
		range: -38 <= exponent <= 38.
		A pointer to the result is returned.

char *ftoa(s1,op1)
char *s1,op1Æ5Å;
		Converts the floating point number op1 to an 
		ASCII string.  It will be formatted in 
		scientific notation with seven (7) digits of
		precision. The string will be terminated by
		a null.
		Returns a pointer to the beginning of s1.

char *itof(op1, n)
char op1Æ5Å;
int n;
		Sets the floating pt. number op1 to the value
		of integer n. n is assumed to be a SIGNED
		integer.


General observations:

	Because floating point operations must be thought of
in terms of FUNCTION CALLS rather than simple in-line
expressions, special care must be taken not to confuse the
abilities of the compiler with the abilities of the floating
point package. To give a floating point number an initail
value, for instance, you cannot say:

	char fpnoÆ5Å;
	fpno = "2.236";

To achieve the desired result, you'd have to say:	

	char fpnoÆ5Å;
	atof(fpno,"2.236");

Moreover, let's say you want to set a floating point number
to the value of an integer variable called "ival". Saying:

	char fpnoÆ5Å;
	int ival;
	...
	fpno = ival;

will not work; you have to change that last line to:

	itof(fpno,ival);

	Some more examples:

	The following will add 100.2 & -7.99 and store the
	result at the five character array location 'a':
		fpadd(a,atof(b,"100.2"), atof(c,"-7.99"));
	(note that "b" and "c" must also be five character
	arrays)

	The following would NOT add 1 to 'a' as both op1 and 
	op2 must be floating point numbers (actually pointers
	to characters...):

		fpadd(a,a,1);  /* bad use of "fpadd" */

	Thus, it can get a bit hairy when all floating
point numbers are really character arrays; but still, it's
better than nothing.

	All of the above functions are written in C, but
most of them call a single workhorse function called "fp"
to do all the really hairy work. This function has been placed
into the DEFF2.CRL; it is the only machine-coded part of the
package.
«eof»
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