Thread: FPN math

Some of you will already know this but I'm working on a function for a compiler I'm making, this function is supposed to read both integers and floating numbers based on text provided. I was struggling to identify what variables I needed where and how to handle them, I then thought to do a small project/file with fixed data to verify those details, thing is I've now hit a roadblock and struggling to come up with ideas of how to fix it, I think my problem lies in how I calculate the mantissa (parameter man) but it could also be the exponent (parametet exp) or both, I started with the floating part as 0 to check the exponent so I don't think it's that though. Here's what I have so far:

Code:

#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <float.h>
typedef unsigned char uchar;
typedef unsigned long long ullong;
#define TYPE float
typedef union LDBL {
	TYPE fpn;
	uchar hex[sizeof(TYPE)];
	struct {
		ulong man : 23;
		ulong exp : 8;
		ulong sig : 1;
	};
} LDBL;

void print( char *text, LDBL val ) {
	printf("%s",text);
	for ( size_t i = 0; i < sizeof(TYPE); ++i ) {
		printf( " %02X", val.hex[i] );
	}
}
#define NUM 2
#define FPN 0
int main() {
	ulong num = 3, fpn = 0, exp = 0;
	ulong bit = 1, pos = 0;
	LDBL test = {0}, mine = {0};
	test.fpn = fpn;
	test.fpn /= 10;
	test.fpn += num;
	printf("%E\n", test.fpn);
	for ( pos = 0; bit; bit <<= 1 ) {
		mine.man |= bit;
		if ( num & bit ) mine.exp = pos;
		++pos;
		if ( pos == FLT_MAX_EXP ) break;
	}
	mine.exp += FLT_MAX_EXP;
	if ( exp )
		mine.exp = (mine.exp == (FLT_MAX_EXP) * 2) ? -1 : mine.exp + exp;
	num *= 10;
	bit = 1;
	pos = 0;
	if ( mine.exp != (FLT_MAX_EXP + exp) )
		for ( ; !(bit & num); bit <<= 1, ++pos );
	for ( ; pos < 23; ++pos ) {
		fpn <<= 1;
		mine.man <<= 1;
		if ( !fpn ) break;
		mine.man |= (fpn & bit);
	}
	print( "test", test );
	putchar('\n');
	print( "mine", mine );
	putchar('\n');
	printf( "%08X %08X\n", test.exp, mine.exp );
	return 0;
}

I'll take a look at some bugs mentioned of mitsy before taking a break until I think of something or someone else manages to think of something (and posts it)

Edit: Oh and here are my results:

Code:

gcc -Wall -o "test_fpn" "test_fpn.c" && "./test_fpn"
3.000000E+00
test 00 00 40 40
mine FE FF FF 40
00000080 00000081
Compilation finished successfully.