A c program that will decompose an IEEE-754 Double Precision Floating Point number into its constituent parts. ONLY WORKS ON LITTLE-ENDIAN SYSTEMS.

ieedouble.c

#include <stdint.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
//NOTE: only works on little-endian systems
union dub
{
        double real;
        uint64_t whole;
        uint32_t half[2];
        uint16_t quarter[4];
        uint8_t eighths[8];
};

int main(int argc, char *argv[])
{
        if(argc<2)
        {
                puts("Error: must supply floating point value.");
                exit(1);
        }
        union dub d;
        sscanf(argv[1],"%lf",&d.real);
        printf("Real value:   %f %a\n",d.real,d.real);
        printf("Long value:   %lu\n",d.whole);
        printf("Int values:   %u %u\n",d.half[1],d.half[0]);
        printf("Short values: %u %u %u %u\n",d.quarter[3],d.quarter[2],d.quarter[1],d.quarter[0]);
        printf("Byte values:  %u %u %u %u %u %u %u %u\n",d.eighths[7],d.eighths[6],d.eighths[5],d.eighths[4],d.eighths[3],d.eighths[2],d.eighths[1],d.eighths[0]);
        printf("----------\nParts: sign: %d, ", ((d.eighths[7] & 0x80)/*==0x80*/?1:0));
        int _exp = ((d.eighths[7] & 0x7F) << 4) | ((d.eighths[6] & 0xF0) >> 4);
        printf("expt: %4d (raw %5d minus offset 1023), ", _exp-1023, _exp);
        long long mant;
        mant |=(d.eighths[6]&0x0F); mant <<=8;
        mant |=(d.eighths[5]&0xFF); mant <<=8;
        mant |=(d.eighths[4]&0xFF); mant <<=8;
        mant |=(d.eighths[3]&0xFF); mant <<=8;
        mant |=(d.eighths[2]&0xFF); mant <<=8;
        mant |=(d.eighths[1]&0xFF); mant <<=8;
        mant |=(d.eighths[0]&0xFF);// mant <<=8;
        union dub dd;
        sscanf(argv[1],"%lf",&dd.real);
        dd.whole&=0x000fffffffffffff;
        dd.whole|=(0x3ff0000000000000);
        printf("mant: %f (%lld, 0x%016llX)\n", dd.real, mant, mant);
        printf("Hex: 0x");
        for(int i=7; i>-1; i--)
        {
                printf("%02hhx",d.eighths[i]);
        }
        puts("");
        int qqq=0;
        for(int i=0; i<8; i++)
        {
                printf("%8d",qqq++);
        }
        puts("");
        for(int i=7; i>-1; i--)
        {
                for(int q=7; q>-1; q--)
                {
                        if((i==7 && q==6) || (i==6 && q==3))
                        {
                                printf("\e[3%dm",i-1);
                        }
                        printf("%c",(d.eighths[i]>>q)%2==0?'0':'1');
                }
        }
        printf("\e[0m\n");
        printf("-1^(%d) * 2^(%d) * %f = %f\n",(d.eighths[7]&0x80)>>7,_exp-1023,dd.real,(dd.real * exp2(_exp-1023) * (d.eighths[7]&0x80?-1:1)));
        return 0;
}