Visualizing and understanding IEEE 754 floating point values

floating.c

//
//  floating.c
//  funbits
//
//  Created by Leptos on 8/18/18.
//  Copyright © 2018 Leptos. All rights reserved.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>

#define printBitRepresentationBuff(a)                         \
    ({                                                        \
        size_t _i = sizeof(a) * CHAR_BIT;                     \
        char _buff[_i + 1];                                   \
        char *_buff_p = _buff;                                \
        for (; _i; _i--) {                                    \
            *(_buff_p++) = (a & (1 << (_i - 1))) ? '1' : '0'; \
        }                                                     \
        *_buff_p = '\0';                                      \
        puts(_buff);                                          \
    })

int main() {
    union {
        float floating;
        uint32_t decimal;
        struct {
            uint32_t mantissa : 23;
            uint16_t exponent : 8;
            uint8_t sign : 1;
        } ieee;
    } single_ex;
    _Static_assert(sizeof(single_ex) == sizeof(float), "Expecting struct size to match main type size");
    _Static_assert(sizeof(single_ex.decimal) == sizeof(single_ex.floating), "Expecting main type size to match representing size");
    _Static_assert(sizeof(single_ex.decimal) == sizeof(single_ex.ieee), "Expecting main type size to match expanded form size");
    
    puts("Single precision");
    single_ex.floating = 0.15625;
    printBitRepresentationBuff(single_ex.decimal);
    printf("%+f\n", single_ex.floating);
    single_ex.ieee.sign = 1;
    printf("%+f\n", single_ex.floating);
    
    union {
        double floating;
        uint64_t decimal;
        struct {
            uint64_t mantissa : 52;
            uint16_t exponent : 11;
            uint8_t sign : 1;
        } ieee;
    } double_ex;
    _Static_assert(sizeof(double_ex) == sizeof(double), "Expecting struct size to match main type size");
    _Static_assert(sizeof(double_ex.decimal) == sizeof(double_ex.floating), "Expecting main type size to match representing size");
    _Static_assert(sizeof(double_ex.decimal) == sizeof(double_ex.ieee), "Expecting main type size to match expanded form size");
    
    puts("Double precision");
    double_ex.floating = 0.15625;
    printBitRepresentationBuff(double_ex.decimal);
    printf("%+f\n", double_ex.floating);
    double_ex.ieee.sign = 1;
    printf("%+f\n", double_ex.floating);
}