Spelunking through math.h to try to find understanding

math_spelunk.c

#include<stdio.h>
#include<math.h>

#include <stdint.h>
#include <string.h>

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define for_endian(size) for (int i = 0; i < size; ++i)
#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define for_endian(size) for (int i = size - 1; i >= 0; --i)
#else
#error "Endianness not detected"
#endif

#define printb(value)                                   \
({                                                      \
        typeof(value) _v = value;                       \
        __printb((typeof(_v) *) &_v, sizeof(_v));       \
})

void __printb(void *value, size_t size)
{
        uint8_t byte;
        size_t blen = sizeof(byte) * 8;
        uint8_t bits[blen + 1];

        bits[blen] = '\0';
        for_endian(size) {
                byte = ((uint8_t *) value)[i];
                memset(bits, '0', blen);
                for (int j = 0; byte && j < blen; ++j) {
                        if (byte & 0x80)
                                bits[j] = '1';
                        byte <<= 1;
                }
                printf("%s ", bits);
        }
        printf("\n");
}

int main() {
    printf("Machine info:\n################\n");
    printf("Byte order\n");
    printf("%i\n", __BYTE_ORDER__);
    printf("Big Endian\n");
    printf("%i\n", __ORDER_BIG_ENDIAN__);
    printf("Little Endian\n");
    printf("%i\n", __ORDER_LITTLE_ENDIAN__);
    printf("\n");
    printf("Math.h info:\n################\n");
    printf("M_PI_2\n");
    printf("%0.16f\n", M_PI_2);
    printb(M_PI_2);
    printf("M_2_PI\n");
    printf("%0.16f\n", M_2_PI);
    printb(M_2_PI);
    printf("\n");
}

Tested using GCC 9.1.0 jdoodle.com/a/1UbD