fshow.c

/* Display structure of floating-point numbers */

#include <stdio.h>
#include <stdlib.h>
float strtof(const char *nptr, char **endptr);

#define FLOAT_SIZE 32
#define FRAC_SIZE 23
#define EXP_SIZE 8
#define BIAS ((1 << (EXP_SIZE - 1)) - 1)
#define FRAC_MASK ((1 << FRAC_SIZE) - 1)
#define EXP_MASK ((1 << EXP_SIZE) - 1)

/* Floating point helpers */
unsigned f2u(float f)
{
    union {
        unsigned u;
        float f;
    } v;
    v.u = 0;
    v.f = f;
    return v.u;
}

static float u2f(unsigned u)
{
    union {
        unsigned u;
        float f;
    } v;
    v.u = u;
    return v.f;
}

/* Get exponent */
unsigned get_exp(unsigned uf)
{
    return (uf >> FRAC_SIZE) & EXP_MASK;
}

/* Get fraction */
unsigned get_frac(unsigned uf)
{
    return uf & FRAC_MASK;
}

/* Get sign */
unsigned get_sign(unsigned uf)
{
    return (uf >> (FLOAT_SIZE - 1)) & 0x1;
}

void show_float(unsigned uf)
{
    float f = u2f(uf);
    unsigned exp = get_exp(uf);
    unsigned frac = get_frac(uf);
    unsigned sign = get_sign(uf);

    printf("\nFloating point value %.10g\n", f);
    printf(
        "Bit Representation 0x%.8x, sign = %x, exponent = 0x%.2x, fraction = "
        "0x%.6x\n",
        uf, sign, exp, frac);
    if (exp == EXP_MASK) {
        if (frac == 0) {
            printf("%cInfinity\n", sign ? '-' : '+');
        } else
            printf("Not-A-Number\n");
    } else {
        int denorm = (exp == 0);
        int uexp = denorm ? 1 - BIAS : exp - BIAS;
        int mantissa = denorm ? frac : frac + (1 << FRAC_SIZE);
        float fman = (float) mantissa / (float) (1 << FRAC_SIZE);
        printf("%s.  %c%.10f X 2^(%d)\n",
               denorm ? "Denormalized" : "Normalized", sign ? '-' : '+', fman,
               uexp);
    }
}

/* Extract hex/decimal/or float value from string */
static int get_num_val(char *sval, unsigned *valp)
{
    char *endp;
    /* See if it's an integer or floating point */
    int ishex = 0;
    int isfloat = 0;
    for (int i = 0; sval[i]; i++) {
        switch (sval[i]) {
        case 'x':
        case 'X':
            ishex = 1;
            break;
        case 'e':
        case 'E':
            if (!ishex)
                isfloat = 1;
            break;
        case '.':
            isfloat = 1;
            break;
        default:
            break;
        }
    }
    if (isfloat) {
        float fval = strtof(sval, &endp);
        if (!*endp) {
            *valp = *(unsigned *) &fval;
            return 1;
        }
        return 0;
    } else {
        long long int llval = strtoll(sval, &endp, 0);
        long long int upperbits = llval >> 31;
        /* will give -1 for negative, 0 or 1 for positive */
        if (valp && (upperbits == 0 || upperbits == -1 || upperbits == 1)) {
            *valp = (unsigned) llval;
            return 1;
        }
        return 0;
    }
}

void usage(char *fname)
{
    printf("Usage: %s val1 val2 ...\n", fname);
    printf(
        "Values may be given as hex patterns or as floating point numbers\n");
    exit(0);
}

int main(int argc, char *argv[])
{
    unsigned uf;
    if (argc < 2)
        usage(argv[0]);
    for (int i = 1; i < argc; i++) {
        char *sval = argv[i];
        if (get_num_val(sval, &uf)) {
            show_float(uf);
        } else {
            printf("Invalid 32-bit number: '%s'\n", sval);
            usage(argv[0]);
        }
    }
    return 0;
}