/*
   Name:    hw15.c
   Purpose: Illustrates use of bit-fields and unions to observe floating point
            representation.
   Author:  Bill Slough
 */

#include <stdio.h>

void display_float(unsigned int sign, unsigned int exponent, unsigned int fraction);
void display_hex(float value);
void demo_display_float(void);
void demo_display_hex(void);

/* IEEE 754 single precision floating point type */
struct float_t {
    unsigned int fraction: 23;   /* 23-bit mantissa */
    unsigned int exponent: 8;    /* exponent, excess-127 */
    unsigned int sign: 1;        /* sign bit: 0 = +   1 = - */
};

union float_view {           /* three ways to view a floating point value: */
    float f;                 /* ... as a float */
    struct float_t IEEE;     /* or three fields, per IEEE */
    unsigned int x;          /* or 32 bits */
};

int main(void) {
    /* show each type of conversion */
    demo_display_float();
    demo_display_hex();

    return 0;
}

/* Given the three components of a single precision floating point value,
   display it in base 10, "human readable" form */
void
display_float(unsigned int sign, unsigned int exponent, unsigned int fraction) {
    union float_view view;

    view.IEEE.sign = sign;
    view.IEEE.exponent = exponent;
    view.IEEE.fraction = fraction;

    printf("Floating point value = %12.8f\n", view.f);
}

/* Display a single precision floating point value as a hexadecimal value */
void
display_hex(float value) {
    union float_view view;

    view.f = value;
    printf("sign = %1d, expo = 0x%2.2x, fraction = 0x%6.6x (0x%8.8x)\n",
           view.IEEE.sign,
           view.IEEE.exponent,
           view.IEEE.fraction,
           view.x);
}

void demo_display_float(void) {
    int n;
    int i;
    unsigned int sign, exponent, fraction;

    printf("Demo #1:  sign:exponent:fraction -> floating point value\n");
    printf("  sign    : 0 or 1\n");
    printf("  exponent: 2 digit hexadecimal value\n");
    printf("  fraction: 6 digit hexadecimal value (0x000000 ... 0x7FFFFF)\n\n");

    printf("Enter desired number of test cases: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++) {
        printf("> ");
        scanf("%x:%x:%x", &sign, &exponent, &fraction);
        display_float(sign, exponent, fraction);
        printf("\n");
    }
    printf("\n");
}

void demo_display_hex(void) {
    int i;
    int n;
    float value;

    printf("Demo #2:  floating point value -> hexadecimal representation \n");

    printf("Enter desired number of test cases: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++) {
        printf("> ");
        scanf("%f", &value);
        display_hex(value);
        printf("\n");
    }
    printf("\n");
}