NJUPT-CSAPP/datalab-handout/fshow.c
2024-06-12 07:36:23 +08:00

151 lines
2.9 KiB
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;
int i;
for (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[])
{
int i;
unsigned uf;
if (argc < 2)
usage(argv[0]);
for (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;
}