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decode_float.c
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decode_float.c
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#include <stdio.h>
void decode_float(float value)
{
const int exponent_bias = 127;
const int mantissa_base = 1 << 23;
const int max_exponent = 255;
const int mantissa_mask = 0x07fffff;
const int mantissa_bits = 23;
const int exponent_bits = 8;
typedef union {
float value;
__uint32_t x;
} IEEE_754_float;
IEEE_754_float f;
f.value = value;
__uint32_t x = f.x;
unsigned int sign = 0x01 & (x >> (mantissa_bits + exponent_bits));
unsigned int exponent = max_exponent & (x >> mantissa_bits);
unsigned int mantissa = mantissa_mask & x;
printf("%+10.4f ", value);
if (exponent == max_exponent) {
if (mantissa == 0) {
printf("%c infinity\n", sign ? '-' : '+');
} else {
puts("NaN");
}
} else {
printf("%c %10.8f x 2^%-2d\n", sign ? '-' : '+',
1.0 + (float) mantissa / mantissa_base, exponent - exponent_bias);
}
}
int main(void)
{
float values[] = {0.0, 0.1, 0.2, 1.0, 2.0, 10.0, 100.0, 1000.0, 1000.1, 1.0/0.0, -0.0, -0.1, -0.2, -1.0, -1000.0, -1.0/0.0, 0.0/0.0};
int i;
for (i=0; i<sizeof(values)/sizeof(float); i++) {
decode_float(values[i]);
}
return 0;
}