2.92 Float Negate
★★
Problem:
Following the bit-level floating-point coding rules, implement the function with the following prototype:
/* Compute -f. If f is NaN, then return f. */
float_bits float_negate(float_bits f);
For floating-point number f, this function computes -f. If f is NaN, your function should simply return f.
Test your function by evaluating it for all 2^32 values of argument f and comparing the result to what would be obtained using your machine's floating-point operations.
Code:
#include <stdio.h>
#include <assert.h>
typedef unsigned float_bits;
float_bits float_negate(float_bits f) {
unsigned sign = f >> 31;
unsigned exp = f >> 23 & 0xFF;
unsigned frac = f & 0x7FFFFF;
int is_nan = (exp == 0xFF) && (frac != 0);
if (is_nan) {
return f;
}
return (~sign << 31) | (exp << 23) | frac;
}
int main() {
assert(float_negate(0x89)==0x80000089);
assert(float_negate(0x89999999)==0x9999999);
assert(float_negate(0x7F900000)==0x7F900000);
return 0;
}
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