In C, ldexp() returns x multiplied by 2 raised to exp. ldexp(1.5, 3) is 12, because 1.5 × 2³ is 12.
You pass a double and an int power. Both are required. The result is a double. Include <math.h>.
Pass the number, then the integer power of two. Start with this call.
ldexp(1.5, 3);| Call | What it does |
|---|---|
ldexp(1.5, 3) | Returns 12, which is 1.5 × 8. |
Include <math.h>. On GCC, link with -lm. exp is an int, not a double.
double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);| Parameter | Description |
|---|---|
| x | Required. The double to scale. |
| exp | Required. The int power of two. It can be negative. |
| Return Value | Description |
|---|---|
| Scaled double | x × 2^exp. |
Multiply 5.25 by 2³.
#include <stdio.h>
#include <math.h>
int main(void) {
printf("%.1f\n", ldexp(5.25, 3));
return 0;
}ldexp.5.25 × 8 = 42.%.1f shows one decimal place.A negative exp divides by a power of two.
#include <stdio.h>
#include <math.h>
int main(void) {
printf("%.1f\n", ldexp(8.0, -2));
printf("%.1f\n", ldexp(8.0, -1));
return 0;
}2² = 4 → 8 / 4 = 2.4.0.exp chooses multiply vs divide./ 2.0 loops by hand.frexpSplit with frexp, then rebuild with ldexp.
#include <stdio.h>
#include <math.h>
int main(void) {
int exp;
double x = 42.0;
double frac = frexp(x, &exp);
double back = ldexp(frac, exp);
printf("frac=%.6f exp=%d\n", frac, exp);
printf("back=%.1f\n", back);
return 0;
}frexp(42, &exp) yields mantissa ≈ 0.65625 and exp = 6.ldexp(frac, 6) multiplies by 2⁶ = 64.42.0.Compute the natural logarithm of a positive floating value.
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