log1p(), log1pf(), log1pl() — Natural log of x+1
Standards
Standards / Extensions | C or C++ | Dependencies |
---|---|---|
XPG4.2 |
both |
Format
#define _XOPEN_SOURCE_EXTENDED 1
#include <math.h>
double log1p(double x);
C99:
#define _ISOC99_SOURCE
#include <math.h>
float log1pf(float x);
long double log1pl(long double x);
C++
TR1 C99:
#define _TR1_C99
#include <math.h>
float log1p(float x);
long double log1p(long double x);
General description
Computes
The value of x must be greater than -1.0.
Note: The
following table shows the viable formats for these functions. See IEEE binary floating-point for more information about IEEE
Binary Floating-Point.
Function | Hex | IEEE |
---|---|---|
log1p | X | X |
log1pf | X | X |
log1pl | X | X |
Returned value
If successful, log1p() returns the value of the above function of x.
log1p()
will fail under the following conditions:
- If x is less than -1.0, log1p() will return -HUGE_VAL and set errno to EDOM.
- If x is equal to -1.0, log1p() will return -HUGE_VAL and set errno to ERANGE.
Special behavior for IEEE: If successful, log1p()
returns the
The value of x must be greater than -1.0.
log1p() will fail under the following conditions:
- If x is less than -1.0, log1p() will return NaNQ and set errno to EDOM.
- If x is equal to -1.0, log1p() will return -HUGE_VAL and errno remains unchanged.
Note: When environment variable _EDC_SUSV3 is set
to 2, and if x is equal to -1.0, the function
returns -HUGE_VAL and sets errno to ERANGE.