Standards
Standards / Extensions |
C or C++ |
Dependencies |
XPG4.2
C99
Single UNIX Specification, Version 3
C++ TR1 C99
|
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
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.