log1p, log1pf, log1pl

Artykuł
06/05/2017

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at log1p, log1pf, log1pl2.

Computes the natural logarithm of 1 plus the specified value.

Syntax

double log1p(  
   double x  
);  
  
float log1p(  
   float x  
); //C++ only  
  
long double log1p(  
   long double x  
); //C++ only  
  
float log1pf(  
   float x  
);  
  
long double log1pl(  
   long double x  
);

Parameters

x
The floating-point argument.

Return Value

If successful, returns the natural (base-e) log of (x+1).

Otherwise, may return one of the following values:

Input	Result	SEH exception	errno
+inf	+inf
Denormals	Same as input	UNDERFLOW
±0	Same as input
-1	-inf	DIVBYZERO	ERANGE
< -1	nan	INVALID	EDOM
-inf	nan	INVALID	EDOM
±SNaN	Same as input	INVALID
±QNaN, indefinite	Same as input

The errno value is set to ERANGE if x = -1. The errno value is set to EDOM if x < −1.

Remarks

The log1p functions may be more accurate than using log(x+1) when x is near 0.

Because C++ allows overloading, you can call overloads of log1p that take and return float and long double types. In a C program, log1p always takes and returns a double.

If x is a natural number, this function returns the logarithm of the factorial of (x-1).

Requirements

Function	C header	C++ header
`log1p`, `log1pf`, `log1pl`	<math.h>	<cmath>

For additional compatibility information, see Compatibility.

Udostępnij za pośrednictwem