log1pf Function

Calculates the natural logarithm of a single precision floating-point value plus 1.

Include

<math.h>

Prototype

float log1pf(float x);

Argument

x

any positive value for which to return the log

Return Value

Returns the natural logarithm of x+1. The result of log1pf(x) is generally expected to be more accurate than that of logf(x+1) when the magnitude of x is small.

Remarks

A domain error occurs if x is less than 1. A range error might occur if the argument equals 1.

Example

#include <math.h>
#include <stdio.h>
#include <errno.h>

int main(void)
{
  float x, y;

  errno = 0;
  x = 2.0;
  y = log1pf(x);
  if(errno)
    perror("Error");
  printf("The result of log1pf(%f) is %f\n", x, y);

  errno = 0;
  x = 0.0;
  y = log1pf(x);
  if(errno)
    perror("Error");
  printf("The result of log1pf(%f) is %f\n", x, y);

  errno = 0;
  x = -2.0;
  y = log1pf(x);
  if(errno)
    perror("Error");
  printf("The result of log1pf(%f) is %f\n", x, y);
}

Example Output

The result of log1pf(2.000000) is 1.098612
The result of log1pf(0.000000) is 0.000000
Error: domain error
The result of log1pf(-2.000000) is nan