### _fptan -- Calculate Tangent

Format

>     #include <builtin.h>
>     double _fptan(double x);

Language Level: Extension
_fptan calculates the tangent of x, where is x expressed in radians. The value of x must be less than 2**63. This function causes the compiler to emit the appropriate 80387 instruction for the calculation of tangent.

Because it is a built-in function and has no backing code in the library:

- You cannot take the address of _fptan.
- You cannot parenthesize a _fptan function call, because parentheses specify a call to the backing code for the function in the library.

Return Value
_fptan returns the tangent of x expressed in radians.

Example
This example calculates the tangent of PI/4.

    #include <builtin.h>
    #include <stdio.h>

    int main(void)
    {
       double pi;

       pi = 3.1415926;
       printf("The tangent of %lf is %lf.\n", pi/4.0, _fptan(pi/4.0));
       return 0;

       /***************************************************************
          The output should be:

          The tangent of 0.785398 is 1.000000.
       ***************************************************************/
    }

atan - atan2 -- Calculate Arctangent
_fpatan -- Calculate Arctangent
tan -- Calculate Tangent
tanh -- Calculate Hyperbolic Tangent
<builtin.h>