fastexp: fast double precision exponential function

• Weak alias: exp
• C Prototype:
  • double fastexp (double x);
  • Inputs:
    • double x - the double precision input value.
  • Outputs:
    • e raised to the power x (exponential of x).
• Fortran Function Interface:
  • DOUBLE PRECISION FASTEXP(X)
  • Inputs:
    • DOUBLE PRECISION X - the double precision input value.
  • Return Value:
    • e raised to the power X (exponential of X).
• Notes:
  • fastexp computes the double precision exponential function of the input argument x.
    
    This is a relaxed version of exp, suitable for use with fastmath compiler flags or applications not requiring full error handling. Denormal inputs may produce unpredictable results. Error inputs produce C99 return values. The routine is accurate to better than 1 ulp over the valid input range.
• Special case return values:

  • Input	Output
    QNaN	same QNaN
    SNaN	same NaN converted to QNaN
    < -708.5	0
    > 709.8	+infinity

• Performance:
  • 75 cycles for most valid inputs.