fastlog2f: fast single precision base-2 logarithm function

• Weak alias: log2f
• C Prototype:
  • float fastlog2f (float x);
  • Inputs:
    • float x - the single precision input value.
  • Outputs:
    • The base-2 logarithm of x.
• Fortran Function Interface:
  • REAL FASTLOG2F(X)
  • Inputs:
    • REAL X - the single precision input value.
  • Return Value:
    • The base-2 logarithm of X.
• Notes:
  • fastlog2f computes the single precision base-2 logarithm of its argument x.
    
    This is a relaxed version of log2f, 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
    +/- 0	-infinity
    negative	QNaN
    QNaN	same QNaN
    SNaN	same NaN converted to QNaN
    +infinity	+infinity
    -infinity	QNaN

• Performance:
  • 107 cycles for most valid inputs.