vrs4_log2f: Four-valued single precision base-2 logarithm

• Prototype:
  • __m128 __vrs4_log2f(__m128 x);

  • Inputs:
    • __m128 x - the four single precision inputs.
  • Outputs:
    • The base-2 logarithm of x.
    • __m128 y - the four single precision base-2 logarithm results, returned in xmm0.
• Notes:
  • __vrs4_log2f computes the base-2 logarithm for each of four input arguments.
    
    This routine accepts four single precision input values passed as a __m128 value. The result is the single precision base-2 logarithm of the four values, returned as a __m128 value. This is a relaxed version of log2, suitable for use with fastmath compiler flags or applications not requiring full error handling. Denormal inputs may produce unpredictable results. Special case 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:
  • 141 cycles for most valid inputs (35 cycles per value), longer for input values very close to 1.0.