vrd2_log2: Two-valued double precision base-2 logarithm

• C Prototype:
  • __m128d __vrd2_log2(__m128d x);
  • Inputs:
    • __m128d x - the double precision input value pair.
  • Outputs:
    • The base-2 logarithm of x.
    • __m128d y - the double precision base-2 logarithm result pair, returned in xmm0.
• Notes:
  • __vrd2_log2 computes the base-2 logarithm for each of two input arguments.
    
    This routine accepts a pair of double precision input values passed as a __m128d value. The result is the double precision base-2 logarithm of both values, returned as a __m128d 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:
  • 142 cycles for most valid inputs (71 cycles per value), longer for input values very close to 1.0.