vrs4_logf: Four-valued single precision natural logarithm

• C Prototype:
  • __m128 __vrs4_logf(__m128 x);
  • Inputs:
    • __m128 x - the single precision input values.
  • Outputs:
    • The natural (base e) logarithm of x.
    • __m128 y - the single precision natural logarithm results, returned in xmm0.
• Notes:
  • __vrs4_logf computes the natural 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 natural logarithm of all four values, returned as a __m128 value. This is a relaxed version of logf, 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:
  • 124 cycles for most valid inputs (31 cycles per value).