vrs4_powf: Four-valued single precision power function

• C Prototype:
  • __m128 __vrs4_powf(__m128 x,__m128 y);
  • Inputs:
    • __m128 x - the single precision input base values.
      __m128 y - the single precision input exponent values.
  • Outputs:
    • __m128 z - the single precision results of each x raised to the y power, returned in xmm0.
• Notes:
  • __vrs4_powf() computes the single precision x raised to the y power for four pairs of input arguments. This routine accepts four single precision input value pairs passed as __m128 values. The result is the x raised to the y power for all four input pairs, returned as a __m128 value.
    This is a relaxed version of powf, 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 0.5 ulp over the valid input range.
• Special case return values:

  • Input x	Input y	Output
    +/- 0	y<0, odd integer	+/- infinity
    +/- 0	y<0, not odd integer	+infinity
    +/- 0	y>0, odd integer	+/- 0
    +/- 0	y>0, not odd integer	+0
    -1	+infinity	1
    +1	y (incl. NaN)	1
    x (incl. Nan)	+/- 0	1
    x<0	y, not integer	QNaN
    |x|<1	-infinity	+infinity
    |x|>1	-infinity	+0
    |x|<1	+infinity	+0
    |x|>1	+infinity	+infinity
    -infinity	y<0, odd integer	-0
    -infinity	y<0, not odd integer	+0
    -infinity	y>0, odd integer	-infinity
    -infinity	y>0, not odd integer	+infinity
    +infinity	y<0,	+0
    +infinity	y>0,	+infinity
    NaN	y nonzero,	NaN
    x<>1	NaN,	NaN

• Performance:
  • 400 cycles for most valid inputs (100 cycles per value).