Compute the approximate reciprocal square root of the lower single-precision (32-bit) floating-point element in a,
store the result in the lower element. Copy the upper 3 packed elements from a to the upper elements of result.
The maximum relative error for this approximation is less than 1.5*2^-12.
Compute the approximate reciprocal square root of the lower single-precision (32-bit) floating-point element in a, store the result in the lower element. Copy the upper 3 packed elements from a to the upper elements of result. The maximum relative error for this approximation is less than 1.5*2^-12.