Convert the signed 64-bit integer b to a double-precision (64-bit) floating-point element, store the result in the lower element of result, and copy the upper element from a to the upper element of result.
See Implementation
Convert the signed 64-bit integer b to a double-precision (64-bit) floating-point element, store the result in the lower element of result, and copy the upper element from a to the upper element of result.