Bug 4: Upside-Down Arithmetic Shift
- We are isolating and sign-extending a bit field.
- The bit field offsets are: at, at+1, at+2, ..., at+ct-1
- We shift the field until its highest bit is at offset 63.
- Then we shift the field until its lowest bit is at offset 0.
- The latter is an arithmetic shift to extend the sign bit.
Fix The Tiny Bug In This Go Code: