In convergent rounding, the final result is rounded to the nearest even number (or odd number). In conventional implementations, if the midpoint is detected, then the units-placed bit before the round needs to be examined to determine whether the number is going to be rounded up or down.
- 2.5 rounds to 2 and –2.5 rounds to –2, but 1.5 rounds to 2 and –1.5 rounds to –2.
- 2.5 rounds to 3 and –2.5 rounds to –3, but 1.5 rounds to 1 and –1.5 rounds to –1.
The convergent rounding techniques require the use of programmable logic (PL) in addition to the DSP58. The different methods of implementing a convergent rounding scheme will be covered in a future revision of this document.