Round Mr Register; Saturate Mr Register On Overflow - Analog Devices ADSP-2106x SHARC User Manual

2 Computation Units

2.6.3.2 Round MR Register

Rounding of a fixed-point result occurs either as part of a multiply or
multiply/accumulate operation or as an explicit operation on the MR
register. The rounding operation applies only to fractional results (integer
results are not affected) and rounds the 80-bit MR value to nearest at bit
32, i.e. at the MR1-MR0 boundary. The rounded result in MR1 can be sent
either to the register file or back to the same MR register. To round a
fractional result to zero (truncation) instead of to nearest, you would
simply transfer the unrounded result from MR1, discarding the lower 32
bits in MR0.

2.6.3.3 Saturate MR Register On Overflow

The saturate operation sets MR to a maximum value if the MR value has
overflowed. Overflow occurs when the MR value is greater than the
maximum value for the data format (unsigned or twos-complement and
integer or fractional) that is specified in the saturate instruction. There are
six possible maximum values (shown in hexadecimal):
MR2 MR1
Maximum twos-complement fractional number
0000 7FFF FFFF
FFFF 8000 0000
Maximum twos-complement integer number
0000 0000 0000
FFFF FFFF FFFF
Maximum unsigned fractional number
0000 FFFF FFFF
Maximum unsigned integer number
0000 0000 0000
The result from MR saturation can be sent either to the register file or back
to the same MR register.
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MR0
FFFF FFFF positive
0000 0000 negative
7FFF FFFF positive
8000 0000 negative
FFFF FFFF
FFFF FFFF