Analog Devices ADSP-BF53x Blackfin, Reference

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ADSP-BF53x/BF56x Blackfin Processor Programming Reference 1-17
Introduction
Saturation
When the result of an arithmetic operation exceeds the range of the desti-
nation register, important information can be lost.
Saturation is a technique used to contain the quantity within the values
that the destination register can represent. When a value is computed that
exceeds the capacity of the destination register, then the value written to
the register is the largest value that the register can hold with the same sign
as the original.
• If an operation would otherwise cause a positive value to overflow
and become negative, instead, saturation limits the result to the
maximum positive value for the size register being used.
• Conversely, if an operation would otherwise cause a negative value
to overflow and become positive, saturation limits the result to the
maximum negative value for the register size.
The overflow arithmetic flag is never set by an operation that enforces
saturation.
Figure 1-2. Conventional Placement of Binal Point
binal point alignment
S
S
S 8-bit extension
40-bit accumulator
32-bit register
16-bit register half
31-bit fraction
31-bit fraction
15-bit fraction