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Some ARM and Thumb instructions perform saturating arithmetic.
The saturating instructions are:
Some of the parallel instructions are also saturating.
Saturation means that, for some value of
n that depends on the instruction:
For a signed saturating operation, if the full result would be less
n, the result
returned is -2
For an unsigned saturating operation, if the full result would be negative, the result returned is zero.
If the full result would be greater than 2
n-1, the result returned is 2
When any of these occurs, it is called saturation. Some instructions set the Q flag when saturation occurs.
The Q flag can also be set by two other instructions, but these instructions do not saturate.