The default settings of the fimath object offer the smallest
rounding error and prevent overflows. However, they can result in extra logic in
generated code. These default settings are:
RoundingMethod: Nearest
OverflowAction: Saturate
ProductMode: FullPrecision
SumMode: FullPrecision
For leaner code, it is recommended that you match the
fimath settings to the settings of your processor.
The KeepLSB setting for ProductMode
and SumMode models the behavior of integer operations in
the C language. KeepMSB for
ProductMode models the behavior of many DSP
devices.
Different rounding methods require different amounts of overhead code.
Setting the RoundingMethod property to
Floor, which is equivalent to two’s complement
truncation, provides the most efficient rounding implementation for most
operations. For the divide function, the most efficient
RoundingMethod is Zero.
The standard method for handling overflows is to wrap using modulo
arithmetic. Other overflow handling methods create costly logic. It is
recommended that you set the OverflowAction property to
Wrap when possible.
The CORDIC-based algorithms are among the most hardware friendly because they require only iterative shift-add operations. Replacing functions with one of the CORDIC implementations can make your generated code more efficient. For a list of the CORDIC functions, and examples of them being implemented, see CORDIC Algorithms.
You can implement some functions more efficiently by using a lookup table approach. For an example, see Implement Fixed-Point Log2 Using Lookup Table.
Division is often not supported by hardware. When possible, it is best to avoid division operations.
When the denominator is a power of two, you can rewrite the division as a bit shift operation.
x/8
can be rewritten as
bitsra(x,3)
Other times it is more efficient to implement division as a multiplication by a reciprocal.
x/5
can be rewritten as
x*0.2