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fimath for Sharing Arithmetic Rules

There are two ways of sharing fimath properties in Fixed-Point Designer™ software:

Sharing fimath properties across fi objects ensures that the fi objects are using the same arithmetic rules and helps you avoid “mismatched fimath” errors.

Default fimath Usage to Share Arithmetic Rules

You can ensure that your fi objects are all using the same fimath properties by not specifying any local fimath. To assure no local fimath is associated with a fi object, you can:

  • Create a fi object using the fi constructor without specifying any fimath properties in the constructor call. For example: 

    a = fi(pi)

  • Create a fi object using the sfi or ufi constructor. All fi objects created with these constructors have no local fimath.

    b = sfi(pi)

  • Use removefimath to remove a local fimath object from an existing fi object.

Local fimath Usage to Share Arithmetic Rules

You can also use a fimath object to define common arithmetic rules that you would like to use for multiple fi objects. You can then create your fi objects, using the same fimath object for each. To do so, you must also create a numerictype object to define a common data type and scaling. Refer to numerictype Object Construction for more information on numerictype objects. The following example shows the creation of a numerictype object and fimath object, and then uses those objects to create two fi objects with the same numerictype and fimath attributes:

T = numerictype('WordLength', 32, 'FractionLength', 30)
T =


          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 30
F = fimath('RoundingMethod', 'Floor', 'OverflowAction', 'Wrap')
F = 


        RoundingMethod: Floor
        OverflowAction: Wrap
           ProductMode: FullPrecision
               SumMode: FullPrecision
a = fi(pi, T, F)
a = 

   -0.8584

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 30

        RoundingMethod: Floor
        OverflowAction: Wrap
           ProductMode: FullPrecision
               SumMode: FullPrecision
b = fi(pi/2, T, F)
b = 

    1.5708

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 30

        RoundingMethod: Floor
        OverflowAction: Wrap
           ProductMode: FullPrecision
               SumMode: FullPrecision