Learn more about Fixed-Point Toolbox

Using fimath to Share Arithmetic Rules

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

• Using the Global fimath to Share Arithmetic Rules

• Using fimath Objects to Share Arithmetic Rules

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

Using the Global fimath to Share Arithmetic Rules

You can ensure that your fi objects are all using the same fimath properties by associating them with the global fimath. To associate a fi object with the global fimath, you can:

• Create a fi object using the fi constructor, and do not specify 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 associate themselves with the global fimath.

  b = sfi(pi)

• Use dot notation to remove an attached fimath object from an existing fi object. Doing so automatically associates the fi object with the global fimath. For example:

  b = fi(pi, 'RoundMode', 'Fix')
  b.fimath = []	

To learn how to configure the global fimath, see Working with the Global fimath.

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Using fimath Objects 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 Working with numerictype Objects 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('RoundMode', 'floor', 'OverflowMode', 'wrap') 
 
F =
 

             RoundMode: floor
          OverflowMode: wrap
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128
         CastBeforeSum: true

a = fi(pi, T, F)
 
a =
 
   -0.8584


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

             RoundMode: floor
          OverflowMode: wrap
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128
         CastBeforeSum: true
 
b = fi(pi/2, T, F)
 
b =
 
    1.5708


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

             RoundMode: floor
          OverflowMode: wrap
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128
         CastBeforeSum: true

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Using fimath to Specify Rounding and Overflow Modes

Using fimath ProductMode and SumMode

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