fi Object Properties

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Data Properties fimath Properties numerictype Properties Setting fi Object Properties

Data Properties

The data properties of a fi object are always writable.

• bin — Stored integer value of a fi object in binary

• data — Numerical real-world value of a fi object

• dec — Stored integer value of a fi object in decimal

• double — Real-world value of a fi object, stored as a MATLAB double data type

• hex — Stored integer value of a fi object in hexadecimal

• oct — Stored integer value of a fi object in octal

To learn more about these properties, see fi Object Properties in the Fixed-Point Toolbox Reference.

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fimath Properties

In general, the fimath properties associated with fi objects depend on how you create the fi object:

• When you specify one or more fimath object properties in the fi constructor, the resulting fi object has a local fimath object.

• When you do not specify any fimath object properties in the fi constructor, the resulting fi object has no local fimath.

To determine whether a fi object has a local fimath object, use the isfimathlocal function.

The fimath properties associated with fi objects determine how fixed-point arithmetic is performed. These fimath properties can come from a local fimath object or from default fimath property values. To learn more about fimath objects in fixed-point arithmetic, see fimath Rules for Fixed-Point Arithmetic.

The following fimath properties are, by transitivity, also properties of the fi object. You can set these properties for individual fi objects. The following fimath properties are always writable.

• CastBeforeSum — Whether both operands are cast to the sum data type before addition

  Note   This property is hidden when the SumMode is set to FullPrecision.

• MaxProductWordLength — Maximum allowable word length for the product data type

• MaxSumWordLength — Maximum allowable word length for the sum data type

• OverflowMode — Overflow mode

• ProductBias — Bias of the product data type

• ProductFixedExponent — Fixed exponent of the product data type

• ProductFractionLength — Fraction length, in bits, of the product data type

• ProductMode — Defines how the product data type is determined

• ProductSlope — Slope of the product data type

• ProductSlopeAdjustmentFactor — Slope adjustment factor of the product data type

• ProductWordLength — Word length, in bits, of the product data type

• RoundMode — Rounding mode

• SumBias — Bias of the sum data type

• SumFixedExponent — Fixed exponent of the sum data type

• SumFractionLength — Fraction length, in bits, of the sum data type

• SumMode — Defines how the sum data type is determined

• SumSlope — Slope of the sum data type

• SumSlopeAdjustmentFactor — Slope adjustment factor of the sum data type

• SumWordLength — The word length, in bits, of the sum data type

To learn more about these properties, see the fimath Object Properties in the Fixed-Point Toolbox Reference.

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numerictype Properties

When you create a fi object, a numerictype object is also automatically created as a property of the fi object:

numerictype — Object containing all the data type information of a fi object, Simulink signal or model parameter

The following numerictype properties are, by transitivity, also properties of a fi object. The following properties of the numerictype object become read only after you create the fi object. However, you can create a copy of a fi object with new values specified for the numerictype properties:

• Bias — Bias of a fi object

• DataType — Data type category associated with a fi object

• DataTypeMode — Data type and scaling mode of a fi object

• FixedExponent — Fixed-point exponent associated with a fi object

• FractionLength — Fraction length of the stored integer value of a fi object in bits

• Scaling — Fixed-point scaling mode of a fi object

• Signed — Whether a fi object is signed or unsigned

• Signedness — Whether a fi object is signed or unsigned

  Note   numerictype objects can have a Signedness of Auto, but all fi objects must be Signed or Unsigned. If a numerictype object with Auto Signedness is used to create a fi object, the Signedness property of the fi object automatically defaults to Signed.

• Slope — Slope associated with a fi object

• SlopeAdjustmentFactor — Slope adjustment associated with a fi object

• WordLength — Word length of the stored integer value of a fi object in bits

For further details on these properties, see the Property Reference.

There are two ways to specify properties for fi objects in Fixed-Point Toolbox software. Refer to the following sections:

• Setting Fixed-Point Properties at Object Creation

• Using Direct Property Referencing with fi

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Setting fi Object Properties

You can set fi object properties in two ways:

• Setting the properties when you create the object

• Using direct property referencing

Setting Fixed-Point Properties at Object Creation

You can set properties of fi objects at the time of object creation by including properties after the arguments of the fi constructor function. For example, to set the overflow mode to wrap and the rounding mode to convergent,

a = fi(pi, 'OverflowMode', 'wrap', 'RoundMode', 'convergent') 

a =
 
    3.1416


          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 13

             RoundMode: convergent
          OverflowMode: wrap
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128

Using Direct Property Referencing with fi

You can reference directly into a property for setting or retrieving fi object property values using MATLAB structure-like referencing. You do so by using a period to index into a property by name.

For example, to get the WordLength of a,

a.WordLength

ans =

    16

To set the OverflowMode of a,

a.OverflowMode = 'wrap' 

a =
 
    3.1416


          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 13

             RoundMode: convergent
          OverflowMode: wrap
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128

If you have a fi object b with a local fimath object, you can remove the local fimath object and force b to use default fimath values:

b = fi(pi, 1, 'RoundMode', 'Floor')

b =
    3.1415

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 13

             RoundMode: floor
          OverflowMode: saturate
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128

b.fimath = []

b =
    3.1415

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 13

isfimathlocal(b)

ans =
     0

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Casting fi Objects

fi Object Functions

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