Learn more about Fixed-Point Toolbox

Using fimath to Specify Rounding and Overflow Modes

Only rounding and overflow modes set prior to an operation with fi objects affect the outcome of those operations. Once you create a fi object in MATLAB, changing its rounding or overflow mode does not affect its value. For example, consider the fi objects a and b:

p = fipref('NumberDisplay', 'RealWorldValue',...
'NumericTypeDisplay', 'none', 'FimathDisplay', 'none');
T = numerictype('WordLength',8,'FractionLength',7);
F = fimath('RoundMode','floor','OverflowMode','wrap');
a = fi(1,T,F)
 
a =
 
    -1

b = fi(1,T)
 
b =
 
    0.9922

Because you create a with a fimath object F that has OverflowMode set to wrap, the value of a wraps to -1. Conversely, because you create b with the default OverflowMode value of saturate, its value saturates to 0.9922.

Now, assign the fimath object F to b:

b.fimath = F
 
b =
 
    0.9922

Because the assignment operation and corresponding overflow and saturation happened when you created b, its value does not change when you assign it the new fimath object F.

Note   fi objects that are associated with the global fimath and created from a floating-point value always get constructed with a RoundMode of nearest and an OverflowMode of saturate. To construct fi objects with different RoundMode and OverflowMode properties, specify the desired RoundMode and OverflowMode properties in the fi constructor.

Using fimath Properties to Perform Fixed-Point Arithmetic

Using fimath to Share Arithmetic Rules

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