# Converting from floating point to fixed point.

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ON on 27 Sep 2022
Moved: Walter Roberson on 27 Sep 2022
How can i convert from floating point to two's complement? I need to convert a vector of filter coefficients from Filter Designer but I do not know how.

Walter Roberson on 27 Sep 2022
The Fixed Point Toolbox fi() can be used to create a variety of fixed point formats.
If you need to match a particular hardware fixed point format for a dsp then we would need to know the details of the representation.
##### 1 CommentShowHide None
Walter Roberson on 27 Sep 2022
Moved: Walter Roberson on 27 Sep 2022
format long g
BitsAfterDecimalPoint = 12;
Value = -0.0126842654631061924064283630286809057
Value =
-0.0126842654631062
encoded = int16(Value * 2^BitsAfterDecimalPoint)
encoded = int16
-52
decoded = double(encoded) / 2^BitsAfterDecimalPoint
decoded =
-0.0126953125
abs(Value - decoded)
ans =
1.10470368938076e-05
There is a limit to how much precision you can get with 16 bits...
BitsAfterDecimalPoint = 16;
encoded = int16(Value * 2^BitsAfterDecimalPoint)
encoded = int16
-831
decoded = double(encoded) / 2^BitsAfterDecimalPoint
decoded =
-0.0126800537109375
abs(Value - decoded)
ans =
4.21175216869241e-06

### More Answers (1)

ON on 27 Sep 2022
I need to convert for example -0.0126842654631061924064283630286809057 into a 16 bit signed value.
##### 1 CommentShowHide None
Walter Roberson on 27 Sep 2022
int16(Value * 2^BitsAfterDecimalPoint)

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