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Fixed point coder log10 implementation

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Jogger
Jogger on 19 Nov 2020
Answered: Jogger on 26 Dec 2020 at 5:17
I am using 20*log10(val) to get power in a dB
y = 20*log10(3)
But When i am using matlab coder to convert the in c/c++ code.I am gettig an error
Function 'log10' is not defined for values of class 'embedded.fi'.
Can someone help me with alternate way of doing dB calculation.
Thank you

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Accepted Answer

Jogger
Jogger on 26 Dec 2020 at 5:17
qsb = fixed.Quantizer(numerictype(1,32,24));
y0 = quantize(qsb,20*fi(log(double(x)),1,32,24)/fi(log(double(10)),1,32,24)); % log(x)/log(10) for log base 10 i.e. log10
y1 = 20*log10(x);

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More Answers (2)

Darshan Ramakant Bhat
Darshan Ramakant Bhat on 19 Nov 2020
The function "log10" is supported for code generation in the latest version (R2020b) of MATLAB. You can find the list of supported functions in the below page :

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Jogger
Jogger on 19 Nov 2020
Thanks - I see, is there a way I can use with R2019b ?

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Jogger
Jogger on 20 Nov 2020
I made a test and I don't see the expected result
I am still getting the error following error
??? Function 'log10' is not defined for values of class 'embedded.fi'.
My question - did you verify log10 ?
Below is the matlab version
>> ver
-----------------------------------------------------------------------------------------------------
MATLAB Version: 9.9.0.1524771 (R2020b) Update 2
MATLAB License Number: 40523231
Operating System: Microsoft Windows 10 Enterprise Version 10.0 (Build 18363)
Java Version: Java 1.8.0_202-b08 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
-----------------------------------------------------------------------------------------------------
MATLAB Version 9.9 (R2020b)
Fixed-Point Designer Version 7.1 (R2020b)
HDL Coder Version 3.17 (R2020b)
HDL Verifier Version 6.2 (R2020b)
MATLAB Coder Version 5.1 (R2020b)
Parallel Computing Toolbox Version 7.3 (R2020b)

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Show 3 older comments
Jogger
Jogger on 20 Nov 2020
I think it is still wrong
y = 20*fi(log(double(3)),1,16,0)
&
y = 20*log10(3)
Jogger
Jogger on 20 Nov 2020
May I know what is the difference ?
Why No Fraction length ?
How did you arrive to the conclusion ?
what if y = 20*fi(log(double(x)),1,16,FL) is considerd ?if FL is 16- we get overflow but correct conversion value
Can please share the explanation in case of WL = 8,16,24,32,64- what should be the FL ?
What is range , slope , bias , resolution & precision in that case.
When do we see Overflow and Underflow . Why double is considerd that unsupported in fixed point converter?
I think log (Natural logarithm) is unsupported. We need common logarithm base 10.
How enable logging Mode fipref ? How it help me in verification
Can you please help?Thank you!
Jogger
Jogger on 21 Nov 2020
I found the right implementation -
qsb = fixed.Quantizer(numerictype(1,32,24));
y0 = quantize(qsb,20*fi(log(double(x)),1,32,24)/fi(log(double(10)),1,32,24)); % log(x)/log(10) for log base 10 i.e. log10
y1 = 20*log10(x);
Question - Matlab fixed point suggestion using fi(value) is not reliable .I don't know why it suggest that results in overflow.
You can try fi(3)
WL =16
FL= 13
Signedness =1
Try , you can see overflow. For me its not clear . Please help me
Thanks

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