Fixed point coder log10 implementation

2020 11 19
3 个回答
回答已采纳
更新时间：2020 12 26
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0 个投票

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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Life is Wonderful
Life is Wonderful 2020-12-26

0 个投票

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);

更多回答（2 个）

0 个投票

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 :
https://www.mathworks.com/help/referencelist.html?type=function&capability=codegen
Life is Wonderful
Life is Wonderful 2020-11-20

0 个投票

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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I tried with the below function and it worked in my MATLAB
function y = myLogFunc(x)
y = 20*log10(x);
end
>> codegen -config:lib myLogFunc -args {3} -report
Code generation successful: View report
Please provide me your sample function along with the script to reproduce the issue.
Life is Wonderful
Life is Wonderful 2020-11-20
编辑：Life is Wonderful 2020-11-20
i don't see you generating the Fix point matlab file ? For me - the problem is with coder app generating the fixpoint matlab script
Did you notice your C code still had double for nargin? You have to consider sign, WL and FL for your input and then feed to log10 . Another point for your notice - 20*log10 (x) is NOT fixed point-
Several compiler ask to log function as they won't include the log10 in math.h . For example of Linux based implementation.
Try following sequence
fixptcfg = coder.config('fixpt')
fixptcfg.TestBenchName = 'compute_log_tb';
cfg = coder.config('lib');
codegen -float2fixed fixptcfg -config cfg compute_log -args {3}
============= Step3: Generate Fixed Point Code ==============
### Generating Fixed Point MATLAB Code compute_log_fixpt using Proposed Types
### Generating Fixed Point MATLAB Design Wrapper compute_log_wrapper_fixpt
### Generating Mex file for ' compute_log_wrapper_fixpt '
??? Function 'log10' is not defined for values of class 'embedded.fi'.
Error in ==> compute_log_fixpt Line: 10 Column: 28
Code generation failed: View Error Report
Build failed.
Use help codegen for more information on using this command.
Thanks for attaching the sample script and explaining the issue clearly. I completely missed the fixed point conversion part earlier.
The error is happening because the function "log10()" cannot take the fixed point inputs. If you do "log10(fi(3))" it will error out.
I found below documentations on fixing such errors :
https://www.mathworks.com/help/fixedpoint/ug/what-to-do-when-a-function-is-not-supported-for-fixed-point-conversion.html
https://www.mathworks.com/help/fixedpoint/ug/manual-fixed-point-conversion-best-practices.html
https://www.mathworks.com/help/fixedpoint/ug/implement-fixed-point-log2-using-lookup-table.html
Based on the above doc I modified the function like below :
function y = compute_log(x)
%#codegen
y = 20*fi(log(double(x)),1,16,0);
end
Life is Wonderful
Life is Wonderful 2020-11-20
编辑：Life is Wonderful 2020-11-20
I think it is still wrong
y = 20*fi(log(double(3)),1,16,0)
&
y = 20*log10(3)
Life is Wonderful
Life is Wonderful 2020-11-20
编辑：Life is Wonderful 2020-11-20
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!
Life is Wonderful
Life is Wonderful 2020-11-21
编辑：Life is Wonderful 2020-11-21
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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