Exponential code in VHDL

[Zaid Al-Hilli]

Hi all,

I am about implementing a VHDL code but I am facing problem, I have an
exponential operation and I want to run that code op an FPGA board!!

Generally speaking the assignment is: X = (1 / (1+ exp((y + 87.8) /
8.5)));

Would you please help me in that?

Many thanks in advance...

Zaid

 

[Benjamin Couillard]

Hi all,

I am about implementing a VHDL code but I am facing problem, I have an
exponential operation and I want to run that code op an FPGA board!!

Generally speaking the assignment is:  X = (1 / (1+ exp((y + 87.8) /
8.5)));

Would you please help me in that?

Many thanks in advance...

Zaid

One simple way would be to use a look-up table implemented in a ROM.
With "y" being the address and X being the data read at "y" address.
This solution would work well if the range of "y" in bits is smaller
or equal to 16 bits. If "y" is 32-bit wide then I don't think a look-
up table implemented in a FPGA-Rom will work.

 

[noobie]

Hi all,

I am about implementing a VHDL code but I am facing problem, I have an
exponential operation and I want to run that code op an FPGA board!!

Generally speaking the assignment is:  X = (1 / (1+ exp((y + 87.8) /
8.5)));

Would you please help me in that?

Many thanks in advance...

Zaid

Use Taylor series expansion for the calculation of this equation. Use
fixed point arithmetic.

 

[jeppe]

Find inspiration here:

http://users-tima.imag.fr/cis/guyot/Cours/Oparithm/english/Fonctio.htm

Jeppe

 

[RADNOR]

figure out at least something by yourself about your homework assignment before posting a lameass question like "how to do it"

 

[Zaid Al-Hilli]

One simple way would be to use a look-up table implemented in a ROM.
With "y" being the address and X being the data read at "y" address.
This solution would work well if the range of "y" in bits is smaller
or equal to 16 bits. If "y" is 32-bit wide then I don't think a look-
up table implemented in a FPGA-Rom will work.

Thanks a lot!

 

[Zaid Al-Hilli]

Yeah, bound the range of y sufficiently that you can implement the
entire thing in a RAM lookup table.

Thanks a lot!