From: Axel Friedrich <lists@...>
Date: 2012-12-11T17:22:40+09:00
Subject: Re: Binary Fixed-Point in Ruby? (Improved FixedPt?)

Hi Brian,

many thanks for your answer.!

>> fi = FixedPt.new(0.1,5,7)
>
> What are the 5 and 7 meant to signify?

This means:
* Use 5 Bits, and
* The binary point (similar to the "decimal point") is assumed to be
between the 7th and 8th bit, counting from right.

In the above example, it is like this:
A value of decimal 0.1 shall be handled by hardware.
The hardware (FPGA, actually) handels these bits (representing not
exactly decimal 0.1):
01100 (5 Bits)
The logic is designed in such a way, that these bits represent the
following value:
0.0001100 (binary point between the 7th and 8th bit from right)


> class FixBin
>   def initialize(value, binbits)
>     @value = (value * (1 << binbits)).to_i
>     @binbits = binbits
>   end
>   def to_f
>     @value * 1.0 / (1 << @binbits)
>   end
>   def to_s
>     res = "%0#{@binbits+1}b" % @value
>     res[-@binbits,0] = "."
>     res
>   end
> end

That's a very neat and elegant way! Thank you for that. I think, I'll
modify the existing "fixedpt.rb" file for my needs, with your code in
mind.


Axel

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