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Forum: FPGA, VHDL & Verilog FLoating point multiplier Logicore


von Misbah F. (Company: fast) (mis6358)


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Does any one know the function of floating point multiplier in logicore? 
its not giving me accurate answers i want to know how it works and how 
it gives the answer and in what form

von Lothar M. (lkmiller) (Moderator)


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What manual do you use as reference? What information are you missing 
there? What results do you expect and what results do you get?

von Rolf S. (audiorolf)


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"Logicore" is Xilinx, right? You will have to provide code and an 
example to make people be able to help you.

von Misbah F. (Company: fast) (mis6358)


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I am using the manual which is provided on the xilinx site. A want a 
answer of a simple multiplier like 1.2 x 1.2 should give me 2.4 in 
binary at the output but it is giving me some dummy values.

von Misbah F. (Company: fast) (mis6358)


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There is no code. I am using schematics. A simple floating point 
multiplier in the schematics.

von Klaus Falser (Guest)


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Misbah Faiz wrote:
> I am using the manual which is provided on the xilinx site. A want
> a
> answer of a simple multiplier like 1.2 x 1.2 should give me 2.4 in
> binary at the output but it is giving me some dummy values.

I'm not surprised.
1.2 x 1.2 gives 1.44 in my understanding.

von AHED (Guest)


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I suppose

"1.2" means a signed fractional format with 1 integer bit and 2 
fractional bits.
When multiplying two such numbers using a 3-bit signed integer 
multiplier the result has to be interpreted as "2.4".

However, when dealing with floating point ( normalized mantissa, || < 
1.0 )
the multiplication result is usually modified by dropping the unused 
MSbits
so that "1.4" is left. Now, the new additional LSbits ( in this case 2 ) 
that cannot be represented in the destination format which is usually 
the same as the input format "1.2" are dropped as well ( possibly after 
rounding )

This might explain the confusion

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