Q (number format) Multiply

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I know "CONV_STD_LOGIC_VECTOR" will not work with a 64 bit value, just using this as an example.

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This is only because of the limitations of the integer type. If you kept it all in the unsiged (or even better for this application, the ufixed type) there are no limitiations.

Basically, to do what you want, you cannot use integers at all, because they are so large. You will get an overflow error when you try and similate because the result of multiplying the two integers is too large.