LUT mask in arithmetic mode LE

[wayne]

When LE is in arithmetic mode it is not clear how the mask is calculated. In theory, Carry Equation should determine the generation of the carry bit, and Sum Equation determine the bit of the sum. However, in my experience, Sum Equation duplicates the first byte of Carry Equation.

The screenshot shows one of the LE adders.

According to my calculations, the Carry Equation should be

(A&B) # ((A # B) & C) therefore the Carry LUT mask should be E8E8.

However, in the screenshot i see a completely different result.

[RichardTanSY_Intel]

Hi, could you try to simulate in Modelsim and check whether the function works or not?

[wayne]

Probably have to do so, but it is strange that there is no detailed information on this problem anywhere.

It’s still not clear why Sum Equation repeats the first bit of Carry Equation