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Altera_Forum
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13 years ago

Subtraction with numeric_Std doesn't work

Hello What am i doing in wrong in the code below. subtraction doesn't work! I am using numeric_std and the numbers are in twos complement format. // mattgust library ieee; use ieee....
Altera_Forum's avatar
Altera_Forum
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13 years ago

You need the opcode to generate overflow signal. I give you some rules:

a-If your adding and the operands have oposite signs an overflow NEVER occurs.

b-If your adding and the operands have the same sign and the result has the same sign too, there are NO overflow.

c-If your adding and the operands have the same sign and the result has oposite same sign, there ARE overflow.

e-If your substracting and the operands have the same sign an overflow NEVER occurs.

f-If your substracting and the operands have oposite sign, but the result has same sign as first operand, there are NO overflow.

g-If your substracting and the operands have oposite sign, but the result has oposite sign as first operand, there ARE overflow.