Re: twos complement and the CF (carry flag)

LuB wrote:

Or do mean the generating hardware? For a subtraction the Carry
generated by the adder has to be inverted to produce the correct Carry.

Ahhhhhh, do you mean ... when using SUB we must invert the resulting
CARRY FLAG? IE: if CARRY FLAG=0, then invert that ... so CARRY FLAG=1.


We want a-b but we calculate
a + 2th complement(b) = a + (2^8-b) = 2^8 + (a-b)
so, if a>=b we get a Carry because of the 2^8 and if a<b we don't
get a Carry because the Carry of the subtraction is neutralized
by the 2^8. To get the correct Carry, we have to invert the Carry
generated by the adder.
.

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