End-Around Carry (EAC) Correction - 1's Complement Addition:

In 1's complement, negative numbers are bitwise complements. When adding, a carry out of MSB is not discarded but added back to LSB (end-around carry).

Rule: Add numbers as unsigned. If carry-out $C_{out}=1$, add 1 to result to get correct sum.

Example: Add $+5$ (0101) and $-3$ (1100 in 1's complement):
0101 + 1100 = 10001 -> 4-bit result 0001 with $C_{out}=1$. Add EAC: 0001+1 = 0010 (2), which is correct ($5-3=2$).

If no carry ($C_{out}=0$), result is already correct and negative (1's complement) if MSB=1. Double complement case $1111$ represents -0.