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# N [[Negative flag]]. Set to a copy of the most significant bit of an arithmetic result.
# V [[Overflow flag]]. Set in case of two's complement overflow.
# S Sign flag. Unique to AVR, this is always
# H [[Half-carry flag]]. This is an internal carry from additions and is used to support [[Binary-coded decimal|BCD]] arithmetic.
# T Bit copy. Special bit load and bit store instructions use this bit.
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There are two special cases which exist to facilitate multi-byte arithmetic:
* The <code>INC</code> and <code>DEC</code> instructions do ''not'' modify the carry flag, so they may be used to loop over [[arbitrary-precision arithmetic]] operands.<ref name="isa_manual">{{cite web |url=
* The <code>CPC</code>, <code>SBC</code> and <code>SBCI</code> (compare/subtract with carry) instructions do ''not'' set the Z flag when the result is zero, but only clear it if the result is non-zero.{{r|isa_manual|p=79,147,149}} For ''fixed'' precision multi-byte comparisons, implemented with an [[Loop unrolling|unrolled]] <code>CP; CPC; CPC; CPC</code> sequence, this produces a zero flag which is set only if the ''entire'' difference is zero.
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