Atmel AVR instruction set: Difference between revisions

Revision as of 16:53, 16 May 2025

Revision as of 08:58, 17 May 2025

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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=httphttps://ww1.microchip.com/downloads/en/devicedocDeviceDoc/atmelAVR-0856InstructionSet-avrManual-instruction-set-manualDS40002198.pdf |title=AVR Instruction Set Manual |date=November 2016 |publisher=Atmel |id=Atmel-0856L |archive-url=https://web.archive.org/web/20241013184834/https://ww1.microchip.com/downloads/en/devicedoc/atmel-0856-avr-instruction-set-manual.pdf |archive-date=2024-10-13 |url-status=dead}}</ref>{{Rp|84,101}}

* 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.