Fix SBC carry flag calculation#1
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garry-jeromson wants to merge 1 commit intoElectronicsTinkerer:mainfrom
Open
Fix SBC carry flag calculation#1garry-jeromson wants to merge 1 commit intoElectronicsTinkerer:mainfrom
garry-jeromson wants to merge 1 commit intoElectronicsTinkerer:mainfrom
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The carry flag was being calculated using the modified accumulator value instead of the original value. For SBC, carry should be set if no borrow occurred (A >= M + (1 - C_in)), which requires using the original A and carry values before the subtraction. Save original A and C at the start of the function and use them for the carry calculation. This fixes unsigned comparisons that rely on the carry flag after SBC. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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The carry flag was being calculated using the modified accumulator value instead of the original value. For SBC, carry should be set if no borrow occurred (A >= M + (1 - C_in)), which requires using the original A and carry values before the subtraction.
Save original A and C at the start of the function and use them for the carry calculation. This fixes unsigned comparisons that rely on the carry flag after SBC.