Implements SBCS instruction#20
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Adds the SBCS (Subtract with Carry) instruction to the instruction decoder and arithmetic operations. This instruction performs subtraction with carry, taking into account the carry flag in the CPSR. A new opcode rule is added to the instruction decoder to map the instruction. Additionally, a test case is added to verify the instruction's correctness.
begeistert
requested changes
Feb 2, 2026
5 tasks
Implementing test when R0 should be 0 and also checking the substraction of negative result.
Fix the subtract-with-carry (SBC) operation in ArithmeticOps.cs to use AddWithFlags with the two's-complement operand and an explicit carry value. Previously the code attempted to compute SBC by subtracting (valRm + (1 - C)) via SubWithFlags, which produced incorrect flag behavior and was harder to reason about. Changes: - read carry into a local uint (carry = C ? 1 : 0) - call AddWithFlags(cpu, rdn, ~valRm, carry) to implement rdn - rm - (1 - C) using two's-complement addition This makes the implementation correct for borrow/carry handling and aligns with canonical SBC semantics while preserving CPU flags.
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begeistert
approved these changes
Feb 15, 2026
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Adds the SBCS (Subtract with Carry) instruction to the instruction decoder and arithmetic operations.
This instruction performs subtraction with carry, taking into account the carry flag in the CPSR. A new opcode rule is added to the instruction decoder to map the instruction. Additionally, a test case is added to verify the instruction's correctness.
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dotnet test)Screenshots / Hex Dumps (Optional)