zx-generation/src/instructions/logical.js

A high-fidelity ZX Spectrum emulator in JavaScript — fully generated by a large language model (LLM) to explore the boundaries of AI in systems programming.

/**
 * Logical Instructions
 * Handles AND, OR, XOR, CPL, SCF, CCF, DAA operations
 */
class LogicalInstructions {
    constructor(registers, flags) {
        this.registers = registers;
        this.flags = flags;
    }

    /**
     * AND A, value
     */
    andA(value) {
        const result = this.registers.get('A') & value;
        this.registers.set('A', result);

        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.C, false);
        newF = this.flags.setFlag(newF, this.flags.masks.H, true);
        newF = this.flags.updateFlags(newF, result, 'logical');
        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * OR A, value
     */
    orA(value) {
        const result = this.registers.get('A') | value;
        this.registers.set('A', result);

        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.C, false);
        newF = this.flags.setFlag(newF, this.flags.masks.H, false);
        newF = this.flags.updateFlags(newF, result, 'logical');
        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * XOR A, value
     */
    xorA(value) {
        const result = this.registers.get('A') ^ value;
        this.registers.set('A', result);

        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.C, false);
        newF = this.flags.setFlag(newF, this.flags.masks.H, false);
        newF = this.flags.updateFlags(newF, result, 'logical');
        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * CPL (Complement A)
     */
    cpl() {
        this.registers.set('A', ~this.registers.get('A') & 0xff);

        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.H, true);
        newF = this.flags.setFlag(newF, this.flags.masks.N, true);

        // Undocumented flags from A
        const a = this.registers.get('A');
        newF = this.flags.setFlag(newF, this.flags.masks.F5, (a & 0x20) !== 0);
        newF = this.flags.setFlag(newF, this.flags.masks.F3, (a & 0x08) !== 0);

        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * SCF (Set Carry Flag)
     */
    scf() {
        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.C, true);
        newF = this.flags.setFlag(newF, this.flags.masks.H, false);
        newF = this.flags.setFlag(newF, this.flags.masks.N, false);

        // Undocumented flags from A
        const a = this.registers.get('A');
        newF = this.flags.setFlag(newF, this.flags.masks.F5, (a & 0x20) !== 0);
        newF = this.flags.setFlag(newF, this.flags.masks.F3, (a & 0x08) !== 0);

        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * CCF (Complement Carry Flag)
     */
    ccf() {
        const oldCarry = this.flags.getFlag(this.registers.get('F'), this.flags.masks.C);

        let newF = this.registers.get('F');
        newF = this.flags.setFlag(newF, this.flags.masks.H, oldCarry);
        newF = this.flags.setFlag(newF, this.flags.masks.C, !oldCarry);
        newF = this.flags.setFlag(newF, this.flags.masks.N, false);

        // Undocumented flags from A
        const a = this.registers.get('A');
        newF = this.flags.setFlag(newF, this.flags.masks.F5, (a & 0x20) !== 0);
        newF = this.flags.setFlag(newF, this.flags.masks.F3, (a & 0x08) !== 0);

        this.registers.set('F', newF);

        return 4; // cycles
    }

    /**
     * DAA (Decimal Adjust Accumulator)
     *
     * Flags affected: S Z H PV N C F5 F3
     * This is the official Z80 logic for DAA.
     * - H is set if there is a half-carry out of bit 3 of the result (after correction)
     * - C is set if correction was >= 0x60, or if C was already set and a correction was done
     * - N is not changed
     */
    daa() {
        let a = this.registers.get('A');
        let f = this.registers.get('F');

        const c = this.flags.getFlag(f, this.flags.masks.C);
        const h = this.flags.getFlag(f, this.flags.masks.H);
        const n = this.flags.getFlag(f, this.flags.masks.N);

        let correction = 0;
        let setC = false;

        // DAA algorithm
        if (!n) {
            // After addition
            if (h || (a & 0x0f) > 9) {
                correction |= 0x06;
            }
            if (c || a > 0x99) {
                correction |= 0x60;
                setC = true;
            }

            const newA = (a + correction) & 0xff;
            // Set or clear H: was there a half-carry?
            const halfCarry = (a & 0x0f) + (correction & 0x0f) > 0x0f;
            f = this.flags.setFlag(f, this.flags.masks.H, halfCarry);
            a = newA;
        } else {
            // After subtraction - DAA adjusts based on invalid BCD digits
            if (h) {
                correction |= 0x06;
            }
            if (c) {
                correction |= 0x60;
            }

            const newA = (a - correction) & 0xff;
            // H flag behavior after subtraction DAA is complex:
            // Set if there was a borrow from bit 4 during the correction
            const halfBorrow = (a & 0x0f) < (correction & 0x0f);
            f = this.flags.setFlag(f, this.flags.masks.H, halfBorrow);
            a = newA;
            
            // C flag remains as it was (set by the previous SUB/SBC)
            setC = c;
        }

        // Set S, Z, PV
        f = this.flags.setFlag(f, this.flags.masks.S, (a & 0x80) !== 0);
        f = this.flags.setFlag(f, this.flags.masks.Z, a === 0);
        f = this.flags.setFlag(f, this.flags.masks.PV, this.flags.calculateParity(a));

        // Set/clear carry
        f = this.flags.setFlag(f, this.flags.masks.C, setC);

        // F5/F3 undocumented: from result
        f = this.flags.setFlag(f, this.flags.masks.F5, (a & 0x20) !== 0);
        f = this.flags.setFlag(f, this.flags.masks.F3, (a & 0x08) !== 0);

        this.registers.set('A', a);
        this.registers.set('F', f);

        return 4; // cycles
    }
}

export { LogicalInstructions };