sub and add repr in c

sub-add.c

#include <stdio.h>
#include <stdint.h>

uint8_t da(uint8_t value) {
    uint8_t lo = value & 0x0F;
    uint8_t hi = value >> 4;
    if (lo > 9) lo += 6;
    if (hi > 9) hi += 6;
    return (hi << 4) | lo;
}

void subtract(uint8_t* R0, uint8_t* R1, uint8_t* DPTR) {
    uint8_t R7 = 0x03; // loop counter set to 3 so that we can process 4 bytes
    uint8_t A; // acc for ops

    for (; R7 > 0; R7--) {
        uint8_t PSW = 0; // simulating psw here, assuming it includes carry flag

        PSW &= ~0x01; // clear carry flag
        A = 0x99; // set acc to 0x99

        // subtract with borrow
        if (PSW & 0x01) { // check if carry is set
            A = A - *R1 - 1; // if it is, subtract 1 from the result
        } else {
            A = A - *R1; // if not, just subtract
        }

        // restore carry flag
        PSW |= (A > 0x99) ? 0x01 : 0x00;

        // add with carry
        if (PSW & 0x01) {
            A = A + *R0 + 1; // if carry is set, add 1 to the result
        } else {
            A = A + *R0; // if not, just add
        }

        // decimal adjust (assuming adjusts acc for bcd)
        A = da(A); // placeholder for decimal adjust operation

        // store result and increment pointers
        *DPTR = A;
        DPTR++;
        R1++;
        R0++;
    }
}

int main() {
    uint8_t dataX[4] = {0x03, 0x01, 0x07, 0x04};
    uint8_t dataY[4] = {0x02, 0x05, 0x03, 0x06};
    uint8_t results[4] = {0}; // to store results

    subtract(dataX, dataY, results);

    printf("results:\n");
    for (int i = 0; i < 4; i++) {
        printf("result[%d] = %02X\n", i, results[i]);
    }

    return 0;
}