void xchg_mb_border(uint8_t *top_border, uint8_t *src_y, uint8_t *src_cb,
                    uint8_t *src_cr, ptrdiff_t linesize, ptrdiff_t uvlinesize, int mb_x,
                    int mb_y, int mb_width, int simple, int xchg)
{
    uint8_t *top_border_m1 = top_border - 32;     // for TL prediction
    src_y  -= linesize;
    src_cb -= uvlinesize;
    src_cr -= uvlinesize;

#define XCHG(a, b, xchg)                                                      \
    do {                                                                      \
        if (xchg)                                                             \
            AV_SWAP64(b, a);                                                  \
        else                                                                  \
            AV_COPY64(b, a);                                                  \
    } while (0)

    XCHG(top_border_m1 + 8, src_y - 8, xchg);
    XCHG(top_border, src_y, xchg);
    XCHG(top_border + 8, src_y + 8, 1);
    if (mb_x < mb_width - 1)
        XCHG(top_border + 32, src_y + 16, 1);

    if (!simple || !mb_y) {
        XCHG(top_border_m1 + 16, src_cb - 8, xchg);
        XCHG(top_border_m1 + 24, src_cr - 8, xchg);
        XCHG(top_border + 16, src_cb, 1);
        XCHG(top_border + 24, src_cr, 1);
    }
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.