static void pcnet_bcr_writew(PCNetState *s, uint32_t rap, uint32_t val)
{
    rap &= 127;
#ifdef PCNET_DEBUG_BCR
    printf("pcnet_bcr_writew rap=%d val=0x%04x\n", rap, val);
#endif
    switch (rap) {
    case BCR_SWS:
        if (!(CSR_STOP(s) || CSR_SPND(s)))
            return;
        val &= ~0x0300;
        switch (val & 0x00ff) {
        case 0:
            val |= 0x0200;
            break;
        case 1:
            val |= 0x0100;
            break;
        case 2:
        case 3:
            val |= 0x0300;
            break;
        default:
            printf("Bad SWSTYLE=0x%02x\n", val & 0xff);
            val = 0x0200;
            break;
        }
#ifdef PCNET_DEBUG
       printf("BCR_SWS=0x%04x\n", val);
#endif
        /* fall through */
    case BCR_LNKST:
    case BCR_LED1:
    case BCR_LED2:
    case BCR_LED3:
    case BCR_MC:
    case BCR_FDC:
    case BCR_BSBC:
    case BCR_EECAS:
    case BCR_PLAT:
        s->bcr[rap] = val;
        break;
    default:
        break;
    }
}

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.