for (i = 0; i < mp_irq_entries; i++) {
                int lbus = mp_irqs[i].mpc_srcbus;
 
-               if (mp_bus_id_to_type[lbus] == MP_BUS_ISA &&
+               if (test_bit(lbus, mp_bus_not_pci) &&
                    (mp_irqs[i].mpc_irqtype == type) &&
                    (mp_irqs[i].mpc_srcbusirq == irq))
 
        for (i = 0; i < mp_irq_entries; i++) {
                int lbus = mp_irqs[i].mpc_srcbus;
 
-               if ((mp_bus_id_to_type[lbus] == MP_BUS_ISA) &&
+               if (test_bit(lbus, mp_bus_not_pci) &&
                    (mp_irqs[i].mpc_irqtype == type) &&
                    (mp_irqs[i].mpc_srcbusirq == irq))
                        break;
                            mp_irqs[i].mpc_dstapic == MP_APIC_ALL)
                                break;
 
-               if ((mp_bus_id_to_type[lbus] == MP_BUS_PCI) &&
+               if (!test_bit(lbus, mp_bus_not_pci) &&
                    !mp_irqs[i].mpc_irqtype &&
                    (bus == lbus) &&
                    (slot == ((mp_irqs[i].mpc_srcbusirq >> 2) & 0x1f))) {
        switch (mp_irqs[idx].mpc_irqflag & 3)
        {
                case 0: /* conforms, ie. bus-type dependent polarity */
-               {
-                       switch (mp_bus_id_to_type[bus])
-                       {
-                               case MP_BUS_ISA: /* ISA pin */
-                               {
-                                       polarity = default_ISA_polarity(idx);
-                                       break;
-                               }
-                               case MP_BUS_PCI: /* PCI pin */
-                               {
-                                       polarity = default_PCI_polarity(idx);
-                                       break;
-                               }
-                               default:
-                               {
-                                       printk(KERN_WARNING "broken BIOS!!\n");
-                                       polarity = 1;
-                                       break;
-                               }
-                       }
+                       if (test_bit(bus, mp_bus_not_pci))
+                               polarity = default_ISA_polarity(idx);
+                       else
+                               polarity = default_PCI_polarity(idx);
                        break;
-               }
                case 1: /* high active */
                {
                        polarity = 0;
        switch ((mp_irqs[idx].mpc_irqflag>>2) & 3)
        {
                case 0: /* conforms, ie. bus-type dependent */
-               {
-                       switch (mp_bus_id_to_type[bus])
-                       {
-                               case MP_BUS_ISA: /* ISA pin */
-                               {
-                                       trigger = default_ISA_trigger(idx);
-                                       break;
-                               }
-                               case MP_BUS_PCI: /* PCI pin */
-                               {
-                                       trigger = default_PCI_trigger(idx);
-                                       break;
-                               }
-                               default:
-                               {
-                                       printk(KERN_WARNING "broken BIOS!!\n");
-                                       trigger = 1;
-                                       break;
-                               }
-                       }
+                       if (test_bit(bus, mp_bus_not_pci))
+                               trigger = default_ISA_trigger(idx);
+                       else
+                               trigger = default_PCI_trigger(idx);
                        break;
-               }
                case 1: /* edge */
                {
                        trigger = 0;
        if (mp_irqs[idx].mpc_dstirq != pin)
                printk(KERN_ERR "broken BIOS or MPTABLE parser, ayiee!!\n");
 
-       switch (mp_bus_id_to_type[bus])
-       {
-               case MP_BUS_ISA: /* ISA pin */
-               {
-                       irq = mp_irqs[idx].mpc_srcbusirq;
-                       break;
-               }
-               case MP_BUS_PCI: /* PCI pin */
-               {
-                       /*
-                        * PCI IRQs are mapped in order
-                        */
-                       i = irq = 0;
-                       while (i < apic)
-                               irq += nr_ioapic_registers[i++];
-                       irq += pin;
-                       irq = gsi_irq_sharing(irq);
-                       break;
-               }
-               default:
-               {
-                       printk(KERN_ERR "unknown bus type %d.\n",bus); 
-                       irq = 0;
-                       break;
-               }
+       if (test_bit(bus, mp_bus_not_pci)) {
+               irq = mp_irqs[idx].mpc_srcbusirq;
+       } else {
+               /*
+                * PCI IRQs are mapped in order
+                */
+               i = irq = 0;
+               while (i < apic)
+                       irq += nr_ioapic_registers[i++];
+               irq += pin;
+               irq = gsi_irq_sharing(irq);
        }
        BUG_ON(irq >= NR_IRQS);
        return irq;
 
  * MP-table.
  */
 unsigned char apic_version [MAX_APICS];
-unsigned char mp_bus_id_to_type [MAX_MP_BUSSES] = { [0 ... MAX_MP_BUSSES-1] = -1 };
+DECLARE_BITMAP(mp_bus_not_pci, MAX_MP_BUSSES);
 int mp_bus_id_to_pci_bus [MAX_MP_BUSSES] = { [0 ... MAX_MP_BUSSES-1] = -1 };
 
 static int mp_current_pci_id = 0;
        Dprintk("Bus #%d is %s\n", m->mpc_busid, str);
 
        if (strncmp(str, "ISA", 3) == 0) {
-               mp_bus_id_to_type[m->mpc_busid] = MP_BUS_ISA;
+               set_bit(m->mpc_busid, mp_bus_not_pci);
        } else if (strncmp(str, "PCI", 3) == 0) {
-               mp_bus_id_to_type[m->mpc_busid] = MP_BUS_PCI;
+               clear_bit(m->mpc_busid, mp_bus_not_pci);
                mp_bus_id_to_pci_bus[m->mpc_busid] = mp_current_pci_id;
                mp_current_pci_id++;
        } else {
        /* 
         * Fabricate the legacy ISA bus (bus #31).
         */
-       mp_bus_id_to_type[MP_ISA_BUS] = MP_BUS_ISA;
-       Dprintk("Bus #%d is ISA\n", MP_ISA_BUS);
+       set_bit(MP_ISA_BUS, mp_bus_not_pci);
 
        /* 
         * Locate the IOAPIC that manages the ISA IRQs (0-15).