diff --git a/hw/ioapic.c b/hw/ioapic.c
index 705803c..4f96caf 100644
--- a/hw/ioapic.c
+++ b/hw/ioapic.c
@@ -39,20 +39,48 @@
 
 #define MAX_IOAPICS                     1
 
-#define IOAPIC_LVT_MASKED               (1 << 16)
-#define IOAPIC_LVT_REMOTE_IRR           (1 << 14)
+#define IOAPIC_VERSION                  0x11
 
-#define IOAPIC_TRIGGER_EDGE		0
-#define IOAPIC_TRIGGER_LEVEL		1
+#define IOAPIC_LVT_DEST_SHIFT           56
+#define IOAPIC_LVT_MASKED_SHIFT         16
+#define IOAPIC_LVT_TRIGGER_MODE_SHIFT   15
+#define IOAPIC_LVT_REMOTE_IRR_SHIFT     14
+#define IOAPIC_LVT_POLARITY_SHIFT       13
+#define IOAPIC_LVT_DELIV_STATUS_SHIFT   12
+#define IOAPIC_LVT_DEST_MODE_SHIFT      11
+#define IOAPIC_LVT_DELIV_MODE_SHIFT     8
+
+#define IOAPIC_LVT_MASKED               (1 << IOAPIC_LVT_MASKED_SHIFT)
+#define IOAPIC_LVT_REMOTE_IRR           (1 << IOAPIC_LVT_REMOTE_IRR_SHIFT)
+
+#define IOAPIC_TRIGGER_EDGE             0
+#define IOAPIC_TRIGGER_LEVEL            1
 
 /*io{apic,sapic} delivery mode*/
-#define IOAPIC_DM_FIXED			0x0
-#define IOAPIC_DM_LOWEST_PRIORITY	0x1
-#define IOAPIC_DM_PMI			0x2
-#define IOAPIC_DM_NMI			0x4
-#define IOAPIC_DM_INIT			0x5
-#define IOAPIC_DM_SIPI			0x5
-#define IOAPIC_DM_EXTINT		0x7
+#define IOAPIC_DM_FIXED                 0x0
+#define IOAPIC_DM_LOWEST_PRIORITY       0x1
+#define IOAPIC_DM_PMI                   0x2
+#define IOAPIC_DM_NMI                   0x4
+#define IOAPIC_DM_INIT                  0x5
+#define IOAPIC_DM_SIPI                  0x6
+#define IOAPIC_DM_EXTINT                0x7
+#define IOAPIC_DM_MASK                  0x7
+
+#define IOAPIC_VECTOR_MASK              0xff
+
+#define IOAPIC_IOREGSEL                 0x00
+#define IOAPIC_IOWIN                    0x10
+
+#define IOAPIC_REG_ID                   0x00
+#define IOAPIC_REG_VER                  0x01
+#define IOAPIC_REG_ARB                  0x02
+#define IOAPIC_REG_REDTBL_BASE          0x10
+#define IOAPIC_ID                       0x00
+
+#define IOAPIC_ID_SHIFT                 24
+#define IOAPIC_ID_MASK                  0xf
+
+#define IOAPIC_VER_ENTRIES_SHIFT        16
 
 typedef struct IOAPICState IOAPICState;
 
@@ -60,7 +88,6 @@ struct IOAPICState {
     SysBusDevice busdev;
     uint8_t id;
     uint8_t ioregsel;
-
     uint32_t irr;
     uint64_t ioredtbl[IOAPIC_NUM_PINS];
     uint64_t default_base_address;
@@ -86,21 +113,22 @@ static void ioapic_service(IOAPICState *s)
         if (s->irr & mask) {
             entry = s->ioredtbl[i];
             if (!(entry & IOAPIC_LVT_MASKED)) {
-                trig_mode = ((entry >> 15) & 1);
-                dest = entry >> 56;
-                dest_mode = (entry >> 11) & 1;
-                delivery_mode = (entry >> 8) & 7;
-                polarity = (entry >> 13) & 1;
+                trig_mode = ((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1);
+                dest = entry >> IOAPIC_LVT_DEST_SHIFT;
+                dest_mode = (entry >> IOAPIC_LVT_DEST_MODE_SHIFT) & 1;
+                delivery_mode =
+                    (entry >> IOAPIC_LVT_DELIV_MODE_SHIFT) & IOAPIC_DM_MASK;
+                polarity = (entry >> IOAPIC_LVT_POLARITY_SHIFT) & 1;
                 if (trig_mode == IOAPIC_TRIGGER_EDGE) {
                     s->irr &= ~mask;
                 } else {
                     s->ioredtbl[i] |= IOAPIC_LVT_REMOTE_IRR;
                 }
-                if (delivery_mode == IOAPIC_DM_EXTINT)
+                if (delivery_mode == IOAPIC_DM_EXTINT) {
                     vector = pic_read_irq(isa_pic);
-                else
-                    vector = entry & 0xff;
-
+                } else {
+                    vector = entry & IOAPIC_VECTOR_MASK;
+                }
                 apic_deliver_irq(dest, dest_mode, delivery_mode,
                                  vector, polarity, trig_mode);
             }
@@ -116,15 +144,16 @@ static void ioapic_set_irq(void *opaque, int vector, int level)
      * to GSI 2.  GSI maps to ioapic 1-1.  This is not
      * the cleanest way of doing it but it should work. */
 
-    DPRINTF("%s: %s vec %x\n", __func__, level? "raise" : "lower", vector);
-    if (vector == 0)
+    DPRINTF("%s: %s vec %x\n", __func__, level ? "raise" : "lower", vector);
+    if (vector == 0) {
         vector = 2;
-
+    }
     if (vector >= 0 && vector < IOAPIC_NUM_PINS) {
         uint32_t mask = 1 << vector;
         uint64_t entry = s->ioredtbl[vector];
 
-        if ((entry >> 15) & 1) {
+        if (((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1) ==
+            IOAPIC_TRIGGER_LEVEL) {
             /* level triggered */
             if (level) {
                 s->irr |= mask;
@@ -155,7 +184,8 @@ void ioapic_eio_broadcast(int vector)
         }
         for (n = 0; n < IOAPIC_NUM_PINS; n++) {
             entry = s->ioredtbl[n];
-            if ((entry & IOAPIC_LVT_REMOTE_IRR) && (entry & 0xff) == vector) {
+            if ((entry & IOAPIC_LVT_REMOTE_IRR)
+                && (entry & IOAPIC_VECTOR_MASK) == vector) {
                 s->ioredtbl[n] = entry & ~IOAPIC_LVT_REMOTE_IRR;
                 if (!(entry & IOAPIC_LVT_MASKED) && (s->irr & (1 << n))) {
                     ioapic_service(s);
@@ -171,65 +201,71 @@ static uint32_t ioapic_mem_readl(void *opaque, target_phys_addr_t addr)
     int index;
     uint32_t val = 0;
 
-    addr &= 0xff;
-    if (addr == 0x00) {
+    switch (addr & 0xff) {
+    case IOAPIC_IOREGSEL:
         val = s->ioregsel;
-    } else if (addr == 0x10) {
+        break;
+    case IOAPIC_IOWIN:
         switch (s->ioregsel) {
-            case 0x00:
-                val = s->id << 24;
-                break;
-            case 0x01:
-                val = 0x11 | ((IOAPIC_NUM_PINS - 1) << 16); /* version 0x11 */
-                break;
-            case 0x02:
-                val = 0;
-                break;
-            default:
-                index = (s->ioregsel - 0x10) >> 1;
-                if (index >= 0 && index < IOAPIC_NUM_PINS) {
-                    if (s->ioregsel & 1)
-                        val = s->ioredtbl[index] >> 32;
-                    else
-                        val = s->ioredtbl[index] & 0xffffffff;
+        case IOAPIC_REG_ID:
+            val = s->id << IOAPIC_ID_SHIFT;
+            break;
+        case IOAPIC_REG_VER:
+            val = IOAPIC_VERSION |
+                ((IOAPIC_NUM_PINS - 1) << IOAPIC_VER_ENTRIES_SHIFT);
+            break;
+        case IOAPIC_REG_ARB:
+            val = 0;
+            break;
+        default:
+            index = (s->ioregsel - IOAPIC_REG_REDTBL_BASE) >> 1;
+            if (index >= 0 && index < IOAPIC_NUM_PINS) {
+                if (s->ioregsel & 1) {
+                    val = s->ioredtbl[index] >> 32;
+                } else {
+                    val = s->ioredtbl[index] & 0xffffffff;
                 }
+            }
         }
         DPRINTF("read: %08x = %08x\n", s->ioregsel, val);
+        break;
     }
     return val;
 }
 
-static void ioapic_mem_writel(void *opaque, target_phys_addr_t addr, uint32_t val)
+static void
+ioapic_mem_writel(void *opaque, target_phys_addr_t addr, uint32_t val)
 {
     IOAPICState *s = opaque;
     int index;
 
-    addr &= 0xff;
-    if (addr == 0x00)  {
+    switch (addr & 0xff) {
+    case IOAPIC_IOREGSEL:
         s->ioregsel = val;
-        return;
-    } else if (addr == 0x10) {
+        break;
+    case IOAPIC_IOWIN:
         DPRINTF("write: %08x = %08x\n", s->ioregsel, val);
         switch (s->ioregsel) {
-            case 0x00:
-                s->id = (val >> 24) & 0xff;
-                return;
-            case 0x01:
-            case 0x02:
-                return;
-            default:
-                index = (s->ioregsel - 0x10) >> 1;
-                if (index >= 0 && index < IOAPIC_NUM_PINS) {
-                    if (s->ioregsel & 1) {
-                        s->ioredtbl[index] &= 0xffffffff;
-                        s->ioredtbl[index] |= (uint64_t)val << 32;
-                    } else {
-                        s->ioredtbl[index] &= ~0xffffffffULL;
-                        s->ioredtbl[index] |= val;
-                    }
-                    ioapic_service(s);
+        case IOAPIC_REG_ID:
+            s->id = (val >> IOAPIC_ID_SHIFT) & IOAPIC_ID_MASK;
+            break;
+        case IOAPIC_REG_VER:
+        case IOAPIC_REG_ARB:
+            break;
+        default:
+            index = (s->ioregsel - IOAPIC_REG_REDTBL_BASE) >> 1;
+            if (index >= 0 && index < IOAPIC_NUM_PINS) {
+                if (s->ioregsel & 1) {
+                    s->ioredtbl[index] &= 0xffffffff;
+                    s->ioredtbl[index] |= (uint64_t)val << 32;
+                } else {
+                    s->ioredtbl[index] &= ~0xffffffffULL;
+                    s->ioredtbl[index] |= val;
                 }
+                ioapic_service(s);
+            }
         }
+        break;
     }
 }
 
@@ -252,7 +288,7 @@ static const VMStateDescription vmstate_ioapic = {
     .post_load = ioapic_post_load,
     .minimum_version_id = 1,
     .minimum_version_id_old = 1,
-    .fields      = (VMStateField []) {
+    .fields = (VMStateField[]) {
         VMSTATE_UINT8(id, IOAPICState),
         VMSTATE_UINT8(ioregsel, IOAPICState),
         VMSTATE_UINT64_V(current_base_address, IOAPICState, 2),
@@ -279,8 +315,9 @@ static void ioapic_reset(DeviceState *d)
     s->id = 0;
     s->ioregsel = 0;
     s->irr = 0;
-    for(i = 0; i < IOAPIC_NUM_PINS; i++)
-        s->ioredtbl[i] = 1 << 16; /* mask LVT */
+    for (i = 0; i < IOAPIC_NUM_PINS; i++) {
+        s->ioredtbl[i] = 1 << IOAPIC_LVT_MASKED_SHIFT;
+    }
 }
 
 static CPUReadMemoryFunc * const ioapic_mem_read[3] = {
