Refactor bus_t::load/store for DRY

riscv/devices.cc

@@ -10,53 +10,43 @@ mmio_device_map_t& mmio_device_map()
 
 void bus_t::add_device(reg_t addr, abstract_device_t* dev)
 {
-  // Searching devices via lower_bound/upper_bound
-  // implicitly relies on the underlying std::map 
-  // container to sort the keys and provide ordered
-  // iteration over this sort, which it does. (python's
-  // SortedDict is a good analogy)
   devices[addr] = dev;
 }
 
 bool bus_t::load(reg_t addr, size_t len, uint8_t* bytes)
 {
-  // Find the device with the base address closest to but
-  // less than addr (price-is-right search)
-  auto it = devices.upper_bound(addr);
-  if (devices.empty() || it == devices.begin()) {
-    // Either the bus is empty, or there weren't 
-    // any items with a base address <= addr
-    return false;
-  }
-  // Found at least one item with base address <= addr
-  // The iterator points to the device after this, so
-  // go back by one item.
-  it--;
-  return it->second->load(addr - it->first, len, bytes);
+  if (auto [base, dev] = find_device(addr, len); dev)
+    return dev->load(addr - base, len, bytes);
+  return false;
 }
 
 bool bus_t::store(reg_t addr, size_t len, const uint8_t* bytes)
 {
-  // See comments in bus_t::load
-  auto it = devices.upper_bound(addr);
-  if (devices.empty() || it == devices.begin()) {
-    return false;
-  }
-  it--;
-  return it->second->store(addr - it->first, len, bytes);
+  if (auto [base, dev] = find_device(addr, len); dev)
+    return dev->store(addr - base, len, bytes);
+  return false;
 }
 
 std::pair<reg_t, abstract_device_t*> bus_t::find_device(reg_t addr)
 {
-  // See comments in bus_t::load
+  // Obtain iterator to device immediately after the one that might match
   auto it = devices.upper_bound(addr);
   if (devices.empty() || it == devices.begin()) {
+    // No devices with base address <= addr
     return std::make_pair((reg_t)0, (abstract_device_t*)NULL);
   }
+
+  // Rewind to device that will match if its size suffices
   it--;
+
   return std::make_pair(it->first, it->second);
 }
 
+std::pair<reg_t, abstract_device_t*> bus_t::find_device(reg_t addr, size_t len)
+{
+  return find_device(addr);
+}
+
 mem_t::mem_t(reg_t size)
   : sz(size)
 {

riscv/devices.h

@@ -21,6 +21,7 @@ class bus_t : public abstract_device_t {
   void add_device(reg_t addr, abstract_device_t* dev);
 
   std::pair<reg_t, abstract_device_t*> find_device(reg_t addr);
+  std::pair<reg_t, abstract_device_t*> find_device(reg_t addr, size_t len);
 
  private:
   std::map<reg_t, abstract_device_t*> devices;