mem: Add a helper function to get a word of variable length

There are many devices that need to handle reads/writes of different
word sizes. A common pattern is a switch statement that check for the
size of a packet and then calls the corresponding
Packet::(get|set)<uintXX_t> methods. Simplify this by implementing
Packet::(get|set)UintX helper functions.

The getter reads a word of the size specified in the packet and the
specified endianness. The word is then zero-extended to 64
bits. Conversely, the setter truncates the word down to the size
required in the packet and then byte-swaps it to the desired
endianness.

Change-Id: I2f0c27fe3903abf3859bea13b07c7f5f0fb0809f
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/9761
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/packet.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2017 ARM Limited
+ * Copyright (c) 2011-2018 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -56,6 +56,7 @@
 #include "base/cprintf.hh"
 #include "base/logging.hh"
 #include "base/trace.hh"
+#include "mem/packet_access.hh"
 
 using namespace std;
 
@@ -364,6 +365,45 @@ Packet::popSenderState()
     return sender_state;
 }
 
+uint64_t
+Packet::getUintX(ByteOrder endian) const
+{
+    switch(getSize()) {
+      case 1:
+        return (uint64_t)get<uint8_t>(endian);
+      case 2:
+        return (uint64_t)get<uint16_t>(endian);
+      case 4:
+        return (uint64_t)get<uint32_t>(endian);
+      case 8:
+        return (uint64_t)get<uint64_t>(endian);
+      default:
+        panic("%i isn't a supported word size.\n", getSize());
+    }
+}
+
+void
+Packet::setUintX(uint64_t w, ByteOrder endian)
+{
+    switch(getSize()) {
+      case 1:
+        set<uint8_t>((uint8_t)w, endian);
+        break;
+      case 2:
+        set<uint16_t>((uint16_t)w, endian);
+        break;
+      case 4:
+        set<uint32_t>((uint32_t)w, endian);
+        break;
+      case 8:
+        set<uint64_t>((uint64_t)w, endian);
+        break;
+      default:
+        panic("%i isn't a supported word size.\n", getSize());
+    }
+
+}
+
 void
 Packet::print(ostream &o, const int verbosity, const string &prefix) const
 {

src/mem/packet.hh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012-2017 ARM Limited
+ * Copyright (c) 2012-2018 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -1068,6 +1068,20 @@ class Packet : public Printable
     template <typename T>
     void set(T v);
 
+
+    /**
+     * Get the data in the packet byte swapped from the specified
+     * endianness and zero-extended to 64 bits.
+     */
+    uint64_t getUintX(ByteOrder endian) const;
+
+    /**
+     * Set the value in the word w after truncating it to the length
+     * of the packet and then byteswapping it to the desired
+     * endianness.
+     */
+    void setUintX(uint64_t w, ByteOrder endian);
+
     /**
      * Copy data into the packet from the provided pointer.
      */