1 files changed, 110 insertions, 0 deletions
diff --git a/cpu/beta_cpu/2bit_local_pred.cc b/cpu/beta_cpu/2bit_local_pred.cc
new file mode 100644
index 000000000..88c39a9b0
--- /dev/null
+++ b/cpu/beta_cpu/2bit_local_pred.cc
@@ -0,0 +1,110 @@
+#include "base/trace.hh"
+#include "cpu/beta_cpu/2bit_local_pred.hh"
+
+DefaultBP::SatCounter::SatCounter(unsigned bits)
+    : maxVal((1 << bits) - 1), counter(0)
+{
+}
+
+DefaultBP::SatCounter::SatCounter(unsigned bits, unsigned initial_val)
+    : maxVal((1 << bits) - 1), counter(initial_val)
+{
+    // Check to make sure initial value doesn't exceed the max counter value.
+    if (initial_val > maxVal) {
+        panic("BP: Initial counter value exceeds max size.");
+    }
+}
+
+void
+DefaultBP::SatCounter::increment()
+{
+    if(counter < maxVal) {
+        ++counter;
+    }
+}
+
+void
+DefaultBP::SatCounter::decrement()
+{
+    if(counter > 0) {
+        --counter;
+    }
+}
+
+DefaultBP::DefaultBP(unsigned _localPredictorSize,
+                     unsigned _localCtrBits,
+                     unsigned _instShiftAmt)
+    : localPredictorSize(_localPredictorSize),
+      localCtrBits(_localCtrBits),
+      instShiftAmt(_instShiftAmt)
+{
+    // Should do checks here to make sure sizes are correct (powers of 2).
+
+    // Setup the index mask.
+    indexMask = localPredictorSize - 1;
+
+    DPRINTF(Fetch, "Branch predictor: index mask: %#x\n", indexMask);
+
+    // Setup the array of counters for the local predictor.
+    localCtrs = new SatCounter[localPredictorSize](localCtrBits);
+
+    DPRINTF(Fetch, "Branch predictor: local predictor size: %i\n",
+            localPredictorSize);
+
+    DPRINTF(Fetch, "Branch predictor: local counter bits: %i\n", localCtrBits);
+
+    DPRINTF(Fetch, "Branch predictor: instruction shift amount: %i\n",
+            instShiftAmt);
+}
+
+inline
+bool
+DefaultBP::getPrediction(uint8_t &count)
+{
+    // Get the MSB of the count
+    return (count >> (localCtrBits - 1));
+}
+
+inline
+unsigned
+DefaultBP::getLocalIndex(Addr &branch_addr)
+{
+    return (branch_addr >> instShiftAmt) & indexMask;
+}
+
+bool
+DefaultBP::lookup(Addr &branch_addr)
+{
+    uint8_t local_prediction;
+    unsigned local_predictor_idx = getLocalIndex(branch_addr);
+
+    DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n",
+            local_predictor_idx);
+
+    local_prediction = localCtrs[local_predictor_idx].read();
+
+    DPRINTF(Fetch, "Branch predictor: prediction is %i.\n",
+            (int)local_prediction);
+
+    return getPrediction(local_prediction);
+}
+
+void
+DefaultBP::update(Addr &branch_addr, bool taken)
+{
+    unsigned local_predictor_idx;
+
+    // Update the local predictor.
+    local_predictor_idx = getLocalIndex(branch_addr);
+
+    DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n",
+            local_predictor_idx);
+
+    if (taken) {
+        DPRINTF(Fetch, "Branch predictor: Branch updated as taken.\n");
+        localCtrs[local_predictor_idx].increment();
+    } else {
+        DPRINTF(Fetch, "Branch predictor: Branch updated as not taken.\n");
+        localCtrs[local_predictor_idx].decrement();
+    }
+}