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Diffstat (limited to 'cpu/beta_cpu/2bit_local_pred.hh')
-rw-r--r-- | cpu/beta_cpu/2bit_local_pred.hh | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/cpu/beta_cpu/2bit_local_pred.hh b/cpu/beta_cpu/2bit_local_pred.hh new file mode 100644 index 000000000..32a7972d0 --- /dev/null +++ b/cpu/beta_cpu/2bit_local_pred.hh @@ -0,0 +1,99 @@ +#ifndef __2BIT_LOCAL_PRED_HH__ +#define __2BIT_LOCAL_PRED_HH__ + +// For Addr type. +#include "arch/alpha/isa_traits.hh" + +class DefaultBP +{ + public: + /** + * Default branch predictor constructor. + */ + DefaultBP(unsigned localPredictorSize, unsigned localCtrBits, + unsigned instShiftAmt); + + /** + * Looks up the given address in the branch predictor and returns + * a true/false value as to whether it is taken. + * @param branch_addr The address of the branch to look up. + * @return Whether or not the branch is taken. + */ + bool lookup(Addr &branch_addr); + + /** + * Updates the branch predictor with the actual result of a branch. + * @param branch_addr The address of the branch to update. + * @param taken Whether or not the branch was taken. + */ + void update(Addr &branch_addr, bool taken); + + private: + + inline bool getPrediction(uint8_t &count); + + inline unsigned getLocalIndex(Addr &PC); + + /** + * Private counter class for the internal saturating counters. + * Implements an n bit saturating counter and provides methods to + * increment, decrement, and read it. + * @todo Consider making this something that more closely mimics a + * built in class so you can use ++ or --. + */ + class SatCounter + { + public: + /** + * Constructor for the counter. + * @param bits How many bits the counter will have. + */ + SatCounter(unsigned bits); + + /** + * Constructor for the counter. + * @param bits How many bits the counter will have. + * @param initial_val Starting value for each counter. + */ + SatCounter(unsigned bits, unsigned initial_val); + + /** + * Increments the counter's current value. + */ + void increment(); + + /** + * Decrements the counter's current value. + */ + void decrement(); + + /** + * Read the counter's value. + */ + uint8_t read() + { + return counter; + } + + private: + uint8_t maxVal; + uint8_t counter; + }; + + /** Array of counters that make up the local predictor. */ + SatCounter *localCtrs; + + /** Size of the local predictor. */ + unsigned localPredictorSize; + + /** Number of bits of the local predictor's counters. */ + unsigned localCtrBits; + + /** Number of bits to shift the PC when calculating index. */ + unsigned instShiftAmt; + + /** Mask to get index bits. */ + unsigned indexMask; +}; + +#endif // __2BIT_LOCAL_PRED_HH__ |