// my_predictor.h
// This file contains a sample my_predictor class.
// It is a simple 32,768-entry gshare with a history length of 15.
// Note that this predictor doesn't use the whole 32 kilobytes available
// for the CBP-2 contest; it is just an example.

class my_update : public branch_update {
public:
	unsigned int index;
};

class my_predictor : public branch_predictor {
public:
#define HISTORY_LENGTH	15
#define TABLE_BITS	15
	my_update u;
	branch_info bi;
	unsigned int history;
	unsigned char tab[1<<TABLE_BITS];

	my_predictor (void) : history(0) { 
		memset (tab, 0, sizeof (tab));
	}

	branch_update *predict (branch_info & b) {
		bi = b;
		if (b.br_flags & BR_CONDITIONAL) {
			u.index = 
				  (history << (TABLE_BITS - HISTORY_LENGTH)) 
				^ (b.address & ((1<<TABLE_BITS)-1));
			u.direction_prediction (tab[u.index] >> 1);
		} else {
			u.direction_prediction (true);
		}
		u.target_prediction (0);
		return &u;
	}

	void update (branch_update *u, bool taken, unsigned int target) {
		if (bi.br_flags & BR_CONDITIONAL) {
			unsigned char *c = &tab[((my_update*)u)->index];
			if (taken) {
				if (*c < 3) (*c)++;
			} else {
				if (*c > 0) (*c)--;
			}
			history <<= 1;
			history |= taken;
			history &= (1<<HISTORY_LENGTH)-1;
		}
	}
};