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/* branch_predict.c -- branch prediction simulation
   Copyright (C) 1999 Damjan Lampret, lampret@opencores.org
 
This file is part of OpenRISC 1000 Architectural Simulator. 
 
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
 
/* Branch prediction functions. 
   At the moment this functions only simulate functionality of branch
   prediction and do not influence on fetche/decode/execute stages.
   They are here only to verify performance of various branch
   prediction configurations.
 
 */
 
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdarg.h>
 
#include "branch_predict.h"
#include "abstract.h"
#include "stats.h"
 
/* Branch prediction buffer */
 
/* Length of BPB */
#define BPB_LEN 32
 
/* Number of BPB ways (1, 2, 3 etc.). */
#define BPB_WAYS 2
 
/* Number of prediction states (2, 4, 8 etc.). */
#define BPB_PSTATES 2
 
/* Number of usage states (2, 3, 4 etc.). */
#define BPB_USTATES 2
 
/* branch prediction buffer entry */
struct bpb_entry {
	struct {
		unsigned long addr;	/* address of a branch insn */
		int taken;		/* taken == 1, not taken == 0  OR */
					/* strongly taken == 3, taken == 2, 
					   not taken == 1, strongly not taken == 0 */
		int lru;		/* least recently == 0 */
	} way[BPB_WAYS];
} bpb[BPB_LEN];
 
/* First check if branch is already in the cache and if it is:
    - increment BPB hit stats,
    - set 'lru' at this way to BPB_USTATES - 1 and
      decrement 'lru' of other ways unless they have reached 0,
    - increment correct/incorrect stats according to BPB 'taken' field
      and 'taken' variable,
    - increment or decrement BPB taken field according to 'taken' variable
   and if not:
    - increment BPB miss stats
    - find lru way and entry and replace old address with 'addr' and
      'taken' field with (BPB_PSTATES/2 - 1) + 'taken'
    - set 'lru' with BPB_USTATES - 1 and decrement 'lru' of other
      ways unless they have reached 0
*/
 
void bpb_update(unsigned long addr, int taken)
{
	int entry, way = -1;
	int i;
 
	/* Calc entry. */
	entry = addr % BPB_LEN;
 
	/* Scan all ways and try to find our addr. */
	for (i = 0; i < BPB_WAYS; i++)
		if (bpb[entry].way[i].addr == addr)
			way = i;
 
	/* Did we find our cached branch? */
	if (way >= 0) { /* Yes, we did. */
		mstats.bpb.hit++;
 
		for (i = 0; i < BPB_WAYS; i++)
			if (bpb[entry].way[i].lru)
				bpb[entry].way[i].lru--;
		bpb[entry].way[way].lru = BPB_USTATES - 1;
 
		if (bpb[entry].way[way].taken / (BPB_PSTATES / 2) == taken)
			mstats.bpb.correct++;
		else
			mstats.bpb.incorrect++;
 
		if (taken && (bpb[entry].way[way].taken < BPB_PSTATES - 1))
			bpb[entry].way[way].taken++;
		else
		if (!taken && (bpb[entry].way[way].taken))
			bpb[entry].way[way].taken--;	
	}
	else {	/* No, we didn't. */
		int minlru = BPB_USTATES - 1;
		int minway = 0;
 
                mstats.bpb.miss++;
 
		for (i = 0; i < BPB_WAYS; i++)
			if (bpb[entry].way[i].lru < minlru)
				minway = i;
 
		bpb[entry].way[minway].addr = addr;
		bpb[entry].way[minway].taken = (BPB_PSTATES / 2 - 1) + taken;
		for (i = 0; i < BPB_WAYS; i++)
			if (bpb[entry].way[i].lru)
				bpb[entry].way[i].lru--;
		bpb[entry].way[minway].lru = BPB_USTATES - 1;                
	}
}
 
/* Branch target instruction cache */
 
/* Length of BTIC */
#define BTIC_LEN 32
 
/* Number of BTIC ways (1, 2, 3 etc.). */
#define BTIC_WAYS 2
 
/* Number of usage states (2, 3, 4 etc.). */
#define BTIC_USTATES 2
 
struct btic_entry {
	struct {
		unsigned long addr;	/* cached target address of a branch */
		int lru;		/* least recently used */
		char *insn;		/* cached insn at target address (not used currently) */
	} way[BTIC_WAYS];
} btic[BTIC_LEN];
 
/* First check if target addr is already in the cache and if it is:
    - increment BTIC hit stats,
    - set 'lru' at this way to BTIC_USTATES - 1 and
      decrement 'lru' of other ways unless they have reached 0,
   and if not:
    - increment BTIC miss stats
    - find lru way and entry and replace old address with 'addr' and
      'insn' with NULL
    - set 'lru' with BTIC_USTATES - 1 and decrement 'lru' of other
      ways unless they have reached 0
*/
 
void btic_update(unsigned long targetaddr)
{
	int entry, way = -1;
	int i;
 
	/* Calc entry. */
	entry = targetaddr % BTIC_LEN;
 
	/* Scan all ways and try to find our addr. */
	for (i = 0; i < BTIC_WAYS; i++)
		if (btic[entry].way[i].addr == targetaddr)
			way = i;
 
	/* Did we find our cached branch? */
	if (way >= 0) { /* Yes, we did. */
		mstats.btic.hit++;
 
		for (i = 0; i < BTIC_WAYS; i++)
			if (btic[entry].way[i].lru)
				btic[entry].way[i].lru--;
		btic[entry].way[way].lru = BTIC_USTATES - 1;	
	}
	else {	/* No, we didn't. */
		int minlru = BTIC_USTATES - 1;
		int minway = 0;
 
                mstats.btic.miss++;
 
		for (i = 0; i < BTIC_WAYS; i++)
			if (btic[entry].way[i].lru < minlru)
				minway = i;
 
		btic[entry].way[minway].addr = targetaddr;
		btic[entry].way[minway].insn = NULL;
		for (i = 0; i < BTIC_WAYS; i++)
			if (btic[entry].way[i].lru)
				btic[entry].way[i].lru--;
		btic[entry].way[minway].lru = BTIC_USTATES - 1;                
	}
}