/*
** Record in the column cache that a particular column from a
** particular table is stored in a particular register.
*/
static void sqlite3ExprCacheStore( Parse pParse, int iTab, int iCol, int iReg )
{
int i;
int minLru;
int idxLru;
yColCache p = new yColCache();
Debug.Assert( iReg > 0 ); /* Register numbers are always positive */
Debug.Assert( iCol >= -1 && iCol < 32768 ); /* Finite column numbers */
/* The SQLITE_ColumnCache flag disables the column cache. This is used
** for testing only - to verify that SQLite always gets the same answer
** with and without the column cache.
*/
if ( ( pParse.db.flags & SQLITE_ColumnCache ) != 0 )
return;
/* First replace any existing entry.
**
** Actually, the way the column cache is currently used, we are guaranteed
** that the object will never already be in cache. Verify this guarantee.
*/
#if !NDEBUG
for ( i = 0; i < SQLITE_N_COLCACHE; i++ )//p=pParse.aColCache... p++)
{
#if FALSE //* This code wold remove the entry from the cache if it existed */
p = pParse.aColCache[i];
if ( p.iReg != 0 && p.iTable == iTab && p.iColumn == iCol )
{
cacheEntryClear( pParse, p );
p.iLevel = pParse.iCacheLevel;
p.iReg = iReg;
p.lru = pParse.iCacheCnt++;
return;
}
#endif
Debug.Assert( p.iReg == 0 || p.iTable != iTab || p.iColumn != iCol );
}
#endif
/* Find an empty slot and replace it */
for ( i = 0; i < SQLITE_N_COLCACHE; i++ )//p=pParse.aColCache... p++)
{
p = pParse.aColCache[i];
if ( p.iReg == 0 )
{
p.iLevel = pParse.iCacheLevel;
p.iTable = iTab;
p.iColumn = iCol;
p.iReg = iReg;
p.tempReg = 0;
p.lru = pParse.iCacheCnt++;
return;
}
}
/* Replace the last recently used */
minLru = 0x7fffffff;
idxLru = -1;
for ( i = 0; i < SQLITE_N_COLCACHE; i++ )//p=pParse.aColCache..., p++)
{
p = pParse.aColCache[i];
if ( p.lru < minLru )
{
idxLru = i;
minLru = p.lru;
}
}
if ( ALWAYS( idxLru >= 0 ) )
{
p = pParse.aColCache[idxLru];
p.iLevel = pParse.iCacheLevel;
p.iTable = iTab;
p.iColumn = iCol;
p.iReg = iReg;
p.tempReg = 0;
p.lru = pParse.iCacheCnt++;
return;
}
}
/*
** Clear a cache entry.
*/
static void cacheEntryClear( Parse pParse, yColCache p )
{
if ( p.tempReg != 0 )
{
if ( pParse.nTempReg < ArraySize( pParse.aTempReg ) )
{
pParse.aTempReg[pParse.nTempReg++] = p.iReg;
}
p.tempReg = 0;
}
}