/***************************************************
NAME : HashExpression
DESCRIPTION : Assigns a deterministic number to
an expression
INPUTS : The expression
RETURNS : The "value" of the expression
SIDE EFFECTS : None
NOTES : None
***************************************************/
static unsigned HashExpression(
EXPRESSION *exp)
{
unsigned long tally = PRIME_THREE;
if (exp->argList != NULL)
tally += HashExpression(exp->argList) * PRIME_ONE;
while (exp != NULL)
{
tally += (unsigned long) (exp->type * PRIME_TWO);
tally += (unsigned long) exp->value;
exp = exp->nextArg;
}
return((unsigned) (tally % EXPRESSION_HASH_SIZE));
}
/***************************************************
NAME : FindHashedExpression
DESCRIPTION : Determines if a given expression
is in the expression hash table
INPUTS : 1) The expression
2) A buffer to hold the hash
value
3) A buffer to hold the previous
node in the hash chain
RETURNS : The expression hash table entry
(NULL if not found)
SIDE EFFECTS : None
NOTES : None
***************************************************/
static EXPRESSION_HN *FindHashedExpression(
EXPRESSION *exp,
unsigned *hashval,
EXPRESSION_HN **prv)
{
EXPRESSION_HN *exphash;
if (exp == NULL)
return(NULL);
*hashval = HashExpression(exp);
*prv = NULL;
exphash = ExpressionHashTable[*hashval];
while (exphash != NULL)
{
if (IdenticalExpression(exphash->exp,exp))
return(exphash);
*prv = exphash;
exphash = exphash->nxt;
}
return(NULL);
}
/***************************************************
NAME : HashExpression
DESCRIPTION : Assigns a deterministic number to
an expression
INPUTS : The expression
RETURNS : The "value" of the expression
SIDE EFFECTS : None
NOTES : None
***************************************************/
static unsigned HashExpression(
EXPRESSION *theExp)
{
unsigned long tally = PRIME_THREE;
union
{
void *vv;
unsigned long uv;
} fis;
if (theExp->argList != NULL)
tally += HashExpression(theExp->argList) * PRIME_ONE;
while (theExp != NULL)
{
tally += (unsigned long) (theExp->type * PRIME_TWO);
fis.uv = 0;
fis.vv = theExp->value;
tally += fis.uv;
theExp = theExp->nextArg;
}
return((unsigned) (tally % EXPRESSION_HASH_SIZE));
}
