public static FuncDef FindFunction(Context ctx, string name, int nameLength, int args, TEXTENCODE encode, bool createFlag)
{
Debug.Assert(args >= -2);
Debug.Assert(args >= -1 || !createFlag);
Debug.Assert(encode == TEXTENCODE.UTF8 || encode == TEXTENCODE.UTF16LE || encode == TEXTENCODE.UTF16BE);
int h = (char.ToLowerInvariant(name[0]) + nameLength) % ctx.Funcs.data.Length; // Hash value
// First search for a match amongst the application-defined functions.
FuncDef best = null; // Best match found so far
int bestScore = 0; // Score of best match
FuncDef p = FunctionSearch(ctx.Funcs, h, name, nameLength);
while (p != null)
{
int score = MatchQuality(p, args, encode);
if (score > bestScore)
{
best = p;
bestScore = score;
}
p = p.Next;
}
// If no match is found, search the built-in functions.
//
// If the SQLITE_PreferBuiltin flag is set, then search the built-in functions even if a prior app-defined function was found. And give
// priority to built-in functions.
//
// Except, if createFlag is true, that means that we are trying to install a new function. Whatever FuncDef structure is returned it will
// have fields overwritten with new information appropriate for the new function. But the FuncDefs for built-in functions are read-only.
// So we must not search for built-ins when creating a new function.
if (createFlag && (best == null || (ctx.Flags & Context.FLAG.PreferBuiltin) != 0))
{
FuncDefHash hash = sqlite3GlobalFunctions;
bestScore = 0;
p = FunctionSearch(hash, h, name, nameLength);
while (p != null)
{
int score = MatchQuality(p, args, encode);
if (score > bestScore)
{
best = p;
bestScore = score;
}
p = p.Next;
}
}
// If the createFlag parameter is true and the search did not reveal an exact match for the name, number of arguments and encoding, then add a
// new entry to the hash table and return it.
if (createFlag && bestScore < FUNC_PERFECT_MATCH && (best = new FuncDef()) != null)
{
best.Name = name;
best.Args = (short)args;
best.PrefEncode = encode;
FuncDefInsert(ctx.Funcs, best);
}
return(best != null && (best.Step != null || best.Func != null || createFlag) ? best : null);
}
static FuncDef FunctionSearch(FuncDefHash hash, int h, string func, int funcLength)
{
for (FuncDef p = hash[h]; p != null; p = p.Hash)
{
if (p.Name.Length == funcLength && p.Name.StartsWith(func, StringComparison.OrdinalIgnoreCase))
{
return(p);
}
}
return(null);
}
public static void FuncDefInsert(FuncDefHash hash, FuncDef def)
{
int nameLength = def.Name.Length;
int h = (char.ToLowerInvariant(def.Name[0]) + nameLength) % hash.data.Length;
FuncDef other = FunctionSearch(hash, h, def.Name, nameLength);
if (other != null)
{
Debug.Assert(other != def && other.Next != def);
def.Next = other.Next;
other.Next = def;
}
else
{
def.Next = null;
def.Hash = hash[h];
hash[h] = def;
}
}
