Fixed CORE-5480 - SUBSTRING startposition smaller than 1 should be allowed.

Author: asfernandes

src/dsql/ExprNodes.cpp

@@ -10282,17 +10282,6 @@ void SubstringNode::getDesc(thread_db* tdbb, CompilerScratch* csb, dsc* desc)
 		desc->dsc_flags |= DSC_null;
 	else
 	{
-		if (offsetNode->is<LiteralNode>() && desc1.dsc_dtype == dtype_long)
-		{
-			SLONG offset = MOV_get_long(&desc1, 0);
-
-			if (decrementNode && decrementNode->is<LiteralNode>() && desc3.dsc_dtype == dtype_long)
-				offset -= MOV_get_long(&desc3, 0);
-
-			if (offset < 0)
-				ERR_post(Arg::Gds(isc_bad_substring_offset) << Arg::Num(offset + 1));
-		}
-
 		if (length->is<LiteralNode>() && desc2.dsc_dtype == dtype_long)
 		{
 			const SLONG len = MOV_get_long(&desc2, 0);
@@ -10349,20 +10338,24 @@ dsc* SubstringNode::execute(thread_db* tdbb, jrd_req* request) const
 dsc* SubstringNode::perform(thread_db* tdbb, impure_value* impure, const dsc* valueDsc,
 	const dsc* startDsc, const dsc* lengthDsc)
 {
-	const SLONG sStart = MOV_get_long(startDsc, 0);
-	const SLONG sLength = MOV_get_long(lengthDsc, 0);
+	SINT64 sStart = MOV_get_long(startDsc, 0);
+	SINT64 sLength = MOV_get_long(lengthDsc, 0);
 
-	if (sStart < 0)
-		status_exception::raise(Arg::Gds(isc_bad_substring_offset) << Arg::Num(sStart + 1));
-	else if (sLength < 0)
+	if (sLength < 0)
 		status_exception::raise(Arg::Gds(isc_bad_substring_length) << Arg::Num(sLength));
 
+	if (sStart < 0)
+	{
+		sLength = MAX(sLength + sStart, 0);
+		sStart = 1;
+	}
+
+	FB_UINT64 start = FB_UINT64(sStart);
+	FB_UINT64 length = FB_UINT64(sLength);
+
 	dsc desc;
 	DataTypeUtil(tdbb).makeSubstr(&desc, valueDsc, startDsc, lengthDsc);
 
-	ULONG start = (ULONG) sStart;
-	ULONG length = (ULONG) sLength;
-
 	if (desc.isText() && length > MAX_STR_SIZE)
 		length = MAX_STR_SIZE;
 
@@ -10384,7 +10377,7 @@ dsc* SubstringNode::perform(thread_db* tdbb, impure_value* impure, const dsc* va
 		HalfStaticArray<UCHAR, BUFFER_LARGE> buffer;
 		CharSet* charSet = INTL_charset_lookup(tdbb, valueDsc->getCharSet());
 
-		const FB_UINT64 byte_offset = FB_UINT64(start) * charSet->maxBytesPerChar();
+		const FB_UINT64 byte_offset = start * charSet->maxBytesPerChar();
 		const FB_UINT64 byte_length = FB_UINT64(length) * charSet->maxBytesPerChar();
 
 		if (charSet->isMultiByte())