* patch by Bart B to fix fpc_val_smallint_shortstr similiar to #39406, resolves #39528

rtl/inc/sstrings.inc

@@ -1504,17 +1504,22 @@ end;
 
   Function fpc_val_smallint_shortstr(Const S: ShortString; out Code: ValSInt): SmallInt; [public, alias:'FPC_VAL_SMALLINT_SHORTSTR']; compilerproc;
 
-  var  u, temp, prev, maxprevvalue, maxnewvalue : word;
+  var  u, temp, prev, maxprevvalue : word;
        base : byte;
        negative : boolean;
-
-  const maxlongint=longword($7fffffff);
-        maxlongword=longword($ffffffff);
-
+       UnsignedUpperLimit: ValUInt;
+  const
+    ValueArray : array['0'..'f'] of byte = (0,1,2,3,4,5,6,7,8,9,$FF,$FF,$FF,$FF,$FF,$FF,$FF,10,11,12,13,14,15,
+                                            $FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,
+                                            10,11,12,13,14,15);
   begin
     fpc_val_smallint_shortstr := 0;
     Temp:=0;
     Code:=InitVal(s,negative,base);
+    if (base=10) or negative then
+      UnsignedUpperLimit := Word(High(SmallInt))+Ord(negative)
+    else
+      UnsignedUpperLimit := High(Word);
     if Code>length(s) then
      exit;
     if (s[Code]=#0) then
@@ -1523,27 +1528,22 @@ end;
           Code:=0;
         exit;
       end;
-    maxprevvalue := maxlongword div base;
-    if (base = 10) then
-      maxnewvalue := maxlongint + ord(negative)
-    else
-      maxnewvalue := maxlongword;
+    maxprevvalue := High(Word) div base;
 
     while Code<=Length(s) do
      begin
-       case s[Code] of
-         '0'..'9' : u:=Ord(S[Code])-Ord('0');
-         'A'..'F' : u:=Ord(S[Code])-(Ord('A')-10);
-         'a'..'f' : u:=Ord(S[Code])-(Ord('a')-10);
+       u:=16;
+       case s[code] of
+         '0'..'f' : u:=ValueArray[S[Code]];
          #0 : break;
        else
-        u:=16;
+         ;
        end;
        Prev:=Temp;
        Temp:=Temp*longword(base);
-     If (u >= base) or
-        (longword(maxnewvalue-u) < temp) or
-        (prev > maxprevvalue) Then
+       If (u >= base) or
+        (prev > maxPrevValue) or
+        ((Temp)>(UnsignedUpperLimit-u)) Then
        Begin
          fpc_val_smallint_shortstr := 0;
          Exit
@@ -1552,7 +1552,7 @@ end;
        inc(code);
      end;
     code:=0;
-    fpc_val_smallint_shortstr:=longint(Temp);
+    fpc_val_smallint_shortstr:=SmallInt(Temp);
     If Negative Then
       fpc_val_smallint_shortstr:=-fpc_val_smallint_shortstr;
   end;