Fixed #5771 (false positive: (warning) When using 'char' variables in bit operations, sign extension can generate unexpected results.)

lib/checkother.cpp

@@ -168,6 +168,21 @@ static bool isOppositeCond(const Token * const cond1, const Token * const cond2,
             (comp1 == ">=" && comp2 == "<"));
 }
 
+static bool isPossibleCast(const Token * const startPar)
+{
+    if (!Token::Match(startPar, "( %type%"))
+        return false;
+    const Token *tok;
+    for (tok = startPar->tokAt(2); tok; tok = tok->next()) {
+        if (tok->str() == ")")
+            return true;
+        if (tok->varId()>0)
+            return false;
+        if (!Token::Match(tok,"%type%|*|&"))
+            return false;
+    }
+    return tok != nullptr;
+}
 
 //----------------------------------------------------------------------------------
 // The return value of fgetc(), getc(), ungetc(), getchar() etc. is an integer value.
@@ -2104,6 +2119,10 @@ void CheckOther::checkCharVariable()
                 else
                     continue;
 
+                // (x) & y => if x is a possible type then assume & is a address-of operator
+                if (Token::simpleMatch(tok->previous(), ") &") && isPossibleCast(tok->linkAt(-1)))
+                    continue;
+
                 // it's ok with a bitwise and where the other operand is 0xff or less..
                 if (tok->str() == "&" && tok2 && tok2->isNumber() && MathLib::isGreater("0x100", tok2->str()))
                     continue;

test/testcharvar.cpp

@@ -39,6 +39,7 @@ private:
         TEST_CASE(bitop1);
         TEST_CASE(bitop2);
         TEST_CASE(bitop3);
+        TEST_CASE(bitop4); // (long)&c
         TEST_CASE(return1);
         TEST_CASE(assignChar);
         TEST_CASE(and03);
@@ -160,6 +161,15 @@ private:
         ASSERT_EQUALS("[test.cpp:2]: (warning) When using 'char' variables in bit operations, sign extension can generate unexpected results.\n", errout.str());
     }
 
+    void bitop4() {
+        check("long f(char c) {\n"
+              "  long a;\n"
+              "  a = (long)&c;\n"
+              "  return a;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void return1() {
         check("void foo()\n"
               "{\n"