On: Dennis Ritchie’s first C compiler (c. 1972)

[_kst_]

> It makes sense long would have needed a comment.

I think you misunderstood. There's no explanatory comment. The "long" keyword is commented out, meaning that it was planned but not yet implemented.

    ...
            init("int", 0);
            init("char", 1);
            init("float", 2);
            init("double", 3);
    /*      init("long", 4);  */
            init("auto", 5);
            init("extern", 6);
            init("static", 7);
    ...

[hakanai → _kst_]

Hmm, given its position in that sequence, it looks like it means a floating-point type larger than a double.