https://www.lysator.liu.se/c/dmr-on-or.html

From decvax!harpo!npoiv!alice!research!dmr Fri Oct 22 01:04:10 1982
Subject: Operator precedence
Newsgroups: net.lang.c

The priorities of && || vs. == etc. came about in the following way.

Early C had no separate operators for & and && or | and ||.  (Got
that?)  Instead it used the notion (inherited from B and BCPL) of
"truth-value context": where a Boolean value was expected, after "if"
and "while" and so forth, the & and | operators were interpreted as &
& and || are now; in ordinary expressions, the bitwise
interpretations were used.  It worked out pretty well, but was hard
to explain. (There was the notion of "top-level operators" in a
truth-value context.)

The precedence of & and | were as they are now.

Primarily at the urging of Alan Snyder, the && and || operators were
added.  This successfully separated the concepts of bitwise
operations and short-circuit Boolean evaluation.  However, I had cold
feet about the precedence problems.  For example, there were lots of
programs with things like

        if (a==b & c==d) ...

In retrospect it would have been better to go ahead and change the
precedence of & to higher than ==,  but it seemed safer just to split
& and && without moving & past an existing operator.  (After all, we
had several hundred kilobytes of source code, and maybe 3
installations....)

Dennis Ritchie