Why is shifting too far undefined behvaior?

From	Philipp Klaus Krause <pkk@spth.de>
Newsgroups	comp.std.c
Subject	Why is shifting too far undefined behvaior?
Date	2021-09-21 13:09 +0200
Message-ID	<siceh0$1lm$1@solani.org> (permalink)

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Looking at the C23 draft N2596, section J.2 (but this AFAIK has been the
same forever), we see that there is undefined behavior, when "An
expression is shifted by a negative number or by an amount greater than
or equal to the width of the promoted expression (6.5.7)." or "An
expression having signed promoted type is left-shifted and either the
value of the expression is negative or the result of shifting would not
be representable in the promoted type (6.5.7)."

Does anyone know why this was made undefined (as opposed to yielding an
unspecified value)? The C99 rationale doesn't mention anything.

The only idea that comes to my mind is that it would be to allow
implementations to trap at runtime when shifting too far, which might
help with debugging.

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Why is shifting too far undefined behvaior? Philipp Klaus Krause <pkk@spth.de> - 2021-09-21 13:09 +0200
  Re: Why is shifting too far undefined behvaior? Ike Naar <ike@faeroes.freeshell.org> - 2021-09-21 11:33 +0000
    Re: Why is shifting too far undefined behvaior? Richard Kettlewell <invalid@invalid.invalid> - 2021-09-21 12:47 +0100
  Re: Why is shifting too far undefined behvaior? Richard Damon <Richard@Damon-Family.org> - 2021-09-21 08:29 -0400
    Re: Why is shifting too far undefined behvaior? Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-22 01:17 +0000
      Re: Why is shifting too far undefined behvaior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-21 19:05 -0700
        Re: Why is shifting too far undefined behvaior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-22 00:02 -0400
          Re: Why is shifting too far undefined behvaior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-21 21:12 -0700
            Re: Why is shifting too far undefined behvaior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-22 09:42 -0400
          Re: Why is shifting too far undefined behvaior? Richard Damon <Richard@Damon-Family.org> - 2021-09-22 07:08 -0400
            Re: Why is shifting too far undefined behvaior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-22 09:42 -0400
              Re: Why is shifting too far undefined behvaior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-23 12:18 -0400
          Re: Why is shifting too far undefined behvaior? Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-23 11:10 +0000
            Re: Why is shifting too far undefined behvaior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-23 12:22 -0400
        Re: Why is shifting too far undefined behvaior? Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-23 11:08 +0000
  Re: Why is shifting too far undefined behvaior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-21 11:01 -0700
    Re: Why is shifting too far undefined behvaior? Philipp Klaus Krause <pkk@spth.de> - 2021-09-21 20:12 +0200
  Re: Why is shifting too far undefined behvaior? Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-22 01:13 +0000
  Re: Why is shifting too far undefined behvaior? David Brown <david.brown@hesbynett.no> - 2021-09-22 14:25 +0200
    Re: Why is shifting too far undefined behvaior? Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-23 11:17 +0000
  Re: Why is shifting too far undefined behvaior? Tim Rentsch <txr@shamko.com> - 2021-10-09 04:27 -0700

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