From: Lars Brinkhoff <lars@nocrew.org>
To: Warner Losh <imp@bsdimp.com>
Cc: Luther Johnson <luther.johnson@makerlisp.com>, tuhs@tuhs.org
Subject: [TUHS] Re: C history question: why is signed integer overflow UB?
Date: Sat, 16 Aug 2025 06:01:40 +0000 [thread overview]
Message-ID: <7wjz33vm7v.fsf@junk.nocrew.org> (raw)
In-Reply-To: <CANCZdfomCJ5hz0iqeYsBC32Cq_u7gNmT-RR5mPU6DwPgZh4eyA@mail.gmail.com> (Warner Losh's message of "Fri, 15 Aug 2025 12:03:46 -0600")
Warner Losh writes:
> I suspect that it was the absence of a signed right shift. In my
> Decsystem-20 OS class, one of the differences between the compiler on
> the VAX and the compiler on the '20 was that -1 >> 1 was -1 on the VAX
> and 2^35-1 on the '20.
The DEC-20 (aka PDP-10) does have a signed right shift instruction.
Apparently the compiler didn't use it.
next prev parent reply other threads:[~2025-08-16 6:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-15 17:17 [TUHS] C history question: why is signed integer overflow UB? Dan Cross
2025-08-15 17:31 ` [TUHS] " Luther Johnson
2025-08-15 17:36 ` Luther Johnson
2025-08-15 18:03 ` Warner Losh
2025-08-16 6:01 ` Lars Brinkhoff [this message]
2025-08-15 18:02 ` Nevin Liber
2025-08-15 18:25 ` Luther Johnson
2025-08-15 18:44 ` John Levine
2025-08-15 21:04 ` Douglas McIlroy
2025-08-15 21:59 ` Dave Horsfall
2025-08-15 23:58 ` Luther Johnson
2025-08-17 2:25 ` Clem Cole
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