From: Jim Wilson <wilson@specifixinc.com>
To: Scott Robert Ladd <coyote@coyotegulch.com>
Cc: gcc@gcc.gnu.org
Subject: Re: 128-bit long long?
Date: Tue, 30 Mar 2004 02:10:00 -0000 [thread overview]
Message-ID: <4068C184.4050307@specifixinc.com> (raw)
In-Reply-To: <405DB46B.80208@coyotegulch.com>
Scott Robert Ladd wrote:
> On a 64-bit AMD64 architecture, GCC defines long long as 64 bits, the
> same as a long.
> Given that certain 64-bit instructions (multiply) produce 128-bit
> results, doesn't it seem logical the long long be defined as 128 bits?
Part of the reason here is historical accident. Early 64-bit targets
had to be supported via cross compilation from 32-bit hosts. Gcc
internally represents tree and rtl values as 2 HOST_WIDE_INT values.
This was before most compilers had long long support, so HOST_WIDE_INT
had to be long. Thus a 32-bit host could support at most a 64-bit
integer type. So all early 64-bit ports had to limit long long to
64-bits. This restriction was removed relatively recently, between 3.3
and 3.4. So it wasn't until 3.4 that we can have a 128-bit long long
type and still support cross compilation from a 32-bit host. However,
by now, 64-bit long long assumptions have been written into so much
software that changing it would be too painful.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com
prev parent reply other threads:[~2004-03-30 0:38 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-21 17:34 Scott Robert Ladd
2004-03-21 17:37 ` Andreas Jaeger
2004-03-21 18:02 ` Paolo Carlini
2004-03-21 20:27 ` Erik Trulsson
2004-03-21 20:52 ` Zack Weinberg
2004-03-21 21:11 ` Joseph S. Myers
2004-03-21 21:20 ` Scott Robert Ladd
2004-03-22 0:12 ` Paolo Carlini
2004-03-24 5:38 ` Richard B. Kreckel
2004-03-24 5:57 ` Paolo Carlini
2004-03-30 2:10 ` Jim Wilson [this message]
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