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From: tom@hcrvx1.UUCP (Tom Kelly)
Newsgroups: net.lang.c
Subject: Re: Promotion of integral types
Message-ID: <1405@hcrvx1.UUCP>
Date: Fri, 26-Sep-86 08:23:39 EDT
Article-I.D.: hcrvx1.1405
Posted: Fri Sep 26 08:23:39 1986
Date-Received: Sat, 27-Sep-86 00:23:23 EDT
References: <3594@brl-smoke.ARPA> <1219@drutx.UUCP> <2233@gitpyr.UUCP> <547@chinet.UUCP> <3422@umcp-cs.UUCP> <271@myrias.UUCP>
Reply-To: tom@hcrvx1.UUCP (Tom Kelly)
Organization: Human Computing Resources, Toronto
Lines: 34
Summary: 

In article <271@myrias.UUCP> cmt@myrias.UUCP (Chris Thomson) writes:

> ...  The ANSI Draft (1986.07.09 version) says
>very clearly that unsigned char and unsigned short are promoted to int,
>since the values can all be represented in an int (assuming sizeof(int)
>is greater than sizeof(short), which is usually true).
>
>What to do?  Frankly, I prefer the ANSI approach, but it does represent a
>silent change from what H&S (and Chris Torek) perceive to be standard
>practice.  For some reason, it is not flagged as such in the rationale
>document; it isn't even discussed there.

This change was the subject of long and hard investigation and
debate in the ANSI C (X3J11) committee.  It is a quiet change
from common practice in (for example) PCC-based compilers, but
there are other implementations that do promote unsigned
char and unsigned short to int.  The decision was not made lightly -
the debate went on for at least a year.

The issue is discussed at length in the Rationale (86-099 7 July 1986),
in 3.2 Conversions (pp. 32-33).  In particular, on p 33:

			QUIET CHANGE

	A program that depends upon unsigned preserving arithmetic
	conversions will behave differently, probably without
	complaint.  This is considered the most serious semantic
	change made by the Committee to a widespread current
	practice.


Tom Kelly  (416) 922-1937
Human Computing Resources Corp.
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