Promotion of integral types

Tom Kelly tom at hcrvx1.UUCP
Fri Sep 26 22:23:39 AEST 1986

In article <271 at myrias.UUCP> cmt at 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:


	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

Tom Kelly  (416) 922-1937
Human Computing Resources Corp.
{utzoo, ihnp4, decvax}!hcr!hcrvx1!tom

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