Re: How can I get rid of "Warning C4307: integral constant overflow"

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Tue, 5 Jun 2007 16:49:48 -0400

Message-ID:

<f44i9c$mpd$1@news.datemas.de>

_Christopher(M2M) wrote:

Microsoft Visual Studio 2005 Version 8.0.50727.762 (SP.050727-7600)

How do I get rid of "Warning C4307: '-' : integral constant overflow"
from the following macro?
   #define d_ReturnMax(I_iTypeSize)\
   ( (int64(1)<<((I_iTypeSize*8)-1))-1)

There NO warnings when done as a function:
   int64 d_ReturnMax(int64 I_iTypeSize)
   { return (1<<((I_iTypeSize*8)-1))-1;}

Test code:
   int64 L_iMaxIntSize=d_ReturnMax(sizeof(int32)); //
L_iMaxIntSize=0x000000007fffffff
   int64 L_iMaxIntSize=d_ReturnMax(sizeof(char)); //
L_iMaxIntSize=0x000000000000007f

I tried typecasting around all parts of code i.e.
int64(...)/(int64)... I give up now.
Can anyone else spot something I have missed?

Probably. One, 'int64' is compiler-specific and should be asked
about in the newsgroup dedicated to that compiler. Two, to form
a constant of a particular type you need to follow it with a certain
suffix, like 0xffL for 'long' or 0x55U for 'unsigned' (hint: int64
probably has its own dedicated suffix), do not use a "cast". Also,
shifts only work with the right argument between 0 and some
(relatively small) number. Make sure whatever '((I_iTypeSize*8)-1))'
(do you really need all those parentheses?) expands into is between
0 and the maximum allowed value (63?).

V
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