From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andreas Schwab <schwab@suse.de>
Date: Tue, 16 Apr 2002 20:31:02 +0000
Subject: Re: [Linux-ia64] gcc type promotion bug?
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To: linux-ia64@vger.kernel.org

Richard Hirst <rhirst@linuxcare.com> writes:

|> #include <stdio.h>
|>=20
|> int
|> main(int argc, char **argv)
|> {
|>         long a =3D 0x70000037L;
|>         float f =3D 0.01;
|>         long b =3D a + 1L/f;
|>=20
|>         printf("%lx, %lx\n", b, a + 100L);
|>         return 0;
|> }
|>=20
|>=20
|>=20
|> In the above, 1/f =3D 100, so the two numbers printed out should be the
|> same.  For me it prints out "70000080, 7000009b".  Same for gcc 2.96
|> and 3.0.3.
|>=20
|> By trying various numbers for 'a', it appears to me that it is demoting
|> 'a' to a float when evaluating 'b', thus truncating it to 24 significant
|> bits.  I thought all mixed mode arithmetic was supposed to be promoted
|> to doubles for evaluation.

No.  There are no operands of type double or long double involved, so the
ususal arithmetic conversions (6.3.1.8) choose float as the common type:

    Otherwise, if the corresponding real type of either operand is float,
    the other operand is converted, without change of type domain, to a
    type whose corresponding real type is float.

Andreas.

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Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE GmbH, Deutschherrnstr. 15-19, D-90429 N=FCrnberg
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