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Date: Mon, 30 Aug 2004 21:24:40 +0100
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Subject: Re: [PHP-DEV] [PATCH] zend_operators DVAL_TO_LVAL fix
From: jorton@redhat.com (Joe Orton)

On Mon, Aug 30, 2004 at 12:32:59PM -0700, Andi Gutmans wrote:
> Hi Joe,
> 
> It seems like your patch doesn't really fix anything. How is rounding to 
> LONG_MAX/LONG_MIN any better?

The C standard says that when converting a double to a long, if the
integral part of the double is outside the range which can be
represented by a long, the conversion has undefined behaviour.

#define DVAL_TO_LVAL(d, l) (l) = (d) > LONG_MAX ? (unsigned long) (d) : (long) (d)

where d is a double and l is a long: so this has undefined behaviour for
values of d greater than ULONG_MAX or smaller than LONG_MIN.

#define DVAL_TO_LVAL(d, l) do {                 \
        if ((d) > LONG_MAX) {                   \
                l = LONG_MAX;                   \
        } else if ((d) < LONG_MIN) {            \
                l = LONG_MIN;                   \
        } else {                                \
                l = (d);                        \
        }                                       \
} while (0)

has well-defined behaviour for all values of 'd', since it will never
attempt to assign a value to 'l' which cannot be represented by a long.

> Maybe you can explain in more detail what this gcc bug you are hitting is?

It seems to be an IA64-specific optimisation bug, it's really incidental
to the fact that the current code is dubious.  GCC evaluates the
expression as either 0 or LONG_MIN if d is negative, depending on -O
level.  (Which is fairly nasty)

joe