http://d.puremagic.com/issues/show_bug.cgi?id=4835

           Summary: DMD should warn about integer overflow in computed
                    constant
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: lars.holowko@gmail.com


--- Comment #0 from Lars Holowko <lars.holowko@gmail.com> 2010-09-07 10:09:23 PDT ---
I got bitten by this when I wanted to create a 6GB large file to test 64 bit support in std.stdio with dmd 2.048.


The output of:


import std.stdio;

void main(string args[])
{
    long l_dangerous = 1024 * 1024 * 1024 * 6;
    writefln("l_dangerous = 0x%x", l_dangerous);
    writefln("l_dangerous = %s", l_dangerous);

    long l_ok = 1024 * 1024 * 1024 * 6L;
    writefln("l_ok = 0x%x", l_ok);
    writefln("l_ok = %s", l_ok);
    return;
}

is

l_dangerous = 0xffffffff80000000
l_dangerous = -2147483648
l_ok = 0x180000000
l_ok = 6442450944


dmd 2.048 did not issue a warning about the integer overflow (neither with or
without -w)

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #1 from bearophile_hugs@eml.cc 2010-09-07 12:39:13 PDT ---
I'm asking for overflow detection for years (both at compile-time and
run-time).

Again here the C language is better than the D language:

// C code
#include "stdio.h"
int main() {
    long long x = 1024 * 1024 * 1024 * 6;
    printf("%lld\n", x);
    return 0;
}


GCC 4.3.4 gives:
prog.c: In function ‘main’:
prog.c:3: warning: integer overflow in expression

D compiler is not _practical_ enough yet.

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Brad Roberts <braddr@puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Platform|x86_64                      |x86


--- Comment #2 from Brad Roberts <braddr@puremagic.com> 2011-02-06 15:38:57 PST ---
Mass migration of bugs marked as x86-64 to just x86.  The platform run on isn't what's relevant, it's if the app is a 32 or 64 bit app.

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--- Comment #3 from bearophile_hugs@eml.cc 2013-03-26 11:27:23 PDT ---
An example in Go language:


package main
func main() {
    var x uint32 = 1 << 40
    var y = 1024 * 1024 * 1024 * 6
}


The Go compiler gives the errors:

test.go:3: constant 1099511627776 overflows uint32 test.go:4: constant 6442450944 overflows int

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--- Comment #4 from bearophile_hugs@eml.cc 2013-03-26 11:29:45 PDT ---
Another example in Go:


package main
func main() {
    var x uint64 = 1 << 90
}


The Go compiler gives the error:

test.go:3: constant 1237940039285380274899124224 overflows uint64

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Luís Marques <luismarques@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luismarques@gmail.com


--- Comment #5 from Luís Marques <luismarques@gmail.com> 2013-03-26 11:50:04 PDT ---
(In reply to comment #4)

For completeness, it also does not have a problem (like in your example) where
the initializer of the 64-bit variable is initialized with (what is not
obvious) a folded and truncated 32-bit int:

    var x uint64 = 4 * 1024 * 1024 * 1024;
    // x is now 4294967296, not 0.

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com


--- Comment #6 from Walter Bright <bugzilla@digitalmars.com> 2013-03-26 13:14:08 PDT ---
uint foo() {
    uint x = 1 << 40;
    return 1 << 90;
}

gives:

foo2.d(3): Error: shift by 40 is outside the range 0..31
foo2.d(4): Error: shift by 90 is outside the range 0..31

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--- Comment #7 from bearophile_hugs@eml.cc 2013-03-26 15:13:56 PDT ---
(In reply to comment #6)
> uint foo() {
>     uint x = 1 << 40;
>     return 1 << 90;
> }
> 
> gives:
> 
> foo2.d(3): Error: shift by 40 is outside the range 0..31
> foo2.d(4): Error: shift by 90 is outside the range 0..31

I was aware of that. I have added the 1<<90 example to show the peculiar error message given by Go, that contains 1237940039285380274899124224, that is larger than a ulong.

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--- Comment #8 from Walter Bright <bugzilla@digitalmars.com> 2013-03-26 19:06:55 PDT ---
https://github.com/D-Programming-Language/dmd/pull/1803

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--- Comment #9 from bearophile_hugs@eml.cc 2013-03-26 19:45:01 PDT ---
(In reply to comment #8)
> https://github.com/D-Programming-Language/dmd/pull/1803

An error, even :-) So the issue name should be updated.

Thank you Walter. Let's see how this patch goes.

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