in reply to substr outside of string? (Updated: Fixed in later builds.)

$a x= 2**31; creates an empty string, so there's an overflow, so something is using an I32 or IV when it should be using a STRLEN. (If this error occurs on a 64-bit build, then it's an I32 being used.) Any substring starting at a position later than zero therefore starts outside of the string.

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Re^2: substr outside of string?
by ikegami (Patriarch) on Jun 16, 2013 at 16:04 UTC 
    PP(pp_repeat)
{
    ...
    IV count;                                               <----
    ...

    if (SvIOKp(sv)) {
        if (SvUOK(sv)) {
            const UV uv = SvUV_nomg(sv);
            if (uv > IV_MAX)
                count = IV_MAX; /* The best we can do? */   <---- WTF
            else
                count = uv;
        } else {
            const IV iv = SvIV_nomg(sv);
            if (iv < 0)
                count = 0;
            else
                count = iv;
        }
    }
    else if (SvNOKp(sv)) {
        const NV nv = SvNV_nomg(sv);
        if (nv < 0.0)
            count = 0;
        else
            count = (IV)nv;
    }
    else
        count = SvIV_nomg(sv);

    ...
}

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Re^2: substr outside of string?
by BrowserUk (Patriarch) on Jun 16, 2013 at 16:04 UTC
    $a x= 2**31; creates an empty string,

    Look again: 

    C:\test>perl
$a = chr(0); $a x= 2**31;
print length $a;
substr( $a, 0, 2**16 ) =~ tr[\0][\1];
substr( $a, 2**16, 2**16 ) =~ tr[\0][\1];
^Z
substr outside of string at - line 3.
2147483648

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    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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[d/l]
      On systems with 32-bit IVs, one gets zero. I guess there are two problems, then.
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