Re^3: Trying to translate overflowing JS code to Perl

I believe you can do the complete calculation without conversion and just at the end downgrade to 32 bit and convert to signed. The following should work:

sub calc_32bit_signed( $value ) {
    return unpack( "l", pack "L", ($value & 0xffffffff)))
}

...

say calc_32bit_signed( $n << 6 );
say calc_32bit_signed( $n + 2 );
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Re^4: Trying to translate overflowing JS code to Perl by syphilis (Archbishop) on Nov 29, 2023 at 11:42 UTC
`return unpack( "l", pack "L", ($value & 0xffffffff)))` For which finite numeric values do any of the following 3 renditions differ: `say unpack( "l", pack "L", ($value & 0xffffffff)); say unpack( "l", pack "L", ($value)); say unpack( "l", pack "l", ($value));` [download] Sorry ... I'm not trying to be critical ... not even nitpicking ... but I haven't found any such values, and I'm genuinely curious as to whether they exist.) Cheers, Rob	[reply] [d/l] [select]
Re^5: Trying to translate overflowing JS code to Perl by Corion (Patriarch) on Nov 29, 2023 at 13:22 UTC
Yeah - I wasn't sure either. Reconsidering, I think `pack "L"` and `pack "l"` both truncate the value to 32 bits already, so masking out higher bits does not make a difference.	[reply] [d/l] [select]
Re^4: Trying to translate overflowing JS code to Perl by bliako (Abbot) on Nov 30, 2023 at 18:00 UTC
I don't think that will work, for example consider something like `($value << 6) + length($value)`. So if the first part overflows in JS then it is necessary to overflow (the first part) in Perl too. Simulating the overflow for the sum would not do. At the moment I am running JS code via shelling out to node.js and that works just fine. I was hoping that there would be a module like Math::BigInt where you specify the number of bits or something like `use smallint;` But now, come to think of it, perhaps a new module could consist of only overloading arithmetic operators. Let me see if I can whip up something based on your pack receipe. Edit: see Re: Trying to translate overflowing JS code to Perl with working code for this.	[reply] [d/l] [select]