Wise Monks,

I am trying to translate some JS code into Perl. The problem is that I think said JS code does not handle well overflows when doing a left shift and it calculates the result (let's say a checksum) wrongly. But this is now the result and I must emulate that result in my Perl translation. I can not fix the JS code, it is not mine. Question is: how?

Here is the gist of it assuming a 64bit Linux console with node.js installed and bash:

node -e 'console.log(1<<30);'
1073741824
echo $((1<<30))
1073741824 # same result
perl -e 'print 1<<30, "\n"'
1073741824 # same result

node -e 'console.log(1<<31);'
-2147483648 # overflow in 32bit!
echo $((1<<31))
2147483648 # correct result
perl -e 'print 1<<31, "\n"'
2147483648 # same result

# to obtain the overflow in bash
echo $((1<<63))
-9223372036854775808 # overflow in 64bit
# still perl does not
perl -e 'print 1<<63, "\n"'
9223372036854775808
perl -e 'print 1<<64, "\n"'
0 # gotcha!

# this is when I realised the problem:
node -e 'console.log(1169367104<<5);'
-1234958336
echo $((1169367104<<5))
37419747328
perl -e 'print 1169367104<<5, "\n"'
37419747328 # same result

[download]

(note: if you don't have node.js open your browser, open its 'web developer tools', go to tab 'console' and just paste that bit of harmless js code

So, I am asking: how can I make perl print -1234958336 when left-shifting 1169367104<<5 ?

use Test::More;
is(1169367104<<5, -1234958336, "simulated JS 32bit shift.");
done_testing;

[download]

bw, bliako

Edit: I have asked a more general question about JS/C/Perl integer overflows at https://stackoverflow.com/questions/77584450/emulate-javascripts-32bit-signed-integer-arithmetic-to-c-or-perl-some-discr

In reply to Trying to translate overflowing JS code to Perl by bliako

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