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NQP converts large integers to floats when it shouldn't/doesn't need to #363

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coke opened this issue May 29, 2017 · 3 comments · Fixed by #518
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NQP converts large integers to floats when it shouldn't/doesn't need to #363

coke opened this issue May 29, 2017 · 3 comments · Fixed by #518

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@coke
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coke commented May 29, 2017 •
edited

Originally posted in https://rt.perl.org/Ticket/Display.html?id=131385 by ddgreen @ gmail.com

So `nqp-m -e 'say(100000000000000009)'` prints `100000000000000016`.

See https://irclog.perlgeek.de/perl6-dev/2017-05-27#i_14646898 for some discussion with jnthn.
@MasterDuke17 MasterDuke17 mentioned this issue Aug 1, 2018
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zoffixznet added a commit to rakudo/rakudo that referenced this issue Aug 1, 2018
@zoffixznet
Fix wrong math with largish Ints
fec1bd7 
Fixes R#2157 #2157

The cause of the bug is NQP apparently uses doubles to handle its
ints[^1]. 2**52 is the limit under which every number is representable
in a double, which is why when we bumped up[^2] the point at which we
switched to bigints in Rakudo to be over that limit, we brought in the
NQP's limitation into Perl 6 land.

Fix by dialing down the switch to bigint to occur before we go over the
2**52 limit. The NQP Issue[^1] will resolve the problem in NQP land and
once that's done, I presume we can bump up the limit in rakudo once again.

[1] N#363 Raku/nqp#363
[2] b61b3c7
@zoffixznet
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zoffixznet commented Aug 1, 2018 •
edited

FWIW, this problem had impacted Perl 6 numerics too (R#2157)

In rakudo/rakudo@fec1bd74f9 and rakudo/rakudo@8e2c70fa15, I avoided that issue by going under the 2**52 limit under which every integer is representable in double.

Once this issue is fixed, I think we can bump up that limit in Rakudo again.

@tisonkun
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tisonkun commented Aug 2, 2018

FYI,

nqp -e 'say(0x100000000000000009)' prints `9`

is it relevant?

@tisonkun
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tisonkun commented Aug 2, 2018

Here might be code snip

https://github.com/MoarVM/MoarVM/blob/4d9829c061d35646d045a1d90d27337b3471b89d/src/core/coerce.c#L349-L420

could we auto-detect if we need bigint instead of int in nqp::radix?

@MasterDuke17 MasterDuke17 mentioned this issue Feb 5, 2019
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@p6rt p6rt mentioned this issue Jan 5, 2020
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Make variables and ops default to int MasterDuke17/nqp
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@coke @zoffixznet @tisonkun