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Why? console.log(parseFloat(1024) + parseFloat(300.86)); = 1324.8600000000001 #3542

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iceopen opened this issue Oct 27, 2015 · 3 comments
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@iceopen
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iceopen commented Oct 27, 2015

console.log(parseFloat(1024) + parseFloat(300.86));
console.log(parseFloat(100) + parseFloat(100.86));
console.log(parseFloat(1024) + parseFloat(200.78));
console.log(parseFloat(400) + parseFloat(200.86));
var tol = parseFloat(1024) + parseFloat(300.86);
console.log(tol);

1324.8600000000001
200.86
1224.78
600.86
1324.8600000000001

@mscdex mscdex added the question Issues that look for answers. label Oct 27, 2015
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mscdex commented Oct 27, 2015

Welcome to the world of floating point math. There are lots of articles that describe how floating point in general works. You might start with the answers from this stackoverflow question.

@iceopen
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iceopen commented Oct 27, 2015

I tested the pull 3 programming languages:
Java:1324.8600000000001
Node:1324.8600000000001
PHP:1324.86

@bnoordhuis
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Closing, not a bug. Like @mscdex said, that's how floating point values work; 1324.86 is a value that cannot be exactly represented in a binary IEEE-754 double.

PHP has the same issue by the way, it's just that the way it prints floating point numbers by default doesn't show it:

$ php -r 'printf("%.16f\n", 1024.0 + 300.86);'
1324.8600000000001273

One language that does get it right is perl6:

$ perl6 -e 'printf "%.16f\n", 1024.0 + 300.86'
1324.8600000000000000

That's because it represents the number as a nominator/denominator rational:

$ perl6 -e 'print "{(1024.0 + 300.86).nude}\n"'
66243 50

The more you know, right?

@bnoordhuis bnoordhuis added the invalid Issues and PRs that are invalid. label Oct 27, 2015
ryzokuken added a commit to ryzokuken/node that referenced this issue Mar 8, 2018
Rename the test appropriately alongside mentioning the subsystem
Also, make a few basic changes to make sure the test conforms
to the standard test structure

Refs: nodejs#19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
BridgeAR pushed a commit to BridgeAR/node that referenced this issue Mar 11, 2018
Rename the tests appropriately alongside mentioning the subsystem.
Also, make a few basic changes to make sure the test conforms
to the standard test structure.

This renames:
- test-regress-nodejsGH-1531
- test-regress-nodejsGH-2245
- test-regress-nodejsGH-3238
- test-regress-nodejsGH-3542
- test-regress-nodejsGH-3739
- test-regress-nodejsGH-4256

PR-URL: nodejs#19212
Refs: nodejs#19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
targos pushed a commit that referenced this issue Mar 17, 2018
Rename the tests appropriately alongside mentioning the subsystem.
Also, make a few basic changes to make sure the test conforms
to the standard test structure.

This renames:
- test-regress-GH-1531
- test-regress-GH-2245
- test-regress-GH-3238
- test-regress-GH-3542
- test-regress-GH-3739
- test-regress-GH-4256

PR-URL: #19212
Refs: #19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
MylesBorins pushed a commit that referenced this issue Mar 20, 2018
Rename the tests appropriately alongside mentioning the subsystem.
Also, make a few basic changes to make sure the test conforms
to the standard test structure.

This renames:
- test-regress-GH-1531
- test-regress-GH-2245
- test-regress-GH-3238
- test-regress-GH-3542
- test-regress-GH-3739
- test-regress-GH-4256

PR-URL: #19212
Refs: #19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
MayaLekova pushed a commit to MayaLekova/node that referenced this issue May 8, 2018
Rename the tests appropriately alongside mentioning the subsystem.
Also, make a few basic changes to make sure the test conforms
to the standard test structure.

This renames:
- test-regress-nodejsGH-1531
- test-regress-nodejsGH-2245
- test-regress-nodejsGH-3238
- test-regress-nodejsGH-3542
- test-regress-nodejsGH-3739
- test-regress-nodejsGH-4256

PR-URL: nodejs#19212
Refs: nodejs#19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
BethGriggs pushed a commit that referenced this issue Oct 2, 2018
Rename the tests appropriately alongside mentioning the subsystem.
Also, make a few basic changes to make sure the test conforms
to the standard test structure.

This renames:
- test-regress-GH-1531
- test-regress-GH-2245
- test-regress-GH-3238
- test-regress-GH-3542
- test-regress-GH-3739
- test-regress-GH-4256

PR-URL: #19212
Refs: #19105
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
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