Bug #74221 [NEW]: Float precision is altered when encoding to JSON for floats 0.99... and under

From: bryn at imgur dot com Operating system: Ubuntu 16.04.2 LTS PHP version: 7.1.2 Package: JSON related Bug Type: Bug Bug description:Float precision is altered when encoding to JSON for floats 0.99... and under Description: ------------ The change to using serialize_precision in json_encode() may have had some side affects. Floating point numbers under 1.0 get a different precision than other floating point numbers and the precision for those numbers can be unpredictable. I noticed that var_export() is behaving the in the same way, but that is far less critical because it's not used as a data exchange format. At the moment, I have a single workaround for a single case - When encoding a JSON object only dealing with the exact same precision values, setting serialize_precision to 2 gives the expected result. That won't work for objects with mixed precision though. Test script: --------------- <?php # Getting the precision on the cli seems to change it. # Before these two lines were added, I was getting 53 points of precision. # After, it adhered to the value for serialize_precision and stayed there. #print 'Precision is set to '.ini_get('precision').PHP_EOL; #print 'Serialize Precision is set to '.ini_get('serialize_precision').PHP_EOL; $data = array( 0.35, (float)0.35, round(0.35, 2), 0.15, 1.25, 1.23, 1.0, 0.9, 4, ); print 'var_export: '.PHP_EOL.var_export($data, 1).PHP_EOL; print 'json_encode: '.PHP_EOL.json_encode($data, JSON_PRESERVE_ZERO_FRACTION).PHP_EOL; print 'print_r'.PHP_EOL; print_r($data); Expected result: ---------------- var_export: array ( 0 => 0.35, 1 => 0.35, 2 => 0.35, 3 => 0.15, 4 => 1.25, 5 => 1.23, 6 => 1.0, 7 => 0.9, 8 => 4, ) json_encode: [0.35,0.35,0.35,0.15,1.25,1.23,1.0,0.9,4] print_r Array ( [0] => 0.35 [1] => 0.35 [2] => 0.35 [3] => 0.15 [4] => 1.25 [5] => 1.23 [6] => 1 [7] => 0.9 [8] => 4 ) Actual result: -------------- var_export: array ( 0 => 0.34999999999999997779553950749686919152736663818359375, 1 => 0.34999999999999997779553950749686919152736663818359375, 2 => 0.34999999999999997779553950749686919152736663818359375, 3 => 0.1499999999999999944488848768742172978818416595458984375, 4 => 1.25, 5 => 1.229999999999999982236431605997495353221893310546875, 6 => 1.0, 7 => 0.90000000000000002220446049250313080847263336181640625, 8 => 4, ) json_encode: [0.34999999999999997779553950749686919152736663818359375,0.34999999999999997779553950749686919152736663818359375,0.34999999999999997779553950749686919152736663818359375,0.1499999999999999944488848768742172978818416595458984375,1.25,1.229999999999999982236431605997495353221893310546875,1.0,0.90000000000000002220446049250313080847263336181640625,4] print_r Array ( [0] => 0.35 [1] => 0.35 [2] => 0.35 [3] => 0.15 [4] => 1.25 [5] => 1.23 [6] => 1 [7] => 0.9 [8] => 4 ) -- Edit bug report at https://bugs.php.net/bug.php?id=74221&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=74221&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=74221&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=74221&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=74221&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=74221&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=74221&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=74221&r=needscript Try newer version: https://bugs.php.net/fix.php?id=74221&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=74221&r=support Expected behavior: https://bugs.php.net/fix.php?id=74221&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=74221&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=74221&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=74221&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=74221&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=74221&r=dst IIS Stability: https://bugs.php.net/fix.php?id=74221&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=74221&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=74221&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=74221&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=74221&r=mysqlcfg