Bug #64760 [Com]: var_export() does not use full precision for floating-point numbers

Edit report at https://bugs.php.net/bug.php?id=64760&edit=1 ID: 64760 Comment by: whatthejeff@php.net Reported by: cf0hay at gmail dot com Summary: var_export() does not use full precision for floating-point numbers Status: Closed Type: Bug Package: Variables related Operating System: Linux 64bit (PHP 64bit too) PHP Version: 5.4.14 Assigned To: yohgaki Block user comment: N Private report: N New Comment: Corrected link: https://github.com/php/php-src/pull/525 Previous Comments: ------------------------------------------------------------------------ [2013-11-14 03:07:47] whatthejeff@php.net This change can break tests on some systems. See https://github.com/php/php-src/pull/525. ------------------------------------------------------------------------ [2013-10-29 11:29:37] yohgaki@php.net Committed fix, but not auto closed. Closing 3cf2682083fc1c8635b02c4cf77bdf12c5e5da35 ------------------------------------------------------------------------ [2013-10-23 09:09:26] yohgaki@php.net The difference came from var_export() ------------------------------------------------------- case IS_DOUBLE: tmp_len = spprintf(&tmp_str, 0,"%.*H", (int) EG(precision), Z_DVAL_PP(struc)); smart_str_appendl(buf, tmp_str, tmp_len); efree(tmp_str); break;------------------------------------------------------- serialize() ------------------------------------------------------- case IS_DOUBLE: { char *s; smart_str_appendl(buf, "d:", 2); s = (char *) safe_emalloc(PG(serialize_precision), 1, MAX_LENGTH_OF_DOUBLE + 1); php_gcvt(Z_DVAL_P(struc), PG(serialize_precision), '.', 'E', s); smart_str_appends(buf, s); smart_str_appendc(buf, ';'); efree(s); return; } ------------------------------------------------------- var_export() uses precision=14 while serialize() uses precision=17 by default. ------- [yohgaki@dev php-5.5]$ php -e precision=17 scr.php error of serialize(): 0 error of var_export(): 0 ------- Since var_export() is better to behave like serialize(), var_export() is better to use PG(serialize_precision) instead of PG(precision). ------------------------------------------------------------------------ [2013-05-02 12:12:44] cf0hay at gmail dot com Description: ------------ var_export() truncates floating-point precision. serialize() does not have the same problem. Test script: --------------- <?php $a = microtime(true); echo "error of serialize(): "; var_export($a - unserialize(serialize($a))); //This returns 0. echo "\n"; echo "error of var_export(): "; eval('$b = '.var_export($a,true).';'); var_export($a - $b); //Almost never 0. echo "\n"; Expected result: ---------------- Exporting a floating-point value should generate enough digits to prevent precision loss. The script above should always return 0 on the second case. Actual result: -------------- The difference between the original floating point value and the one exported differs. The error is about 15 magnitude lower than the magnitude of the value itself. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=64760&edit=1