#50824 [Opn->Bgs]: modulus (mod) returns wrong value

ID: 50824 Updated by: rasmus@php.net Reported By: jancha at trave dot lv -Status: Open +Status: Bogus Bug Type: Math related Operating System: Gentoo PHP Version: 5.2.12 New Comment: Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. If you would like to know more about "floats" and what IEEE 754 is, read this: http://docs.sun.com/source/806-3568/ncg_goldberg.html Thank you for your interest in PHP. 72.6 * 100 is not exactly 7260 Previous Comments: ------------------------------------------------------------------------ [2010-01-22 14:46:10] jancha at trave dot lv Description: ------------ We came accorss following case: <?php echo 72.6 * 100 % 100; You would expect: 60 But you get: 59 We did further analysis and got following results: [OK] 72.0:0 [FAIL] 72.1:9 [OK] 72.2:20 [OK] 72.3:30 [OK] 72.4:40 [OK] 72.5:50 [FAIL] 72.6:59 [OK] 72.7:70 [OK] 72.8:80 [OK] 72.9:90 That makes us think that bug happens, if last digit is either 1 or 6. Also, according to manual, operands of modulus are converted to integers by stripping decimal part away - in our case that is not reason, as 72.6 * 100 = 7260 (float). And conversion to int should result with 7260. Reproduce code: --------------- <?php echo 72.6 * 100 % 100; Expected result: ---------------- 60 Actual result: -------------- 59 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=50824&edit=1