Bug #65485 [Com]: Cast gives different values in one way or the other

Edit report at https://bugs.php.net/bug.php?id=65485&edit=1 ID: 65485 Comment by: stephane at it-asia dot com Reported by: stephane at it-asia dot com Summary: Cast gives different values in one way or the other Status: Not a bug Type: Bug Package: *General Issues Operating System: Windows 8 & Mint Maya PHP Version: 5.4.18 Block user comment: N Private report: N New Comment: I don't find sane to see a 3948 float value going to 3947 after an int casting, I really, really don't find it sane. I don't find sane as well to see the same number ending with different value after several casts. The cast doesn't provide the same precision when it is one case, ot the other. One uses floor(), when the other uses (round). And to be honest, one is obviously right, when the other is obviously wrong. Please provide examples where the float -> string -> int value doesn't give satisfaction. Because for me, the float -> int cast NEVER gives satisfaction when there's a decimal number involved. The right way is the way giving the right solution, It is not the one giving the wrong answer for the only pleasure to match impossibility theory. In every case, please add to the documentation that the float -> int cast gives stupid results because ti tends to respect a theoric lack orp precision, when the float -> string cast tends to provide a more acceptable answer. Previous Comments: ------------------------------------------------------------------------ [2013-08-20 09:53:17] nikic@php.net I think you misunderstood how the casts work: An (int) cast rounds DOWN to the nearest integer (in all sane languages). A (string) cast just converts the float to a string representation. This representation has the precision specified with the "precision" ini setting. So what you are comparing here is a down-round ( floor($f) ) with a round-with-precision ( round($f, $prec) ). Of course the result will be different. ------------------------------------------------------------------------ [2013-08-20 09:46:50] stephane at it-asia dot com Yes I know about the imprecision and the link, this is what you say all the time here. But if you THINK about the matter, the casting algorythm is different, and this is WRONG. Other languages found solutions for that. I can't believe in 2013 PHP still cannot provide a reliable solution to make simple operation like "multiplications" and int casting. The cast algorythm for float -> string -> int is GOOD. It is ALL THE TIME. The cast algorythm for float -> int is WRONG. It is ALL THE TIME. Please implement the same solution in both sides, hence choose the good one. ------------------------------------------------------------------------ [2013-08-20 09:02:04] johannes@php.net 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://www.floating-point-gui.de/ Thank you for your interest in PHP. Casting to string will be imprecise, then doing cast to int will be imprecise again. Two imprecisions increase the difference. ------------------------------------------------------------------------ [2013-08-20 08:50:20] stephane at it-asia dot com Description: ------------ I have different value when I cast a double to int and when I cast to string before casting to int. I understand 39.48 is difficult to store in base 2. The problem is the cast algorythm is not the same if you cast a float to int or if you cast a float to string, This involves huges mistakes in accountancy software. Whatever the way you choose (float -> int or float -> string -> int ) , you should have the same result at the end. Please define the right way to process data in that case. I have the same problem with almost every machines, Windows or Debian based. Thanks ! Test script: --------------- $d = "39.48" * "100"; print("39.48 * 100 : "); var_dump ($d); $i = (int) $d; print("<br />int: "); var_dump ($i); $s = (string) $d; print("<br />string: "); var_dump ($s); $i = (int) $s; print("<br />int: "); var_dump ($i); Expected result: ---------------- same value if you cast double => int and if you cast double => string => int Actual result: -------------- 39.48 * 100 : double(3948) int: int(3947) string: string(4) "3948" int: int(3948) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=65485&edit=1