#47168 [Opn->Asn]: printf of floating point variable prints maximum of 40 decimal places

ID: 47168 Updated by: jani@php.net Reported By: exploringbinary at gmail dot com -Status: Open +Status: Assigned Bug Type: Math related -Operating System: Windows +Operating System: * -PHP Version: 5.2.8 +PHP Version: 5.2.9 Assigned To: rasmus Previous Comments: ------------------------------------------------------------------------ [2009-04-30 03:48:24] rasmus@php.net There are a couple of other places that need to be changed. I have a patch but I haven't had a chance to go through and fix the test cases yet. I'll get to it before RC2 next week. ------------------------------------------------------------------------ [2009-04-30 01:23:58] ivan dot rey at inpltda dot com I agree also. Full precision should be available for the developer. I wonder if recompiling php with a different CAP in In php-5.2.8\ext\standard\formatted_print.c I found this: #define MAX_FLOAT_PRECISION 40 is the actual solution or if it has some further implications. ------------------------------------------------------------------------ [2009-04-29 05:21:05] rasmus@php.net I agree with Rick here. The 40-digit limit is strangely arbitrary and doesn't match the size of the double. We are hiding available precision here. ------------------------------------------------------------------------ [2009-01-30 21:51:56] exploringbinary at gmail dot com Since I didn't find anything in the documentation, I poked around in the source code. In php-5.2.8\ext\standard\formatted_print.c I found this: #define MAX_FLOAT_PRECISION 40 There is no explanation as to why it's capped at 40. What's interesting is that this code prints only 40 decimal places (0.0000000000004547473508864641189575195312), without a warning: <?php /* Print 2^-41 */ $dyadic = 0.00000000000045474735088646411895751953125; printf ("%1.2147483646f",$dyadic); ?> While this code prints ``Warning: printf() [function.printf]: Precision must be greater than zero and less than 2147483647 ...'' <?php /* Print 2^-41 */ $dyadic = 0.00000000000045474735088646411895751953125; printf ("%1.2147483647f",$dyadic); ?> If you're going to warn about a maximum, why not warn about the real maximum -- 40, not 2147483646? I wrote an article about how this issue is handled in PHP and 7 other languages at http://www.exploringbinary.com/print-precision-of-dyadic-fractions-varies-by-language/ ------------------------------------------------------------------------ [2009-01-20 22:26:19] exploringbinary at gmail dot com Hi, I read the documentation and the "how to submit a bug report" and googled as well before (and now again after) submitting the bug report. I cannot see discussion of this limit. Could you please give me a more specific link? I would also like to know the rationale for the limit. Why doesn't javascript or gcc have this limit? Why did Microsoft accept my bug report for a similar problem in VS? It seems like something PHP should consider, or at least give rationale for why not. Thanks. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/47168 -- Edit this bug report at http://bugs.php.net/?id=47168&edit=1