Re: [PHP] Bitwise AND for 31-st bit
On Tuesday 17 May 2011 22:06:34 David Harkness wrote: It appears that PHP is truncating the constant 0x8000 to be within MIN_INT and MAX_INT instead of as a bit field, but when shifting 1 31 it doesn't do apply any constraints. That's pretty typical of bit-manipulation: it will merrily slide 1 bits off either end. This explains why produces 0 as it's doing 0x8000 0x7FFF. It also explains the second tests. Yes, that's it! I slightly expanded test output and now it's clear that you are right: $tst1 = (1 31); $tst2 = 0x8000; $tst1_eq = $tst1 0x8000; $tst2_eq = $tst2 0x8000; $str1 = sprintf(%1$032b, $tst1); $str2 = sprintf(%1$032b, $tst2); print tst1=$tst1 ($str1), tst1_eq=$tst1_eq, tst1_type=.gettype($tst1).\n; print tst2=$tst2 ($str2), tst2_eq=$tst2_eq, tst2_type=.gettype($tst2).\n; produces this output: tst1=-2147483648 (1000), tst1_eq=0, tst1_type=integer tst2=2147483647 (0111), tst2_eq=2147483647, tst2_type=integer Now it is obvious to me that PHP 5.2 clamps explicit constants to MAX_INT. Weird, b... On 64-bit 5.3.3 I get tst1=2147483648, tst1_eq=2147483648, tst1_type=integer tst2=2147483648, tst2_eq=2147483648, tst2_type=integer If I try the 64-bit-equivalent code I get tst1=-9223372036854775808, tst1_eq=-9223372036854775808, tst1_type=integer tst2=9.22337203685E+18, tst2_eq=-9223372036854775808, tst2_type=double I get similar results with 5.3 on my amd64 host too. It works as it should, no weirdness. Glad to know that 5.3 get it fixed. Pity to me that I can not update my 5.2 on ARM board. -- Vitalii Demianets -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
[PHP] Bitwise AND for 31-st bit
Hello, all! I've encountered odd behavior of PHP regarding bitwise AND operation when dealing with 31-st bit, and kindly ask to give me some pointers. Consider the following snippet: $tst1 = (1 31); $tst2 = 0x8000; $tst1_eq = $tst1 0x8000; $tst2_eq = $tst2 0x8000; print tst1=$tst1, tst1_eq=$tst1_eq, tst1_type=.gettype($tst1).\n; print tst2=$tst2, tst2_eq=$tst2_eq, tst2_type=.gettype($tst2).\n; The output is: tst1=-2147483648, tst1_eq=0, tst1_type=integer tst2=2147483647, tst2_eq=2147483647, tst2_type=integer And I totally can not understand, why in the hell tst1_eq=0 ? (BTW I'm using PHP 5.2.14 on 32-bit CPU, if that matters) Sorry if this is well-known feature and have discussed before. In such a case please point me to the URL of the discussion. -- Vitalii Demianets -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Bitwise AND for 31-st bit
Hi, Hmm.. interesting... tst1=-2147483648, tst1_eq=-2147483648, tst1_type=integer tst2=2147483648, tst2_eq=-2147483648, tst2_type=double at me... PHP Version 5.3.3-1ubuntu9.5 (Apache 2.0 - i686) Valentine On Tue, May 17, 2011 at 5:19 PM, Vitalii Demianets vi...@nppfactor.kiev.uawrote: Hello, all! I've encountered odd behavior of PHP regarding bitwise AND operation when dealing with 31-st bit, and kindly ask to give me some pointers. Consider the following snippet: $tst1 = (1 31); $tst2 = 0x8000; $tst1_eq = $tst1 0x8000; $tst2_eq = $tst2 0x8000; print tst1=$tst1, tst1_eq=$tst1_eq, tst1_type=.gettype($tst1).\n; print tst2=$tst2, tst2_eq=$tst2_eq, tst2_type=.gettype($tst2).\n; The output is: tst1=-2147483648, tst1_eq=0, tst1_type=integer tst2=2147483647, tst2_eq=2147483647, tst2_type=integer And I totally can not understand, why in the hell tst1_eq=0 ? (BTW I'm using PHP 5.2.14 on 32-bit CPU, if that matters) Sorry if this is well-known feature and have discussed before. In such a case please point me to the URL of the discussion. -- Vitalii Demianets -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Bitwise AND for 31-st bit
On Tuesday 17 May 2011 18:31:00 Bálint Horváth wrote: Hi, Hmm.. interesting... tst1=-2147483648, tst1_eq=-2147483648, tst1_type=integer tst2=2147483648, tst2_eq=-2147483648, tst2_type=double at me... PHP Version 5.3.3-1ubuntu9.5 (Apache 2.0 - i686) That is what I expected too. There are 2 possibilities: 1) There was a bug in 5.2.14 which is fixed in 5.3.3; 2) There still is a bug in latest version of PHP which manifest itself only on ARM CPU (which I am working on). The worst thing is that I can not compile PHP 5.3.x for my board at the moment. So, I think, I should live with it, until I manage somehow to upgrade PHP installation for that board. -- Vitalii Demianets -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Bitwise AND for 31-st bit
It appears that PHP is truncating the constant 0x8000 to be within MIN_INT and MAX_INT instead of as a bit field, but when shifting 1 31 it doesn't do apply any constraints. That's pretty typical of bit-manipulation: it will merrily slide 1 bits off either end. This explains why produces 0 as it's doing 0x8000 0x7FFF. It also explains the second tests. On 64-bit 5.3.3 I get tst1=2147483648, tst1_eq=2147483648, tst1_type=integer tst2=2147483648, tst2_eq=2147483648, tst2_type=integer If I try the 64-bit-equivalent code I get tst1=-9223372036854775808, tst1_eq=-9223372036854775808, tst1_type=integer tst2=9.22337203685E+18, tst2_eq=-9223372036854775808, tst2_type=double David
