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Re^4: The 10**21 Problem (Part 4)

by eyepopslikeamosquito (Chancellor)
on May 20, 2014 at 13:12 UTC ( #1086782=note: print w/replies, xml ) Need Help??


in reply to Re^3: The 10**21 Problem (Part 4)
in thread The 10**21 Problem (Part 4)

Yes, I believe you are correct.

From stringobject.c:

static long string_hash(PyStringObject *a) { register Py_ssize_t len; register unsigned char *p; register long x; if (a->ob_shash != -1) return a->ob_shash; len = Py_SIZE(a); p = (unsigned char *) a->ob_sval; x = *p << 7; while (--len >= 0) x = (1000003*x) ^ *p++; x ^= Py_SIZE(a); if (x == -1) x = -2; a->ob_shash = x; return x; }
we can see that it is not whether the platform itself is 64-bit that matters, but whether the long type used by the C compiler that Python was built with is 64-bit. For Python built with a 32-bit long my solution should work, for a 64-bit long it will not.

On 64-bit architectures, Windows C compilers tend to use the LLP64 programming model (32-bit long), while most others tend to use the LP64 model (64-bit long). From this stack overflow question:

The true "war" was for sizeof(long), where Microsoft decided for sizeof(long) == 4 (LLP64) while nearly everyone else decided for sizeof(long) == 8 (LP64). Note that a programming model is a choice made on a per-compiler basis, and several can coexist on the same OS. However, the programming model chosen as the primary model for the OS API typically dominates.

Hmmm, I see from this later stringobject.c that _Py_HashSecret_* has been added, presumably to protect against DoS attacks that exploit hash collisions in Python dictionaries.

static long string_hash(PyStringObject *a) { register Py_ssize_t len; register unsigned char *p; register long x; #ifdef Py_DEBUG assert(_Py_HashSecret_Initialized); #endif if (a->ob_shash != -1) return a->ob_shash; len = Py_SIZE(a); /* We make the hash of the empty string be 0, rather than using (prefix ^ suffix), since this slightly obfuscates the hash secre +t */ if (len == 0) { a->ob_shash = 0; return 0; } p = (unsigned char *) a->ob_sval; x = _Py_HashSecret.prefix; x ^= *p << 7; while (--len >= 0) x = (1000003*x) ^ *p++; x ^= Py_SIZE(a); x ^= _Py_HashSecret.suffix; if (x == -1) x = -2; a->ob_shash = x; return x; }

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[ambrus]: Corion: well Prima::Object says something like that the cleanup method will send an onDestory message and that you can't get more messages after cleanup, or something.
[Corion]: ambrus: Yeah - I don't think the deep source dive will be necessary if things are implemented as simple as they could be :)) And hopefully I won't need (more) timely object destruction. I can update the screen at 60Hz and hopefully even do HTTP ...
[Corion]: ... transfers in the background. Now that I think about it, this maybe even means that I can run the OpenGL filters on Youtube input :)
[ambrus]: Corion: I mentioned that the unix event loop of Prima always wakes up at least once every 0.2 seconds. Have you found out whether the win32 event loop of Prima does that too?
[Corion]: ambrus: Hmm - I would assume that the onDestroy message is sent from the destructor and doesn't go through the messageloop, but maybe it is sent when a window gets destroyed but all components are still alive...
[ambrus]: Corion: partly deep source dive, partly just conservative coding even if it adds an overhead.
[Corion]: ambrus: Hmm - no, I haven't looked at wakeup intervals ... I wonder why it should want to wakeup periodically because it gets a lot of messages from the Windows message loop (on Windows obviously)
[ambrus]: (Alternately a deep source dive and then rewrite that event loop to make it better, and then as a bonus you get an idle method.)
[ambrus]: The 0.2 seconds wakeup is likely a workaround for some bug, but I can't guess what bug that is.
[ambrus]: It's been there since Prima 1.00 iirc

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