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Old 2008-10-13, 02:49   #1
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Default 64bit prime 95

Does using the 64bit binary of Prime95 significantly change the speed of the program?
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Old 2008-10-13, 03:04   #2
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No
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Old 2008-10-13, 03:19   #3
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Quote:
Originally Posted by Prime95 View Post
No


.... Then, why is it provided? Does it not help in trial factoring?
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Old 2008-10-14, 04:52   #4
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The 64 bit version of Prime95 used with the 64 bit version of Windows XP does trial factoring twice as fast as the 32 bit versions of the same software.
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Old 2008-10-14, 15:04   #5
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Quote:
Originally Posted by RMAC9.5 View Post
The 64 bit version of Prime95 used with the 64 bit version of Windows XP does trial factoring twice as fast as the 32 bit versions of the same software.

So, the linux 64 bit version doesnt work? Could you be very explicit in the differences between versions?
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Old 2008-10-15, 18:18   #6
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I don't have any experience with Linux (either the 32 bit or 64 bit distributions).
Consequently, I can't help you there. For the windows environment I can provide some additional information and some history which might be helpful to you.
When AMD extended the X86 ISA from 32 bits to 64 bits, they added 8 general purpose registers to their X86 hardware. However, these GP registers are only available for 64 bit CPUs running 64 bit operating systems. George was able to make use of these extra registers for trial factoring when he created the 64 bit version of Prime95. Consequently, Prime95 (64 bit) factoring on Windows XP (64 bit) is about twice as fast as Prime95 (32 bit) factoring on Windows XP (64 bit) or Windows XP (32 bit). Unfortunately, George, wasn't able to speed up his Prime95 (64 bit) LL code like he did for his trial factoring code.

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Old 2008-10-15, 23:20   #7
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It's frustrating that doubling the speed of trial factoring means
that it becomes profitable for only one more power of 2.

Last fiddled with by davieddy on 2008-10-15 at 23:38
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Old 2008-10-16, 00:33   #8
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Quote:
Originally Posted by davieddy View Post
It's frustrating that doubling the speed of trial factoring means that it becomes profitable for only one more power of 2.
Look at the bright side: TF to one more bit level means that P-1 after unsuccessful TF has a lower probability of finding a factor, for a given set of B1/B2 limits, so Prime95 will calculate that it is less worthwhile to do the P-1, so it will use lower B1/B2 limits than it would have if the TF had been done to only a lower power-of-2. _There's_ your speedup!
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