Print Page - Unique seed generator for random algorithms.

Title: Unique seed generator for random algorithms.
Post by: hutch-- on August 20, 2021, 10:30:52 AM

Not every random number generator is a stellar performer and some are downright awful but there is a simple trick to get better results, simply by re-seeding the random number generator below the range where the random numbers repeat. The code is simple and easy enough to understand but you need to understand that as it is run asynchronously in its own thread, there will be a minor time lag between resuming the thread and getting the result in the GLOBAL variable rseed.

In the example below, a "waitkey$" provides that slight pause so that the thread runs to completion. It is designed to be used with a random number generator that runs long enough for the thread to run to completion and for the next re-seeding, a new seed is available without pausing the random generator.

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#compile exe "rseed.exe"

#include "\basic\include\win32api.inc"

GLOBAL hThread as DWORD
GLOBAL tID as DWORD
GLOBAL rseed as DWORD
GLOBAL sd1 as DWORD
GLOBAL sd2 as DWORD

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FUNCTION PBmain as LONG

hThread = CreateThread(ByVal 0,0,ByVal CodePtr(ReturnSeed),0,%CREATE_SUSPENDED,ByVal tID)

ResumeThread hThread

StdOut "Press any key to view result ...."+$CRLF
waitkey$
' ----------------------------------
StdOut left$(hex$(sd1),4)+" hex 1st 2 bytes"
StdOut left$(hex$(sd2),4)+" hex 2nd 2 bytes"+$CRLF
StdOut hex$(rseed,8)+" hex combined 4 bytes"+$CRLF
' ----------------------------------
StdOut "Press any key to exit ...."+$CRLF
waitkey$

End FUNCTION

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FUNCTION ReturnSeed(ByVal unused as DWORD) as DWORD

lbl:
! cpuid
! rdtsc
! bswap eax
! mov sd1, eax

! cpuid
! rdtsc
! bswap eax
! mov sd2, eax

! mov ecx, sd1
! mov eax, sd2
! ror ecx, 16
! mov ax, cx

! mov rseed, eax

SuspendThread GetCurrentThread
! jmp lbl

End FUNCTION

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Title: Re: Unique seed generator for random algorithms.
Post by: Adamanteus on August 20, 2021, 11:22:41 PM

Not clear for what is here cpuid ?!

Title: Re: Unique seed generator for random algorithms.
Post by: hutch-- on August 21, 2021, 12:45:04 AM

Serialise instruction, forces all instructions to complete. Produces a slight delay and clears the instruction cache.

Title: Re: Unique seed generator for random algorithms.
Post by: Adamanteus on August 21, 2021, 03:25:04 AM

Yes, unique - but in thread, could be called srand for simplify :eusa_boohoo:

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Specialised Projects => PowerBASIC => Topic started by: hutch-- on August 20, 2021, 10:30:52 AM