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Rounding to the next power of two
Posted: Fri Jun 04, 2021 8:12 pm
by ❤x1
Code: Select all
Procedure RoundPow(Number)
Number - 1
Number = (Number | Number >> 1)
Number = (Number | Number >> 2)
Number = (Number | Number >> 4)
Number = (Number | Number >> 8)
Number = (Number | Number >> 16)
CompilerIf #PB_Compiler_Processor = #PB_Processor_x64
Number = (Number | Number >> 32)
CompilerEndIf
ProcedureReturn Number + 1
EndProcedure
Debug RoundPow(67)
Re: Rounding to the next power of two
Posted: Tue Jun 08, 2021 10:39 pm
by eck49
Clever!
A very elegant application of binary arithmetic.
Re: Rounding to the next power of two
Posted: Wed Jun 09, 2021 1:49 am
by BarryG
Since I'm a bit dumb, when would you need this type of trick? Can you give an example? I like to learn. Thanks.
Re: Rounding to the next power of two
Posted: Wed Jun 09, 2021 1:54 am
by Keya
I think you can also use the Intel assembly instruction "bsr" (bitscan reverse) for this
Re: Rounding to the next power of two
Posted: Wed Jun 09, 2021 1:58 am
by skywalk
This is faster than the direct way with pow() function. I will use it.
Useful when sampling discretely and FFT samples must be powers of 2.
Re: Rounding to the next power of two
Posted: Wed Jun 09, 2021 3:07 am
by idle
Yes a nice tip if you need to call it frequently the assembly equivalent would be like this.
Code: Select all
Procedure RoundPowUP(Number)
CompilerIf SizeOf(Integer) = 8
!mov rdx,[p.v_Number]
!sub rdx, 1
!bsr qword rcx , rdx
!add rcx,1
!shl rax,cl
CompilerElse
!mov edx,[p.v_Number]
!sub edx, 1
!bsr qword ecx , edx
!add ecx,1
!shl eax,cl
CompilerEndIf
ProcedureReturn
EndProcedure