PureBasic Forum :: View topic - Configurable CRC procedure (1

Procedure.l CRC(*Buffer, Size)

Static.l Width = 32
Static.l Poly = $04c11db7
Static.l Init = -1
Static.l RefIn = #True
Static.l RefOut = #True
Static.l XOrOut = -1

Static.l M
Static Dim T.l(1023)
Protected.l i,j,C,R,*B1.Ascii,*B4.Long

; Calculate CRC lookup table
If Not M
M=~((-2)<<(Width-1))
If RefIn
R=0: For i=1 To Width: R|((Poly>>(i-1))&1)<<(Width-i): Next
Else
R=Poly<<(32-Width)
EndIf
For i=0 To 255
If RefIn
C=i: For j=0 To 7: C=((C>>1)&$7fffffff)!((-(C&1))&R): Next
Else
C=i<<24: For j=0 To 7: C=(C<<1)!((C>>31)&R): Next
C=(C<<24)|(((C>>8)&255)<<16)|(((C>>16)&255)<<8)|((C>>24)&255)
EndIf
T(i)=C
Next
For i=0 To 255
C=T(i): For j=1 To 3: C=((C>>8)&$ffffff)!T(C&255): T((j<<8)|i)=C: Next
Next
EndIf

; 4 byte loop
C=Init&M: *B4=*Buffer
While Size >= 4
C!*B4\l: *B4+4: Size-4
C=T(C&255+768)!T(((C>>8)&255)+512)!T(((C>>16)&255)+256)!T(((C>>24)&255))
Wend

; 1 byte loop
*B1=*B4
While Size
C=((C>>8)&$ffffff)!T((C!*B1\a)&255)
*B1+1: Size-1
Wend

; Finalize and output CRC
If Not RefIn
C=((C<<24)|(((C>>8)&255)<<16)|(((C>>16)&255)<<8)|((C>>24)&255))>>(32-Width)
EndIf
If RefOut<>RefIn
R=0: For i=1 To Width: R|((C>>(i-1))&1)<<(Width-i): Next: C=R
EndIf
ProcedureReturn (C!XOrOut)&M

EndProcedure

Author:	wilbert [ Sat Aug 24, 2019 3:34 pm ]
Post subject:	Configurable CRC procedure (1 - 32 bits)
After workin on a CRC module ( viewtopic.php?f=12&t=73462 ), I realized that I could do most of it in a single procedure without the use of asm. It's not as fast and doesn't support CRC with a width above 32 bits but seems to work fine. In it's current configuration, the result is the same as the PB builtin CRC32 algorithm. Some other often used configurations ... CRC-16/CCITT: Width=16, Poly=$1021, Init=$ffff, RefIn=#False, RefOut=#False, XOrOut=0 CRC-16/MODBUS: Width=16, Poly=$8005, Init=$ffff, RefIn=#True, RefOut=#True, XOrOut=0 For more of them, see http://reveng.sourceforge.net/crc-catalogue/ Code: Procedure.l CRC(Buffer, Size) Static.l Width = 32 Static.l Poly = $04c11db7 Static.l Init = -1 Static.l RefIn = #True Static.l RefOut = #True Static.l XOrOut = -1 Static.l M Static Dim T.l(1023) Protected.l i,j,C,R,B1.Ascii,B4.Long ; Calculate CRC lookup table If Not M M=~((-2)<<(Width-1)) If RefIn R=0: For i=1 To Width: R\|((Poly>>(i-1))&1)<<(Width-i): Next Else R=Poly<<(32-Width) EndIf For i=0 To 255 If RefIn C=i: For j=0 To 7: C=((C>>1)&$7fffffff)!((-(C&1))&R): Next Else C=i<<24: For j=0 To 7: C=(C<<1)!((C>>31)&R): Next C=(C<<24)\|(((C>>8)&255)<<16)\|(((C>>16)&255)<<8)\|((C>>24)&255) EndIf T(i)=C Next For i=0 To 255 C=T(i): For j=1 To 3: C=((C>>8)&$ffffff)!T(C&255): T((j<<8)\|i)=C: Next Next EndIf ; 4 byte loop C=Init&M: B4=Buffer While Size >= 4 C!B4\l: B4+4: Size-4 C=T(C&255+768)!T(((C>>8)&255)+512)!T(((C>>16)&255)+256)!T(((C>>24)&255)) Wend ; 1 byte loop B1=B4 While Size C=((C>>8)&$ffffff)!T((C!B1\a)&255) *B1+1: Size-1 Wend ; Finalize and output CRC If Not RefIn C=((C<<24)\|(((C>>8)&255)<<16)\|(((C>>16)&255)<<8)\|((C>>24)&255))>>(32-Width) EndIf If RefOut<>RefIn R=0: For i=1 To Width: R\|((C>>(i-1))&1)<<(Width-i): Next: C=R EndIf ProcedureReturn (C!XOrOut)&M EndProcedure

Author:	Kwai chang caine [ Sat Aug 24, 2019 7:16 pm ]
Post subject:	Re: Configurable CRC procedure (1 - 32 bits)
That works to on the same machine I obtain "378246432" all the time Code: Mem = AllocateMemory(1234567, #PB_Memory_NoClear) RandomSeed(0) RandomData(Mem, 1234567) Debug CRC(Mem, 1234567) FreeMemory(Mem)

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