Code archives/Algorithms/Single Byte Arrays

;Single, Double Byte Arrays
;PJ 2015

Type Array
	Field Bank
	Field Width
	Field X
	Field Y
End Type

Function DefineArray(Width=1,x=1,y=1)
	y=Abs(y)
	x=Abs(x)
	
	If (Not (x Or y))
		RuntimeError "Array must have dimensions"
	End If
	
	Local NewArray.Array=New Array
	NewArray\Width=Width
	NewArray\X=x
	NewArray\Y=y
	NewArray\Bank=CreateBank(x*y*Width)
	Return Handle(NewArray)
End Function

Function SetArrayElement(Array, Value, x=1, y=1)
	Local Instance.Array=Object.Array(Array)
	Local Offset=(((y-1) * (Instance\X*Instance\Width))+(x*Instance\Width))-1
	
	Select (Instance\Width)
		Case 1:
			PokeByte Instance\Bank,Offset,Value And 255
		Case 2:
			PokeShort Instance\Bank,Offset,Value And 65535
	;	Case 3:
	;		PokeByte Instance\Bank,Offset,(Value Shr 24) And 255
	;		PokeShort Instance\Bank,Offset+1,Value And 65535
		Case 4:
			PokeInt Instance\Bank,Offset,Value
		Default:
			;Invalid Width
	End Select
End Function

Function GetArrayElement(Array,x=1,y=1)
	Local Instance.Array=Object.Array(Array)
	Local Offset=(((y-1) * (Instance\X*Instance\Width))+(x*Instance\Width))-1
	
	Local Element
	Select (Instance\Width)
		Case 1:
			Element=PeekByte(Instance\Bank,Offset) And 255
		Case 2:
			Element=PeekShort(Instance\Bank,Offset) And 65535
	;	Case 3:
	;		Element=PeekByte(Instance\Bank,Offset) Shl 24
	;		Element=Element+(PeekShort(Instance\Bank,Offset+1) And 65535)
		Case 4:
			Element=PeekInt(Instance\Bank,Offset)
		Default:
			;Invalid Width
	End Select
	
	Return Element
End Function

Function ResizeArray(Array,x,y=1)
	Local Instance.Array=Object.Array(Array)
	
	Local OldSize=BankSize(Instance\Bank)
	Local NewSize=(x*y*Instance\Width)
	
	If (NewSize=OldSize)
		Return
	End If
	
	If (NewSize<OldSize)
		Local Byte
		For Byte=NewSize To OldSize-1
			PokeByte Instance\Bank,Byte,0
		Next
		OldSize=NewSize
	End If
	
	Local NewBank=CreateBank(NewSize)
	CopyBank Instance\Bank,0,NewBank,0,OldSize-1
	
	FreeBank Instance\Bank
	
	Instance\Bank=NewBank
	
	Instance\X=x
	Instance\Y=y
	
End Function

Function FreeArray(Array)
	Local Instance.Array=Object.Array(Array)
	FreeBank Instance\Bank
	Instance\X=0
	Instance\Y=0
	Instance\Width=0
	Delete Instance
End Function

 ;; Coded by VirtLands,  { Jan 06, 2015 }

 Graphics 500,640,32,2
 Print
 Print

 Global ByteMask[4]

 ByteMask[0] = $FFFFFF00
 ByteMask[1] = $FFFF00FF
 ByteMask[2] = $FF00FFFF
 ByteMask[3] = $00FFFFFF

 ;;  Use an  INT array, and access it at BYTE offsets ... ( As if we were accessing a BYTE array )

 Dim C(4194304)   ;;   Create an array with enough room for 16777216 bytes.

 ;;____  ( 4194304 * 4 = 16777216 )

 ;;____  Do some testing to prove that the functions work.

 For z = 0 To 20
           StoreByte_at_index( z*2, z )       ;; Take the first 21 numbers and multiply x 2.            
 Next 

 For z = 0 To 20       
           Print " z = "+z+" : "+ GetByte_at_index( z )  ;;; .. Read back the results ..
 Next 

 Print 

 For z = 0 To 20
           StoreByte_at_index( z+100, z )     ;; Take the first 21 numbers and add +100.
 Next 

 For z = 0 To 20          
           Print " z = "+z+" : "+ GetByte_at_index( z )  ;;; .. Read back the results ..
 Next 

 WaitKey():End 


;; ... Stores a byte value at a byte index,  ( starting at offset zero, and using Little-Endian storage methods ) 
Function StoreByte_at_index( byte, index )

        div  = index Shr 2    ;; divide it by 4
        rem = index Mod 4  ;; find the remainder

        v = C(div)                 ;; read the current INT C(..) value

        v = v And ByteMask[rem]       ;; Clear the target byte to zero.

        v = v Or byte Shl (rem Shl 3)  ;; Update that byte to a new value.  

        C(div) = v   ;; upate that INT memory.

End Function 

;; ... Retrieves a byte value, using a byte offset index,  (starting at offset zero). 
Function GetByte_at_index%( index )

      div = index Shr 2
      rem = index Mod 4

      v = C(div)     
      v = (v Shr (rem Shl 3)) And $FF   ;; .... 0_0 

      Return v

End Function