[bb] Multi-Dimensional Arrays using a Single Array by Techlord [ 1+ years ago ]

[BlitzBot]

Title : Multi-Dimensional Arrays using a Single Array
Author : Techlord
Posted : 1+ years ago

Description : This code snippet, illustrates the formula that will compute the offset into memory for an array with any number of dimensions:

Code Select Expand

Graphics 1024,768
n=Input("Number of Array Dimensions: ")
ascii= 96
element$=Chr(ascii+loop+1)
dimensions$="a"
For loop = 1 To n
Print "Dim Array("+dimensions+")"
Print "linear_index=base_index+"+String("(",loop)+"a_index)" + expressions$ + "*element_size_in_bytes"
Print
element$=Chr(ascii+loop+1)
expression$="*"+element$+"_size+"+element$+"_index)"
expressions$=expressions$+expression$
dimensions$=dimensions$+","+element$
NextThere is no magic addressing mode that lets you easily access elements of multidimensional arrays. They require some work and lots of instructions even at the compiler level. This formula is employed by most high level programming languages including Pascal, C/C++, Java, Ada, Modula-2, etc.

Below is an example of how to apply the formula. Hope someone finds this useful. [/i]

Code :

Code (blitzbasic) Select Expand

;bscvmArray an excerpt from the BlitzScript3D Engine
; @ http://www.blitzbasic.com/Community/posts.php?topic=39622
;Supports up to 4 dimensions using Row Major Ordering Formula
; @ webster.cs.ucr.edu/AoA/Windows/HTML/Arraysa2.html
;There is a generic formula that will compute the offset into memory For an array
;with any number of dimensions, however, you'll rarely use more than four.

Global blitzscriptVar[65535] ;a single dimension array

Type bscvmArray
Field name$
Field i_size
Field j_size
Field k_size
Field l_size
Field head
Field tail
End Type

Function bscvmArrayCreate.bscvmArray(i,j=0,k=0,l=0)
this.bscvmArray = New bscvmArray
thisi_size=i+1
thisj_size=j+1
thisk_size=k+1
thisl_size=l+1
thishead=0
this ail=thishead + thisi_size * thisj_size * thisk_size * thisl_size
Return this
End Function

Function bscvmArrayGet(this.bscvmArray,i_index,j_index=0,k_index=0,l_index=0)
Return blitzscriptVar[thishead+(((i_index * thisj_size+j_index) * thisk_size+k_index) * thisl_size+l_index)]
End Function

Function bscvmArraySet(this.bscvmArray,i_index,j_index=0,k_index=0,l_index=0,value$=0)
blitzscriptVar[thishead+(((i_index * thisj_size+j_index) * thisk_size+k_index) * thisl_size+l_index)]=value
End Function

Function bscvmArrayLinearIndexGet(this.bscvmArray,i_index,j_index=0,k_index=0,l_index=0)
Return thishead+(((i_index * thisj_size+j_index) * thisk_size+k_index) * thisl_size+l_index)
End Function

Function bscvmArrayTest()

this.bscvmArray=bscvmArrayCreate(3,3,3,3)

For i =  0 To 3
For j =  0 To 3
For k =  0 To 3
For l =  0 To 3

DebugLog(i+","+j+","+k+","+l+"= "+m+" /  "+bscvmArrayLinearIndexGet(this,i,j,k,l))
m=m+1

Next
Next
Next
Next
DebugLog "tail="+this ail

End Function

bscvmArrayTest()

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