CompareMem

[SMcNeill]

A little routine to quickly compare one mem block to another to see if they're identical or not.

Code: (Select All)

Declare CustomType Library

    Function memcmp% (ByVal s1%&, Byval s2%&, Byval n As _Offset)

End Declare



Randomize Timer



Screen _NewImage(1280, 720, 32)



'let's make this an unique and pretty image!

For i = 1 To 100

    Line (Rnd * _Width, Rnd * _Height)-(Rnd * width, Rnd * _Height), &HFF000000 + Rnd * &HFFFFFF, BF

Next



image1 = _CopyImage(0) 'identical copies for testing

image2 = _CopyImage(0) 'identical copy...  BUT

_Dest image2

PSet (Rnd * _Width, Rnd * _Height), &HFF000000 + Rnd * &HFFFFFF 'We've just tweaked it so that there's no way in hell it's the same as the other two now!

_Dest 0 'image3 is EXACTLY one pixel different from the other two.  Can we detect that?

image3 = _CopyImage(0) 'an identical copy once again, because 0 will change once we print the resul





Dim m(3) As _MEM

m(0) = _MemImage(0)

m(1) = _MemImage(image1)

m(2) = _MemImage(image2)

m(3) = _MemImage(image3)



result1 = CompareMem(m(0), m(1))

result2 = CompareMem(m(0), m(2))

result3 = CompareMem(m(1), m(2))



Print "Current Screen and Image 1 Compare:  "; result1

Print "Current Screen and Image 2 Compare:  "; result2

Print "Image1 and Image 2 Compare        :  "; result3



Print

Print "Press <ANY KEY> for a speed test!"

Sleep



t# = Timer

Limit = 1000

For i = 1 To Limit

    result = CompareMem(m(1), m(2))

    result = CompareMem(m(1), m(3))

Next

Print

Print Using "####.####### seconds to do"; Timer - t#;

Print Limit * 2; "comparisons of"; m(0).SIZE; "bytes."



Function CompareMem& (m1 As _MEM, m2 As _MEM)

    $Checking:Off

    If m1.SIZE <> m2.SIZE Then Exit Function 'not identical

    If m1.ELEMENTSIZE <> m2.ELEMENTSIZE Then Exit Function 'not identical

    If memcmp(m1.OFFSET, m2.OFFSET, m1.SIZE) = 0 Then x = -1 Else x = 0

    CompareMem = x

    $Checking:On

End Function

Demo here uses images and _MEMIMAGE to compare, as they're nice and quick to generate, duplicate, and alter.