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    <p>Your asm code is relativity slow because use stack end write 8 times to memory. Check this one...</p> <pre><code>procedure DecodePixels(EncPixels: Byte; var DecPixels: TDecodedPixels); asm xor ecx, ecx add al, al rcl ecx, 8 add al, al rcl ecx, 8 add al, al rcl ecx, 8 add al, al rcl ecx, 1 mov [DecPixels + 4], ecx xor ecx, ecx add al, al rcl ecx, 8 add al, al rcl ecx, 8 add al, al rcl ecx, 8 add al, al rcl ecx, 1 mov [DecPixels], ecx end; </code></pre> <p>Maybe is even faster than code with lookup table!</p> <p>Improved version:</p> <pre><code>procedure DecodePixelsI(EncPixels: Byte; var DecPixels: TDecodedPixels); asm mov ecx, 0 //Faster than: xor ecx, ecx add al, al rcl ch, 1 add al, al rcl cl, 1 ror ecx, 16 add al, al rcl ch, 1 add al, al rcl cl, 1 mov [DecPixels + 4], ecx mov ecx, 0 //Faster than: xor ecx, ecx add al, al rcl ch, 1 add al, al rcl cl, 1 ror ecx, 16 add al, al rcl ch, 1 add al, al rcl cl, 1 mov [DecPixels], ecx end; </code></pre> <p>Version 3:</p> <pre><code>procedure DecodePixelsX(EncPixels: Byte; var DecPixels: TDecodedPixels); asm add al, al setc byte ptr[DecPixels + 7] add al, al setc byte ptr[DecPixels + 6] add al, al setc byte ptr[DecPixels + 5] add al, al setc byte ptr[DecPixels + 4] add al, al setc byte ptr[DecPixels + 3] add al, al setc byte ptr[DecPixels + 2] add al, al setc byte ptr[DecPixels + 1] setnz byte ptr[DecPixels] end; </code></pre> <p>Version 4:</p> <pre><code>const Uint32DecPix : array [0..15] of cardinal = ( $00000000, $00000001, $00000100, $00000101, $00010000, $00010001, $00010100, $00010101, $01000000, $01000001, $01000100, $01000101, $01010000, $01010001, $01010100, $01010101 ); procedure DecodePixelsY(EncPixels: byte; var DecPixels: TDecodedPixels); inline; begin pcardinal(@DecPixels)^ := Uint32DecPix[EncPixels and $0F]; pcardinal(cardinal(@DecPixels) + 4)^ := Uint32DecPix[(EncPixels and $F0) shr 4]; end; </code></pre>
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    1. COThanks GJ for your interests. Unfortunately your routine is the slowests from every routines in my tests. See updated results in my answer. Once again thanks, will analyze your routine later.
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    2. COJeah... I didn't test it... I have forgotn that instruction "rcl ecx, 8" is slow. So the new version is about 3 times faster.
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    3. COHow did you measure that it is 3 times faster? It is about 40% faster according to my tests. +1 For the new method.
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