Read JPG size in Neko

gistfile1.hx

var b = bytes.get;
var s = bytes.readString;
var i = 0;
var l = bytes.length;

if (b(i) == 0xFF && b(i+1) == 0xD8 && b(i+2) == 0xFF && b(i+3) == 0xE0)
{
	i += 4;

	if (s(i+2,1) == "J" && s(i+3,1) == "F" && s(i+4,1) == "I" && s(i+5,1) == "F" && b(i+6) == 0x00)
	{
		var block = b(i) * 256 + b(i+1);

		while (i < l)
		{
			// Increase the file index to get to the next block
			i += block;

			// Check for end of file
			if (i > l) throw "EOF";

			// Check that we are truly at the start of another block
			if (b(i) != 0xFF) throw "Not really a block!";
			
			// 0xFFC0 is the "Start of frame" marker which contains the file size
			if (b(i+1) == 0xC0)
			{            
				//The structure of the 0xFFC0 block is quite simple [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
				var height = b(i+5) * 256 + b(i+6);
				var width = b(i+7) * 256 + b(i+8);
				
				return {width:width, height:height};
			}
			else
			{
				// skip to next block marker
				i += 2;

				//Go to the next block
				block = b(i) * 256 + b(i+1);
			}
		}
	}
}