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´╗┐package  {
    import flash.utils.*;

    public class ADPCMDecoder {

        private var predictor:int;
        private var stepIndex:int;
        private var step:uint;

        public function ADPCMDecoder() {
        }

        public function init(p:int=0,si:int=0):void {
            predictor=p;
            stepIndex=si;
            step=stepTable[stepIndex];
        }

        public function decodeBlock(block:ByteArray,blockSamples:uint,outBuff:Vector.<Number>):void {

            var sample:Number;
            var i:uint=0;

            for(;i<blockSamples;) {

                var byte:uint=block.readByte();
                var nibble:uint;
                nibble=byte & 15;

                sample=parseNibble(nibble);
                outBuff[i++]=sample;

                nibble=(byte>>16) & 15;
                sample=parseNibble(nibble);
                outBuff[i++]=sample;

            }

        }

        private function parseNibble(nibble:uint):Number {
            stepIndex+=indexTable[nibble];
            if(stepIndex<0) {
                stepIndex=0;
            } else if(stepIndex>88) {
                stepIndex=88;
            }

            var diff:uint = step >> 3;
            if(nibble & 1) diff += step >> 2;
            if(nibble & 2) diff += step >> 1;
            if(nibble & 4) diff += step;

            if(nibble & 8) {
                predictor-=diff;
                if(predictor<-32767) {
                    predictor=-32767;
                }
            } else {
                predictor+=diff;
                if(predictor>32767) {
                    predictor=32767;
                }
            }

            //predictor+=(nibbleToNumber(nibble) + 0.5) * step / 4;

            step=stepTable[stepIndex];

            return predictor/32768.0;
        }

        private const stepTable:Array= [
            7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
            19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
            50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
            130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
            337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
            876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
            2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
            5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
            15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
        ];

        private const indexTable:Array= [
            -1, -1, -1, -1, 2, 4, 6, 8,
            -1, -1, -1, -1, 2, 4, 6, 8
        ];

        public static function nibbleToNumber(nibble:uint):Number {
            return [0,1,2,3,4,5,6,7,-8,-7,-6,-5,-4,-3,-2,-1][nibble];
        }

    }

}
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