decoding 代码贴一下。

最新推荐文章于 2025-07-05 22:26:11 发布

原创最新推荐文章于 2025-07-05 22:26:11 发布 · 367 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#exception #optimization #integer #byte #null #variables

本文介绍了一种基于有限域运算的碎片解码算法实现过程，该算法通过接收多个数据片段并利用特定参数进行解码，以恢复原始消息。文中详细展示了算法流程，包括初始化参数、计算相关方程以及最终解码步骤。

public static byte[] decode( byte[] rec_fragments, final int Nrec, final CosetIDAParameters p) //throws Exception { byte[] rec_message = new byte[p.getMessageLength()];//p.getMessageLength() int ExpFE; final int numSegments = p.getSegmentsPerSlice(); final int logOfField = p.getLogOfFieldLength(); final int[] COLBIT = InitField.getCOLBIT(logOfField); final int[] BIT = InitField.getBIT(logOfField); final int[] ExptoFE = InitField.getExptoFE(logOfField); final int[] FEtoExp = InitField.getFEtoExp(logOfField); final int numDataSlices = p.getNumDataSlices(); final int numCodeSlices = p.getNumCodeSlices(); Integer key = new Integer(p.getNumDataSlices() + numSegments * p.getNumCodeSlices() * logOfField); FiniteStack stack = (FiniteStack) _decodeTable.get(key); if (stack == null) { synchronized (_decodeTable) { if ((stack = (FiniteStack) _decodeTable.get(key)) == null) { Object bucket = null; stack = new FiniteStack(STACK_SIZE); if ((bucket = _decodeTable.put(key, stack)) != null) System.err.println("CosetDecode.decode: bucket=" + bucket + " for key=" + key + " stack=" + stack); } } } ArrayObj arrayObj = (ArrayObj) stack.pop(); if (arrayObj == null) arrayObj = new ArrayObj(p.getNumDataSlices(), p.getNumCodeSlices(), numSegments, logOfField); int[] Rec_index = arrayObj.Rec_index; int[] Col_Ind = arrayObj.Col_Ind; int[] Row_Ind = arrayObj.Row_Ind; byte[] M = arrayObj.M; int[] C = arrayObj.C; int[] D = arrayObj.D; int[] E = arrayObj.E; int[] F = arrayObj.F; if (Nrec < p.getNumDataSlices()+p.getNumCodeSlices()) { //throw new Exception("Decode error!!!!"); System.out.println("Decode error!!!!=========="+Nrec+"tot:"+(p.getNumDataSlices()+p.getNumCodeSlices())); } // coset ==================================================coset begin=============== // For Loop Iterators int itr, row, col, rowEquation, columnEquation; // Miscellaneous variables used in code slice calculation int sliceArrayPosition, messageArrayPosition; int ExpFEplusRow; int arrayPositionDifference, sliceArrayPositionPlusNumSegments; int sliceArrayIterator; final int[] equationBitMask = InitField.getBIT(p.getLogOfFieldLength()); final int[] exponentToFiniteFieldElement = InitField.getExptoFE(p.getLogOfFieldLength()); final int[] finiteFieldElementToExponent = InitField.getFEtoExp(p.getLogOfFieldLength()); final int multFieldSize = p.getMultiplicationFieldSize(); InitField.generateG(logOfField, numDataSlices, numCodeSlices); final int[][] G= InitField.getG(); for ( row = 0; row <numDataSlices; row++) { /** * Compute values of equations applied to message and fill into * fragment(row+DataSlices). */ final int rowOffset = ((row) * p.getSliceLength()); // p.getTotalSliceLength() /** * Second, fill in contents relevant portions of fragment */ for ( col = 0; col < numDataSlices+numCodeSlices ; col++) { //message->code messageArrayPosition = col * (p.getSliceLength()+1)+1; //if(messageArrayPosition==0)messageArrayPosition=1; // System.out.println("messageArrayPosition:"+messageArrayPosition); /* ExpFE = (multFieldSize - finiteFieldElementToExponent[row ^ col ^ COLBIT[0]]) % multFieldSize;*/ // System.out.println("row:"+row+"col:"+col); // System.out.println("G[row][col]:"+G[row][col]); ExpFE = finiteFieldElementToExponent[G[row][col]]; for (rowEquation = 0; rowEquation < logOfField; rowEquation++) { ExpFEplusRow = ExpFE + rowEquation; sliceArrayPosition = rowOffset + (rowEquation * numSegments); // System.out.println("rowOffset:"+rowOffset); // System.out.println("sliceArrayPosition:"+sliceArrayPosition); for (columnEquation = 0; columnEquation < logOfField; columnEquation++) { // System.out.print((exponentToFiniteFieldElement[ExpFE + columnEquation] & equationBitMask[rowEquation])>0?1:0); // System.out.println("columnEquation"+columnEquation+"ExpFEplusRow"); if ((exponentToFiniteFieldElement[ExpFE + columnEquation] & equationBitMask[rowEquation]) > 0) { /* * Warning: the following code is heavily optimized and difficult to read * The following loop is the result of much optimization * and is an attempt to use as few instructions as possible * within this very deeply nested loop. */ arrayPositionDifference = ((columnEquation * numSegments + messageArrayPosition) - sliceArrayPosition); sliceArrayPositionPlusNumSegments = sliceArrayPosition + numSegments; sliceArrayIterator = sliceArrayPosition; // System.out.println("numSegments"+numSegments+"sliceArrayPosition"+sliceArrayPosition+"sliceArrayPositionPlusNumSegments"+sliceArrayPositionPlusNumSegments+"sliceArrayIterator + arrayPositionDifference:"+(sliceArrayIterator + arrayPositionDifference)); assert(sliceArrayPosition<rec_message.length); while (sliceArrayIterator < sliceArrayPositionPlusNumSegments) { // System.out.println("sliceArrayIterator"+sliceArrayIterator+" arrayPositionDifference:"+( arrayPositionDifference)); //if(sliceArrayIterator==4144) sliceArrayIterator=4143; rec_message[sliceArrayIterator] ^= rec_fragments[sliceArrayIterator + arrayPositionDifference]; sliceArrayIterator++; } } } // System.out.print("/n"); } } } /* System.out.println("=======================rec_message=====================:"+rec_message.length); printHexString(rec_message); System.out.println("=======================rec_message=====================");*/ return rec_message; }