86 lines
3.0 KiB
Java
86 lines
3.0 KiB
Java
package com.bytezone.diskbrowser.nib;
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// -----------------------------------------------------------------------------------//
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class DiskReader13Sector extends DiskReader
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// -----------------------------------------------------------------------------------//
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{
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private static final int RAW_BUFFER_SIZE = 410;
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private static final int BUFFER_WITH_CHECKSUM_SIZE = RAW_BUFFER_SIZE + 1;
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private final byte[] decodeA = new byte[BUFFER_WITH_CHECKSUM_SIZE];
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private final byte[] decodeB = new byte[RAW_BUFFER_SIZE];
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private final ByteTranslator byteTranslator = new ByteTranslator5and3 ();
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// ---------------------------------------------------------------------------------//
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DiskReader13Sector ()
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// ---------------------------------------------------------------------------------//
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{
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super (13);
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}
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// ---------------------------------------------------------------------------------//
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@Override
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byte[] decodeSector (byte[] buffer, int offset) throws DiskNibbleException
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// ---------------------------------------------------------------------------------//
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{
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byte[] decodedBuffer = new byte[SECTOR_SIZE];
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// convert legal disk values to actual 5 bit values
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for (int i = 0; i < BUFFER_WITH_CHECKSUM_SIZE; i++) // 411 bytes
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decodeA[i] = (byte) (byteTranslator.decode (buffer[offset++]) << 3);
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// reconstruct 410 bytes each with 5 bits
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byte chk = 0;
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int ptr = 0;
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for (int i = 409; i >= 256; i--) // 154 bytes
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chk = decodeB[i] = (byte) (decodeA[ptr++] ^ chk);
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for (int i = 0; i < 256; i++) // 256 bytes
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chk = decodeB[i] = (byte) (decodeA[ptr++] ^ chk);
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if ((chk ^ decodeA[ptr]) != 0)
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throw new DiskNibbleException ("Checksum failed");
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// rearrange 410 bytes into 256
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byte[] k = new byte[8];
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final int[] lines = { 0, 51, 102, 153, 204, 256, 307, 358 }; // 255 is skipped
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// process 8 disk bytes at a time, giving 5 valid bytes
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// do this 51 times, giving 255 bytes
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ptr = 0;
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for (int i = 50; i >= 0; i--)
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{
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for (int j = 0; j < 8; j++)
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k[j] = decodeB[i + lines[j]];
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k[0] |= (k[5] & 0xE0) >>> 5;
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k[1] |= (k[6] & 0xE0) >>> 5;
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k[2] |= (k[7] & 0xE0) >>> 5;
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k[3] |= (k[5] & 0x10) >>> 2;
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k[3] |= (k[6] & 0x10) >>> 3;
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k[3] |= (k[7] & 0x10) >>> 4;
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k[4] |= (k[5] & 0x08) >>> 1;
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k[4] |= (k[6] & 0x08) >>> 2;
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k[4] |= (k[7] & 0x08) >>> 3;
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for (int j = 0; j < 5; j++)
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decodedBuffer[ptr++] = k[j];
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}
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// add last byte
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decodedBuffer[ptr] = (byte) (decodeB[255] | ((decodeB[409] & 0x3F) >>> 3));
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return decodedBuffer;
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}
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// ---------------------------------------------------------------------------------//
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@Override
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byte[] encodeSector (byte[] buffer)
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// ---------------------------------------------------------------------------------//
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{
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System.out.println ("encodeSector() not written");
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return null;
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}
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}
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