107 lines
3.6 KiB
Java
107 lines
3.6 KiB
Java
package com.bytezone.diskbrowser.nib;
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// -----------------------------------------------------------------------------------//
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class DiskReader16Sector extends DiskReader
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// -----------------------------------------------------------------------------------//
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{
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private static final int RAW_BUFFER_SIZE = 342;
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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 byte[] encodeA = new byte[RAW_BUFFER_SIZE];
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private final byte[] encodeB = new byte[BUFFER_WITH_CHECKSUM_SIZE];
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private final ByteTranslator byteTranslator = new ByteTranslator6and2 ();
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// ---------------------------------------------------------------------------------//
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DiskReader16Sector ()
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// ---------------------------------------------------------------------------------//
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{
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super (16);
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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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// rearrange 342 bytes into 256
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byte[] decodedBuffer = new byte[SECTOR_SIZE]; // 256 bytes
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// convert legal disk values to actual 6 bit values
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for (int i = 0; i < BUFFER_WITH_CHECKSUM_SIZE; i++) // 343 bytes
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decodeA[i] = (byte) (byteTranslator.decode (buffer[offset++]) << 2);
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// reconstruct 342 bytes each with 6 bits
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byte chk = 0;
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for (int i = decodeB.length - 1; i >= 0; i--) // 342 bytes
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chk = decodeB[i] = (byte) (decodeA[i + 1] ^ chk);
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if ((chk ^ decodeA[0]) != 0)
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throw new DiskNibbleException ("Checksum failed");
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// move 6 bits into place
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for (int i = 0; i < SECTOR_SIZE; i++)
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decodedBuffer[i] = decodeB[i + 86];
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// reattach each byte's last 2 bits
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for (int i = 0, j = 86, k = 172; i < 86; i++, j++, k++)
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{
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byte val = decodeB[i];
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decodedBuffer[i] |= reverse ((val & 0x0C) >> 2);
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decodedBuffer[j] |= reverse ((val & 0x30) >> 4);
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if (k < SECTOR_SIZE)
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decodedBuffer[k] |= reverse ((val & 0xC0) >> 6);
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}
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return decodedBuffer;
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}
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// convert 256 data bytes into 342 translated bytes plus a checksum
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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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byte[] encodedBuffer = new byte[BUFFER_WITH_CHECKSUM_SIZE];
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// move data buffer down to make room for the 86 extra bytes
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for (int i = 0; i < SECTOR_SIZE; i++)
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encodeA[i + 86] = buffer[i];
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// build extra 86 bytes from the bits stripped from the data bytes
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for (int i = 0; i < 86; i++)
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{
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int b1 = reverse (buffer[i] & 0x03) << 2;
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int b2 = reverse (buffer[i + 86] & 0x03) << 4;
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if (i < 84)
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{
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int b3 = reverse (buffer[i + 172] & 0x03) << 6;
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encodeA[i] = (byte) (b1 | b2 | b3);
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}
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else
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encodeA[i] = (byte) (b1 | b2);
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}
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// convert into checksum bytes
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byte checksum = 0;
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for (int i = 0; i < RAW_BUFFER_SIZE; i++)
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{
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encodeB[i] = (byte) (checksum ^ encodeA[i]);
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checksum = encodeA[i];
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}
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encodeB[RAW_BUFFER_SIZE] = checksum; // add checksum to the end
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// remove two bits and convert to translated bytes
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for (int i = 0; i < BUFFER_WITH_CHECKSUM_SIZE; i++)
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encodedBuffer[i] = byteTranslator.encode (encodeB[i]);
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return encodedBuffer;
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}
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}
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