Apple-2-Tools/dmolony-DiskBrowser
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tidying

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This commit is contained in:
Denis Molony 2019-09-05 12:02:34 +10:00
parent 4ebfb65f24
commit c840ddf223
1 changed files with 22 additions and 21 deletions
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43
src/com/bytezone/diskbrowser/nib/DiskReaderGCR.java
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@ -15,24 +15,25 @@ public class DiskReaderGCR extends DiskReader
// ---------------------------------------------------------------------------------// // ---------------------------------------------------------------------------------//
@Override @Override
byte[] decodeSector (byte[] buffer, int ptr) throws DiskNibbleException byte[] decodeSector (byte[] inBuffer, int inPtr) throws DiskNibbleException
// ---------------------------------------------------------------------------------// // ---------------------------------------------------------------------------------//
{ {
byte[] outBuffer = new byte[BLOCK_SIZE * 2 + 12]; // 524 bytes byte[] outBuffer = new byte[BLOCK_SIZE * 2 + 12]; // 524 bytes
int outPtr = 0; int outPtr = 0;
int[] checksums = new int[3]; int[] checksums = new int[3];
// decode four disk bytes into three data bytes (175 * 3 - 1 = 524) // decode four disk bytes into three data bytes (175 * 3 - 1 = 524)
for (int j = 0; j < 175; j++) for (int j = 0; j < 175; j++)
{ {
checksums[0] = (checksums[0] & 0xFF) << 1; // ROL // ROL first checksum
if ((checksums[0] > 0xFF)) checksums[0] = (checksums[0] & 0xFF) << 1; // shift left
++checksums[0]; if ((checksums[0] > 0xFF)) // check for overflow
++checksums[0]; // update bit 0
// 6&2 translation // 6&2 translation
byte d3 = byteTranslator.decode (buffer[ptr++]); // composite byte byte d3 = byteTranslator.decode (inBuffer[inPtr++]); // composite byte
byte d0 = byteTranslator.decode (buffer[ptr++]); byte d0 = byteTranslator.decode (inBuffer[inPtr++]);
byte d1 = byteTranslator.decode (buffer[ptr++]); byte d1 = byteTranslator.decode (inBuffer[inPtr++]);
// reassemble bytes // reassemble bytes
byte b0 = (byte) ((d0 & 0x3F) | ((d3 & 0x30) << 2)); byte b0 = (byte) ((d0 & 0x3F) | ((d3 & 0x30) << 2));
@ -42,19 +43,19 @@ public class DiskReaderGCR extends DiskReader
outBuffer[outPtr++] = checksum (b0, checksums, 0, 2); outBuffer[outPtr++] = checksum (b0, checksums, 0, 2);
outBuffer[outPtr++] = checksum (b1, checksums, 2, 1); outBuffer[outPtr++] = checksum (b1, checksums, 2, 1);
if (j < 174) // get fourth disk byte if we are not at the very end if (j < 174) // get third byte if we are not at the very end
{ {
byte d2 = byteTranslator.decode (buffer[ptr++]); // translate byte d2 = byteTranslator.decode (inBuffer[inPtr++]); // translate
byte b2 = (byte) ((d2 & 0x3F) | ((d3 & 0x03) << 6)); // reassemble byte b2 = (byte) ((d2 & 0x3F) | ((d3 & 0x03) << 6)); // reassemble
outBuffer[outPtr++] = checksum (b2, checksums, 1, 0); // checksum outBuffer[outPtr++] = checksum (b2, checksums, 1, 0); // checksum
} }
} }
// decode four disk bytes into three data bytes // decode four disk bytes into three data bytes
byte d3 = byteTranslator.decode (buffer[ptr++]); // composite byte byte d3 = byteTranslator.decode (inBuffer[inPtr++]); // composite byte
byte d0 = byteTranslator.decode (buffer[ptr++]); byte d0 = byteTranslator.decode (inBuffer[inPtr++]);
byte d1 = byteTranslator.decode (buffer[ptr++]); byte d1 = byteTranslator.decode (inBuffer[inPtr++]);
byte d2 = byteTranslator.decode (buffer[ptr++]); byte d2 = byteTranslator.decode (inBuffer[inPtr++]);
// reassemble bytes // reassemble bytes
byte b0 = (byte) ((d0 & 0x3F) | ((d3 & 0x30) << 2)); byte b0 = (byte) ((d0 & 0x3F) | ((d3 & 0x30) << 2));
@ -71,19 +72,19 @@ public class DiskReaderGCR extends DiskReader
} }
// ---------------------------------------------------------------------------------// // ---------------------------------------------------------------------------------//
private byte checksum (byte b, int[] checksums, int c1, int c2) private byte checksum (byte diskByte, int[] checksums, int current, int next)
// ---------------------------------------------------------------------------------// // ---------------------------------------------------------------------------------//
{ {
int val = (b ^ checksums[c1]) & 0xFF; int val = (diskByte ^ checksums[current]) & 0xFF;
checksums[c2] += val; checksums[next] += val; // prepare next checksum
if (checksums[c1] > 0xFF) if (checksums[current] > 0xFF) // is there a carry?
{ {
++checksums[c2]; ++checksums[next]; // pass it on
checksums[c1] &= 0xFF; checksums[current] &= 0xFF; // back to 8 bits
} }
return (byte) val; return (byte) val; // converted data byte
} }
// ---------------------------------------------------------------------------------// // ---------------------------------------------------------------------------------//