package ij.io;
/**
* A class for reading arbitrary numbers of bits from a byte array.
* @author Eric Kjellman egkjellman at wisc.edu
*/
public class BitBuffer {
private int currentByte;
private int currentBit;
private byte[] byteBuffer;
private int eofByte;
private int[] backMask;
private int[] frontMask;
private boolean eofFlag;
public BitBuffer(byte[] byteBuffer) {
this.byteBuffer = byteBuffer;
currentByte = 0;
currentBit = 0;
eofByte = byteBuffer.length;
backMask = new int[] {0x0000, 0x0001, 0x0003, 0x0007,
0x000F, 0x001F, 0x003F, 0x007F};
frontMask = new int[] {0x0000, 0x0080, 0x00C0, 0x00E0,
0x00F0, 0x00F8, 0x00FC, 0x00FE};
}
public int getBits(int bitsToRead) {
if (bitsToRead == 0)
return 0;
if (eofFlag)
return -1; // Already at end of file
int toStore = 0;
while(bitsToRead != 0 && !eofFlag) {
if (bitsToRead >= 8 - currentBit) {
if (currentBit == 0) { // special
toStore = toStore << 8;
int cb = ((int) byteBuffer[currentByte]);
toStore += (cb<0 ? (int) 256 + cb : (int) cb);
bitsToRead -= 8;
currentByte++;
} else {
toStore = toStore << (8 - currentBit);
toStore += ((int) byteBuffer[currentByte]) & backMask[8 - currentBit];
bitsToRead -= (8 - currentBit);
currentBit = 0;
currentByte++;
}
} else {
toStore = toStore << bitsToRead;
int cb = ((int) byteBuffer[currentByte]);
cb = (cb<0 ? (int) 256 + cb : (int) cb);
toStore += ((cb) & (0x00FF - frontMask[currentBit])) >> (8 - (currentBit + bitsToRead));
currentBit += bitsToRead;
bitsToRead = 0;
}
if (currentByte == eofByte) {
eofFlag = true;
return toStore;
}
}
return toStore;
}
}
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