UT/UT_BitStream.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 * Produced by:
 *      Jeff Lait
 *      Side Effects Software Inc
 *      477 Richmond Street West
 *      Toronto, Ontario
 *      Canada   M5V 3E7
 *      416-504-9876
 *
 * NAME:        UT_BitStream.h ( UT Library, C++)
 *
 * COMMENTS: This allows you to read and write from binary
 *      buffers on a per bit basis.  It can handle up to 32bit
 *      reads or writes.
 */

#ifndef __UT_BitStream__
#define __UT_BitStream__

#include "UT_API.h"

#include "UT_IntArray.h"

class UT_String;
class UT_WorkBuffer;

class UT_API UT_BitStream
{
public:
    UT_BitStream();
    UT_BitStream(int nbits);
    virtual ~UT_BitStream();

    // Delete & reset the buffer.
    void                 clear();

    int                  getLen() const;
    unsigned int        *getBuf() const { return myBuf; }
    void                 setBuf(unsigned int *buf, int len);

    int                  getBitLength() const   { return myBitLength; }

    // Note that the write/read head is shared, so it is not proper
    // to try and write and read to the same buffer.
    // You can write to the buffer, do a reset, and then read, however.
    // Just be careful you don't try to read past the end or you'll assert.
    void                 write(int val, int bits);
    int                  read(int bits);        // Read, sign extended
    unsigned             uread(int bits);       // Read, zero extended

    // Seek nbits into the stream.   When:
    //  whence[0] -- Seek from beginning of stream
    //  whence[1] -- Seek from current location
    //  whence[2] -- Seek from end of stream
    int                  seek(int nbits, int whence = 0);
    int                  tell() const;
    int                  rewind() { return seek(0, 0); }

    //
    // All the save methods take a number of "words" to process.  The number of
    // bits per word is defined by the method.  For example, saveToHex() has a
    // word-size of 4 bits.  This may be counter intuitive, but that's how it
    // works.
    // The offset parameter determines how many BITS into the stream to start
    // reading from when generating the string.
    //

    // Load from a hexidecimal string or generate a hex string
    // (word size = 4 bits)
    void                 loadFromHex(const char *hex);
    void                 saveToHex(UT_String &result, int nwords=-1,
                                                      int offset=0);
    void                 saveToHex(UT_WorkBuffer &result, int nwords=-1,
                                                      int offset=0);

    // Load or save a 6-bit encoded string
    // (word size = 6 bits)
    void                 loadFrom6Bit(const char *data);
    void                 saveTo6Bit(UT_String &result, int nwords=-1,
                                                        int offset=0);
    void                 saveTo6Bit(UT_WorkBuffer &result, int nwords=-1,
                                                        int offset=0);

    // Load or save a 8-bit encoded string.  Note that the binary data
    // may not be handled correctly since nulls can be inserted into the
    // UT_String (and are considered terminators).
    // (word size = 8 bits)
    void                 loadFromByte(const char *data);
    void                 saveToByte(UT_String &result, int nwords=-1,
                                                        int offset=0);
    // Load or save a 8-bit encoded buffer. These are used for the binary
    // data so that it handles the nulls within the data.
    void                 loadFromByte(const char *data, int nwords);
    int                  saveToByte(unsigned char *data, int nwords, 
                                                        int offset=0);

    // Initialize from a penta string.  If failed, returns non-zero
    // Also initializes the errors array to the start and end character
    // of each penta which failed.
    // A penta is 5 character sequense delimitted by non-alnum chars.
    // Each one stores 20 bits of data and has a 5 bits of checksum data.
    int                  loadFromPenta(const char *penta, UT_IntArray &errors);
    // Write out the penta, only using the preferred characters.
    void                 saveToPenta(UT_String &result, int nwords=-1,
                                                        int offset=0);

protected:
    // Load a single penta word.
    int                  loadPenta(const char *penta);
    int                  padTo(int nbits, int max, int off, int &savelen);
    void                 popPad(int savelen)
                         {
                             myBitLength = savelen;
                             seek(0, 2);        // Seek to end of file again
                         }
    
    // Local data.
    unsigned int        *myBuf;                 // The buffer to read bits from
    int                  myHard;                // Whether we own the buffer.
    int                  myBitOff, myWordOff;   // The seek position
    int                  myBitLength;           // Total written length
    int                  mySize;                // Allocated size
};

#endif

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