[GPS]: libbzip2 provides easy compression and decompression.  For a project I was working on I needed the ability to compress header files that contained large files converted to hex.  
The little extension below is what I used.  It doesn't have the ability to load normal .bz2 files, 
because it uses a simple format of uncompressedDataLength\0data.  Still it's quite useful.

It could be used to compress large amounts of data before sending over a network, and a lot of other things.

Use it however you want (just don't sue me).
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**Code**

  #include <stdio.h>
  #include <stdlib.h>
  #include "bzip2-1.0.2/bzlib.h"
  #include "tcl.h"
  
  
  #define OBJ_CMD_ARGS (ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[])
  
  int BZ2CompressCmd OBJ_CMD_ARGS {
    Tcl_Obj *result;
    unsigned char *inputData;
    int inputLength;
    char *tmp;
    unsigned int tmpSize = 0;
    /* 1 - 9; 9 gives the best compression but uses the most runtime memory*/
    int blockSize = 9;
    /*1 - 4; 4 gives the most diagnostic info*/
    int verbosity = 0;
    /*30 is suggested; see docs for bzip2 for full info*/
    int workFactor = 30;
    int headerOffset;
  
    if (objc != 2) {
      Tcl_WrongNumArgs (interp, 1, objv, "dataToCompress");
      return TCL_ERROR;
    }
  
  
    inputData = Tcl_GetByteArrayFromObj (objv[1], &inputLength);
    /*The bzip2 documentation says inputLength + %1 + 600 bytes*/
    /* + 40 for the length header*/
    tmpSize = (inputLength / 100 + inputLength + 600 + 40);
    
    tmp = ckalloc (tmpSize);
  
    sprintf (tmp, "%d", inputLength);
  
    /*+ 1 for NUL*/
    headerOffset = (strlen (tmp) + 1);
    
    if (BZ2_bzBuffToBuffCompress (&tmp[headerOffset], &tmpSize, (char *) inputData, inputLength,
      blockSize, verbosity, workFactor
    ) != BZ_OK) {
      ckfree (tmp);
      Tcl_SetResult (interp, "compression failed", TCL_STATIC);
      return TCL_ERROR;
    }
    
    /*The BZ2 function sets tmpSize to the new size, but it doesn't know about our header.*/
    result = Tcl_NewByteArrayObj ((unsigned char *)tmp, (int )tmpSize + headerOffset);
    
    fprintf (stdout, "compressed %d to %d bytes\n", inputLength, (tmpSize + headerOffset));
  
    ckfree (tmp);
    
    Tcl_SetObjResult (interp, result);
    
    return TCL_OK;
  }
  
  int BZ2DecompressCmd OBJ_CMD_ARGS {
    int compDataLength;
    char *compData;
    int headerOffset;
    unsigned int decompLength = 0;
    char *decompData;
    int verbosity = 0;
    Tcl_Obj *result;
  
    if (objc != 2) {
      Tcl_WrongNumArgs (interp, 1, objv, "dataToDecompress");
      return TCL_ERROR;
    }
  
    compData = (char *) Tcl_GetByteArrayFromObj (objv[1], &compDataLength);
    
    decompLength = atoi (compData);
    headerOffset = (strlen (compData) + 1);
    
    decompData = ckalloc (decompLength); 
  
    if (BZ2_bzBuffToBuffDecompress (decompData, &decompLength, &compData[headerOffset], 
      (compDataLength - headerOffset), 0, verbosity
    ) != BZ_OK) {
      ckfree (decompData);
      Tcl_SetResult (interp, "compression failed", TCL_STATIC);
      return TCL_ERROR;
    }
  
    result = Tcl_NewByteArrayObj ((unsigned char *)decompData, decompLength);
  
    ckfree (decompData);
  
    Tcl_SetObjResult (interp, result);
  
    return TCL_OK;
  }
  
  
  int Bz2_Init (Tcl_Interp *interp) {
    #define OBJ_CMD(name,func) Tcl_CreateObjCommand(interp,name,func, (ClientData) NULL, (Tcl_CmdDeleteProc *) NULL)
  
    OBJ_CMD ("bz2:compress", BZ2CompressCmd);
    OBJ_CMD ("bz2:decompress", BZ2DecompressCmd);
  
    #undef OBJ_CMD
      
    return TCL_OK;
  }
  
  #undef OBJ_CMD_ARGS
  
----

**Usage**

 set compData [bz2:compress $hugeString]

 set decompData [bz2:decompress $compData]
 
simple eh?

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!!!!!!
%| [Category Package] | [Category Compression] |%
!!!!!!