gcr_4b5b.c

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/*
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *  Copyright 2006 Wolfgang Moser (http://d81.de)
 *
 */

#define DBG_USERMODE

#define DBG_PROGNAME "OPENCBM.DLL"

#include "debug.h"

#define DLL
#include "opencbm.h"

#include <stddef.h>

int CBMAPIDECL
gcr_5_to_4_decode(const unsigned char *source, unsigned char *dest,
                  size_t sourceLength,         size_t destLength)
{
    int rv;

    FUNC_ENTER();

    DBG_ASSERT( (source != NULL )     && (sourceLength  > 0) );
    DBG_ASSERT( (dest   != NULL )     && (destLength    > 0) );
    DBG_ASSERT( (dest < (source + 2)) || (dest > (source+4)) );

    if (sourceLength < 5)
    {
        DBG_WARN((DBG_PREFIX "*** source buffer is less than 5 bytes, only partial decoding done!"));
    }
    if (destLength < 4)
    {
        DBG_WARN((DBG_PREFIX "*** destination buffer is less than 4 bytes, only partial decoding done!"));
    }

    if( (source == NULL) || (dest == NULL) || (sourceLength<=0) )
    {
        rv = -1;
    }
    else
    {
        int i;

            /* 255 denotes illegal GCR bytes, for error checking extensions */
        static const unsigned char decodeGCR[32] =
            {255,255,255,255,255,255,255,255,255,  8,  0,  1,255, 12,  4,  5,
             255,255,  2,  3,255, 15,  6,  7,255,  9, 10, 11,255, 13, 14,255 };

            /* at least 24 bits for shifting into bits 16...20 */
        register unsigned int tdest, nybble;

        rv = 0;

        tdest   = *source;
        tdest <<= 13;

        for(i = 5; (i < 13) && (destLength > 0); i += 2, dest++, destLength--)
        {
            source++, sourceLength--;
            if(sourceLength > 0)
            {
                tdest  |= ((unsigned int)(*source)) << i;
            }
            else
            {
                    // no more input available, because GCR bytes
                    // with value 0 are not defined. But this must
                    // only be done, if at least one sourcebyte is
                    // already missing
                if ( 0 == ((tdest >> 16) & 0x3ff) ) break;
            }

                // "tdest >> 16" could be optimized to a word
                // aligned access, hopefully the compiler does
                // this for us (in a portable way)
            nybble  = decodeGCR[ (tdest >> 16) & 0x1f ];
            if(nybble > 15) rv |= 2;    // invalid GCR detected
            *dest   = nybble << 4;
            tdest <<= 5;

            nybble  = decodeGCR[ (tdest >> 16) & 0x1f ];
            if(nybble > 15) rv |= 1;    // invalid GCR detected
            *dest  |= (nybble & 0x0f);
            tdest <<= 5;

            rv    <<= 2;    // mark invalid GCR codes, make room for new
        }

    }

    FUNC_LEAVE_INT(rv);
    return rv;
}

int CBMAPIDECL
gcr_4_to_5_encode(const unsigned char *source, unsigned char *dest,
                  size_t sourceLength,         size_t destLength)
{
    int rv;

    FUNC_ENTER();

    DBG_ASSERT( (source !=   NULL ) && (sourceLength  > 0) );
    DBG_ASSERT( (dest   !=   NULL ) && (destLength    > 0) );
    DBG_ASSERT( (dest   <= source ) || (dest > (source+3)) );

    if (sourceLength < 4)
    {
        DBG_WARN((DBG_PREFIX "*** source buffer is less than 4 bytes, only partial decoding done!"));
    }
    if (destLength < 5)
    {
        DBG_WARN((DBG_PREFIX "*** destination buffer is less than 5 bytes, only partial decoding done!"));
    }

    if( (source == NULL) || (dest == NULL) || (sourceLength<=0) )
    {
        rv = -1;
    }
    else
    {
        static const unsigned char encodeGCR[16] =
            { 10, 11, 18, 19, 14, 15, 22, 23, 9, 25, 26, 27, 13, 29, 30, 21 };
        int i;
            /* at least 16 bits for overflow shifting */
        register unsigned int tdest = 0;

        rv = 0;

        for( i  = 2;
            (i < 10) && (sourceLength > 0) && (destLength > 0);
             i += 2, source++, sourceLength--, dest++, destLength--)
        {
            tdest <<= 5;  /* make room for the upper nybble */
            tdest  |= encodeGCR[ (*source) >>   4 ];

            tdest <<= 5;  /* make room for the lower nybble */
            tdest  |= encodeGCR[ (*source) & 0x0f ];

            *dest   = (unsigned char)(tdest >> i);
        }

        // (i == 10), if the loop exited normally
        if(destLength > 0)
        {
            // There're bits in the line, either because it is the
            // last one with bits from 0...7 or because the source
            // buffer got to its end and the remaining bits could
            // be written out partially.

            *dest = ((unsigned char)(tdest)) << ((10-i) & 0x07);
        }
    }

    FUNC_LEAVE_INT(rv);
    return rv;
}