workbench/libs/iffparse/readchunkrecords.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "iffparse_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11 #include <proto/iffparse.h>
  12
  13         AROS_LH4(LONG, ReadChunkRecords,
  14
  15 /*  SYNOPSIS */
  16         AROS_LHA(struct IFFHandle *, iff, A0),
  17         AROS_LHA(APTR              , buf, A1),
  18         AROS_LHA(LONG              , bytesPerRecord, D0),
  19         AROS_LHA(LONG              , numRecords, D1),
  20
  21 /*  LOCATION */
  22         struct Library *, IFFParseBase, 12, IFFParse)
  23
  24 /*  FUNCTION
  25         Read a number of records with the given size from the current chunk
  26         into a buffer. Attempts to read past the end of the chunk will be truncated.
  27
  28     INPUTS
  29          iff              - pointer to IFFHandle struct.
  30         buf              -  pointer to a buffer into which the data will be placed.
  31         bytesPerRecord  - number of bytes per record.
  32         numRecords      -  number of records to read.
  33
  34     RESULT
  35         actual -   (positive) the actual number of whole records read.
  36                   (negative) IFFERR_#? error code if not succesfull.
  37
  38
  39     NOTES
  40
  41     EXAMPLE
  42
  43     BUGS
  44
  45     SEE ALSO
  46         ReadChunkBytes(), ParseIFF(), WriteChunkRecords()
  47
  48     INTERNALS
  49
  50 *****************************************************************************/
  51 {
  52     AROS_LIBFUNC_INIT
  53
  54     struct ContextNode *cn;
  55
  56     LONG   bytestoread,
  57           lefttoread,
  58           bytesread;
  59
  60     DEBUG_READCHUNKRECORDS(dprintf("ReadChunkRecords: iff %p buf %p bytesPerRecord %ld numRecords %ld\n",
  61                                    iff, buf, bytesPerRecord, numRecords));
  62
  63     /* Get pointer to top contextnode */
  64     cn = TopChunk(iff);
  65
  66     lefttoread = cn->cn_Size - cn->cn_Scan;
  67
  68     bytestoread = bytesPerRecord * numRecords;
  69
  70     /* If bytestoread > lefttoread then we must truncate the readoperation */
  71     if (bytestoread > lefttoread)
  72     {
  73         bytestoread = lefttoread;
  74
  75
  76         /* See to it that we only read whole records */
  77         bytestoread -= (lefttoread % bytesPerRecord);
  78     }
  79
  80     /* Beware: bytestoread is 0 now if bytesPerRecord > lefttoread */
  81
  82     bytesread = ReadStream
  83     (
  84         iff,
  85         buf,
  86         bytestoread,
  87         IPB(IFFParseBase)
  88     );
  89
  90
  91     /* Return number of records  actually read (if no error occured)  */
  92     if (bytesread < 0)
  93         /* IFFERR_#? in bytesread */
  94         numRecords = bytesread;
  95     else
  96     {
  97         /* calculate the actual number of records written */
  98         numRecords = bytesread / bytesPerRecord;
  99
 100         /* Update number of bytes read */
 101         cn->cn_Scan += bytesread;
 102     }
 103
 104     DEBUG_READCHUNKRECORDS(dprintf("ReadChunkRecords: return %ld\n", numRecords));
 105     return (numRecords);
 106
 107     AROS_LIBFUNC_EXIT
 108 } /* ReadChunkRecords */