workbench/libs/iffparse/readchunkrecords.c

   1 /*
   2     Copyright © 1995-2016, 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 successful.
  37
  38     NOTES
  39
  40     EXAMPLE
  41
  42     BUGS
  43
  44     SEE ALSO
  45         ReadChunkBytes(), ParseIFF(), WriteChunkRecords()
  46
  47     INTERNALS
  48
  49 *****************************************************************************/
  50 {
  51     AROS_LIBFUNC_INIT
  52
  53     struct ContextNode *cn;
  54
  55     LONG   bytestoread,
  56           lefttoread,
  57           bytesread;
  58
  59     DEBUG_READCHUNKRECORDS(dprintf("ReadChunkRecords: iff %p buf %p bytesPerRecord %ld numRecords %ld\n",
  60                                    iff, buf, bytesPerRecord, numRecords));
  61
  62     /* Get pointer to top contextnode */
  63     cn = TopChunk(iff);
  64
  65     lefttoread = cn->cn_Size - cn->cn_Scan;
  66
  67     bytestoread = bytesPerRecord * numRecords;
  68
  69     /* If bytestoread > lefttoread then we must truncate the readoperation */
  70     if (bytestoread > lefttoread)
  71     {
  72         bytestoread = lefttoread;
  73
  74
  75         /* See to it that we only read whole records */
  76         bytestoread -= (lefttoread % bytesPerRecord);
  77     }
  78
  79     /* Beware: bytestoread is 0 now if bytesPerRecord > lefttoread */
  80
  81     bytesread = ReadStream
  82     (
  83         iff,
  84         buf,
  85         bytestoread,
  86         IPB(IFFParseBase)
  87     );
  88
  89
  90     /* Return number of records  actually read (if no error occured)  */
  91     if (bytesread < 0)
  92         /* IFFERR_#? in bytesread */
  93         numRecords = bytesread;
  94     else
  95     {
  96         /* calculate the actual number of records written */
  97         numRecords = bytesread / bytesPerRecord;
  98
  99         /* Update number of bytes read */
 100         cn->cn_Scan += bytesread;
 101     }
 102
 103     DEBUG_READCHUNKRECORDS(dprintf("ReadChunkRecords: return %ld\n", numRecords));
 104     return (numRecords);
 105
 106     AROS_LIBFUNC_EXIT
 107 } /* ReadChunkRecords */