external/io_grib1/MEL_grib1/gribgetbms.c

   1 /*  gribgetbms.c                June 17, 1996 by Alice Nakajima, SAIC   */
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>
   5 #include "dprints.h"            /* for dprints */
   6 #include "gribfuncs.h"          /* prototypes */
   7
   8 /*
   9 *
  10 ************************************************************************
  11 * A.  FUNCTION:   gribgetbms
  12 *       decode the Bitmap Section from the provided pointer location
  13 *       and store its info in the internal BMS structure.
  14 *       Pre-defined Bitmap case is not supported.
  15 *
  16 *    INTERFACE:
  17 *       int   gribgetbms ( curr_ptr, bms, gds_flag, ulGrid_size, errmsg)
  18 *
  19 *    ARGUMENTS (I=input, O=output, I&O=input and output):
  20 *      (I)   char *curr_ptr;
  21 *            pointer to location where Bitmap Section to decode is expected;
  22 *      (O)   BMS_INPUT *bms;
  23 *            pointer to empty BMS structure; will hold decoded BMS info;
  24 *      (I)   int gds_flag;
  25 *            flag set if GDS is present
  26 *      (I)   unsigned long ulGrid_size;
  27 *            size of grid as in Binary Data Section struct
  28 *      (O)   char *errmsg
  29 *            returned filled if error occurred;
  30 *
  31 *     RETURN CODE:
  32 *     0>  BMS info stored in BMS structure if not using pre-defined bitmap;
  33 *     1>  error, corrupted bms; msg in errmsg;
  34 ************************************************************************
  35 */
  36
  37 #if PROTOTYPE_NEEDED
  38 int   gribgetbms ( char *curr_ptr, BMS_INPUT *bms, int gds_flag,
  39                 unsigned long ulGrid_size, char *errmsg)
  40 #else
  41 int   gribgetbms (curr_ptr, bms, gds_flag, ulGrid_size, errmsg)
  42                 char *curr_ptr;
  43                 BMS_INPUT *bms;
  44                 int gds_flag;
  45                 unsigned long ulGrid_size;
  46                 char *errmsg;
  47 #endif
  48 {
  49   char *func= "gribgetbms";
  50   char  *pp;
  51   int totbits,val, bitpos,stopbit;  /* tmp working vars */
  52   unsigned long SectLength;       /* message and section size */
  53   unsigned long ulvar;              /* tmp var */
  54   unsigned long skip=0;
  55
  56 /*
  57 *
  58 * A.0      INIT Status to no error
  59 */
  60 int   status=0;
  61
  62      DPRINT0 ("Entering gribgetbms():\n");
  63 /*
  64 *
  65 * A.1      FUNCTION gbyte   !get bitmap length
  66 */
  67     skip=0;
  68     gbyte(curr_ptr,(unsigned long *)&SectLength,&skip,24);
  69     DPRINT0 ("SectLength\n");
  70     bms->uslength= (unsigned long) SectLength;
  71
  72 /*
  73 *
  74 * A.2      FUNCTION gbyte   !get number of unused bits
  75 */
  76     gbyte(curr_ptr,&ulvar,&skip,8);
  77     DPRINT0 ("bms->usUnused_bits\n");
  78     bms->usUnused_bits= (unsigned short) ulvar;
  79
  80 /*
  81 *
  82 * A.3      FUNCTION gbyte   !get bitmap id (non-zero for a pre-defined bitmap)
  83 */
  84     gbyte(curr_ptr,&ulvar,&skip,16);
  85     DPRINT0 ("bms->usBMS_id\n");
  86     bms->usBMS_id= (unsigned short) ulvar;
  87
  88 /*
  89 *
  90 * A.4      IF (Bitmap follows)   !not a predefined bitmap
  91 */
  92     if ( bms->uslength > 6)     /* Bitmap follows */
  93        {
  94
  95 /*
  96 * A.4.1       CALCULATE Num of bits in bitmap
  97 */
  98          /* = (BMS length)*8 bits - 48 header bits - # of unsused bits */
  99          totbits=SectLength*8 - 48 - bms->usUnused_bits;
 100
 101 /*
 102 * A.4.2       IF (GDS is present AND
 103 *                      #bits differs from Grid Size)        !Corrupted BMS
 104 *                 RETURN 1
 105 *             ENDIF
 106 */
 107           if (gds_flag && totbits != ulGrid_size) {
 108                 DPRINT3( "%s: corrupted BMS, gds_flag set but "\
 109                 "totbits %d != ulgrid_sz %d\n"
 110                 , func, totbits, ulGrid_size);
 111
 112                 sprintf(errmsg, "%s: corrupted BMS, gds_flag set but "\
 113                 "totbits %d != ulgrid_sz %d\n" , func, totbits, ulGrid_size);
 114                 status=  (1); /* Corrupted BMS */
 115                 goto BYE;
 116                 }
 117
 118 /*
 119 * A.4.3       ASSIGN bitmap pointer to 6th byte of BMS
 120 */
 121           bms->bit_map =  curr_ptr + 6;
 122           pp= bms->bit_map;
 123           bms->ulbits_set= 0;
 124 /*
 125 *
 126 * A.4.4       !SUM up total number of bits set
 127 *             FOR (Each 8-bit block of Total Bits Present in BMS)
 128 */
 129           for ( ; totbits > 0 ; totbits-=8)
 130           {
 131 /*
 132 * A.4.4.1       IF (any of the 8 bits are set)
 133 */
 134              if ((val=(int)*pp++) != 0)
 135                {
 136
 137 /*
 138 * A.4.4.1.1        IF (not within 8 bits of end of bitmap)
 139 *                      SET stopbit to 0
 140 *                  ELSE
 141 *                      SET stopbit to end of bitmap
 142 *                  ENDIF
 143 */
 144                  if (totbits > 8) stopbit=0;   /* check all 8 bits */
 145                  else stopbit= 7-totbits+1;    /* stop at end of bitmap */
 146
 147 /*
 148 * A.4.4.1.2        SUM up number of bits set in this BMS byte
 149 */
 150                  for (bitpos= 7; bitpos >= stopbit; bitpos--)
 151                     if (val >> bitpos & 0x0001) bms->ulbits_set += 1;
 152 /*
 153 * A.4.4.1       ENDIF  ! any of 8 exists
 154 */
 155                }
 156 /*
 157 * A.4.4     ENDFOR   !each 8-bit loop
 158 */
 159            }
 160 /*
 161 * A.4      ENDIF        !Bitmap follows
 162 */
 163         }
 164
 165 /*  else {
 166         / * Predefined Bitmap - not supported!! Could add function here
 167             to load a bitmap from local storage * /
 168          bms->uslength=6;
 169          bms->bit_map= Load_predefined_bms (bms->usBMS_id);
 170        }
 171 */
 172
 173
 174 BYE:
 175 /*
 176 *
 177 * A.5     DEBUG Print
 178 *
 179 * A.6     RETURN Status
 180 */
 181     DPRINT2 ("Exiting %s, Status=%d;\n", func, status);
 182     return (status);
 183 /*
 184 * END OF FUNCTION
 185 */
 186 }