1                 : #include <stdio.h>
       2                 : #include <stdlib.h>
       3                 : #include "grib2.h"
       4                 : 
       5               0 : void seekgb(FILE *lugb,g2int iseek,g2int mseek,g2int *lskip,g2int *lgrib)
       6                 : //$$$  SUBPROGRAM DOCUMENTATION BLOCK
       7                 : //
       8                 : // SUBPROGRAM: seekgb         Searches a file for the next GRIB message.
       9                 : //   PRGMMR: Gilbert          ORG: W/NP11      DATE: 2002-10-28
      10                 : //
      11                 : // ABSTRACT: This subprogram searches a file for the next GRIB Message.
      12                 : //   The search is done starting at byte offset iseek of the file referenced 
      13                 : //   by lugb for mseek bytes at a time.
      14                 : //   If found, the starting position and length of the message are returned
      15                 : //   in lskip and lgrib, respectively.
      16                 : //   The search is terminated when an EOF or I/O error is encountered.
      17                 : //
      18                 : // PROGRAM HISTORY LOG:
      19                 : // 2002-10-28  GILBERT   Modified from Iredell's skgb subroutine
      20                 : //
      21                 : // USAGE:    seekgb(FILE *lugb,g2int iseek,g2int mseek,int *lskip,int *lgrib)
      22                 : //   INPUT ARGUMENTS:
      23                 : //     lugb       - FILE pointer for the file to search.  File must be
      24                 : //                  opened before this routine is called.
      25                 : //     iseek      - number of bytes in the file to skip before search
      26                 : //     mseek      - number of bytes to search at a time
      27                 : //   OUTPUT ARGUMENTS:
      28                 : //     lskip      - number of bytes to skip from the beggining of the file
      29                 : //                  to where the GRIB message starts
      30                 : //     lgrib      - number of bytes in message (set to 0, if no message found)
      31                 : //
      32                 : // ATTRIBUTES:
      33                 : //   LANGUAGE: C
      34                 : //
      35                 : //$$$
      36                 : {
      37                 :       g2int  ret;
      38                 :       g2int k,k4,ipos,nread,lim,start,vers,end,lengrib;
      39                 :       unsigned char *cbuf;
      40                 : 
      41                 : // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      42               0 :       *lgrib=0;
      43               0 :       cbuf=(unsigned char *)malloc(mseek);
      44               0 :       nread=mseek;
      45               0 :       ipos=iseek;
      46                 : 
      47                 : // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      48                 : //  LOOP UNTIL GRIB MESSAGE IS FOUND
      49                 : 
      50               0 :       while (*lgrib==0 && nread==mseek) {
      51                 : 
      52                 : //  READ PARTIAL SECTION
      53                 : 
      54               0 :         ret=fseek(lugb,ipos,SEEK_SET);
      55               0 :         nread=fread(cbuf,sizeof(unsigned char),mseek,lugb);
      56               0 :         lim=nread-8;
      57                 : 
      58                 : //  LOOK FOR 'GRIB...' IN PARTIAL SECTION
      59                 : 
      60               0 :         for (k=0;k<lim;k++) {
      61               0 :           gbit(cbuf,&start,(k+0)*8,4*8);
      62               0 :           gbit(cbuf,&vers,(k+7)*8,1*8);
      63               0 :           if (start==1196575042 && (vers==1 || vers==2)) {
      64                 : //  LOOK FOR '7777' AT END OF GRIB MESSAGE
      65               0 :             if (vers == 1) gbit(cbuf,&lengrib,(k+4)*8,3*8);
      66               0 :             if (vers == 2) gbit(cbuf,&lengrib,(k+12)*8,4*8);
      67               0 :             ret=fseek(lugb,ipos+k+lengrib-4,SEEK_SET);
      68               0 :             k4=fread(&end,sizeof(g2int),1,lugb);
      69               0 :             if (k4 == 1 && end == 926365495) {      //GRIB message found
      70               0 :                 *lskip=ipos+k;
      71               0 :                 *lgrib=lengrib;
      72               0 :                 break;
      73                 :             }
      74                 :           }
      75                 :         }
      76               0 :         ipos=ipos+lim;
      77                 :       }
      78                 : 
      79               0 :       free(cbuf);
      80               0 : }