83 lines
2.8 KiB
C
Executable file
83 lines
2.8 KiB
C
Executable file
#include <stdio.h>
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#include <stdlib.h>
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#include "grib2.h"
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void seekgb(FILE *lugb,g2int iseek,g2int mseek,g2int *lskip,g2int *lgrib)
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//$$$ SUBPROGRAM DOCUMENTATION BLOCK
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//
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// SUBPROGRAM: seekgb Searches a file for the next GRIB message.
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// PRGMMR: Gilbert ORG: W/NP11 DATE: 2002-10-28
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//
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// ABSTRACT: This subprogram searches a file for the next GRIB Message.
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// The search is done starting at byte offset iseek of the file referenced
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// by lugb for mseek bytes at a time.
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// If found, the starting position and length of the message are returned
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// in lskip and lgrib, respectively.
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// The search is terminated when an EOF or I/O error is encountered.
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//
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// PROGRAM HISTORY LOG:
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// 2002-10-28 GILBERT Modified from Iredell's skgb subroutine
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// 2009-01-16 VUONG Changed lskip to 4 instead of sizof(g2int)
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//
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// USAGE: seekgb(FILE *lugb,g2int iseek,g2int mseek,int *lskip,int *lgrib)
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// INPUT ARGUMENTS:
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// lugb - FILE pointer for the file to search. File must be
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// opened before this routine is called.
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// iseek - number of bytes in the file to skip before search
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// mseek - number of bytes to search at a time
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// OUTPUT ARGUMENTS:
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// lskip - number of bytes to skip from the beggining of the file
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// to where the GRIB message starts
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// lgrib - number of bytes in message (set to 0, if no message found)
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//
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// ATTRIBUTES:
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// LANGUAGE: C
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//
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//$$$
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{
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g2int ret;
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g2int k,k4,ipos,nread,lim,start,vers,lengrib;
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int end;
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unsigned char *cbuf;
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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*lgrib=0;
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cbuf=(unsigned char *)malloc(mseek);
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nread=mseek;
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ipos=iseek;
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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// LOOP UNTIL GRIB MESSAGE IS FOUND
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while (*lgrib==0 && nread==mseek) {
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// READ PARTIAL SECTION
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ret=fseek(lugb,ipos,SEEK_SET);
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nread=fread(cbuf,sizeof(unsigned char),mseek,lugb);
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lim=nread-8;
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// LOOK FOR 'GRIB...' IN PARTIAL SECTION
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for (k=0;k<lim;k++) {
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gbit(cbuf,&start,(k+0)*8,4*8);
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gbit(cbuf,&vers,(k+7)*8,1*8);
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if (start==1196575042 && (vers==1 || vers==2)) {
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// LOOK FOR '7777' AT END OF GRIB MESSAGE
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if (vers == 1) gbit(cbuf,&lengrib,(k+4)*8,3*8);
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if (vers == 2) gbit(cbuf,&lengrib,(k+12)*8,4*8);
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ret=fseek(lugb,ipos+k+lengrib-4,SEEK_SET);
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// Hard code to 4 instead of sizeof(g2int)
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k4=fread(&end,4,1,lugb);
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if (k4 == 1 && end == 926365495) { //GRIB message found
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*lskip=ipos+k;
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*lgrib=lengrib;
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break;
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}
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}
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}
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ipos=ipos+lim;
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}
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free(cbuf);
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}
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