#include <stdio.h>

#include <stdlib.h>

#include "grib2.h"

g2int g2_unpack1(unsigned char *cgrib,g2int *iofst,g2int **ids,g2int *idslen)

/*//$$$  SUBPROGRAM DOCUMENTATION BLOCK

//                .      .    .                                       .

// SUBPROGRAM:    g2_unpack1

//   PRGMMR: Gilbert         ORG: W/NP11    DATE: 2002-10-29

//

// ABSTRACT: This subroutine unpacks Section 1 (Identification Section)

//           as defined in GRIB Edition 2.

//

// PROGRAM HISTORY LOG:

// 2002-10-29  Gilbert

//

// USAGE:    int g2_unpack1(unsigned char *cgrib,g2int *iofst,g2int **ids,

//                          g2int *idslen)

//   INPUT ARGUMENTS:

//     cgrib    - char array containing Section 1 of the GRIB2 message

//     iofst    - Bit offset for the beginning of Section 1 in cgrib.

//

//   OUTPUT ARGUMENTS:

//     iofst    - Bit offset at the end of Section 1, returned.

//     ids      - address of pointer to integer array containing information

//                read from Section 1, the Identification section.

//            ids[0]  = Identification of originating Centre

//                                 ( see Common Code Table C-1 )

//            ids[1]  = Identification of originating Sub-centre

//            ids[2]  = GRIB Master Tables Version Number

//                                 ( see Code Table 1.0 )

//            ids[3]  = GRIB Local Tables Version Number

//                                 ( see Code Table 1.1 )

//            ids[4]  = Significance of Reference Time (Code Table 1.2)

//            ids[5]  = Year ( 4 digits )

//            ids[6]  = Month

//            ids[7]  = Day

//            ids[8]  = Hour

//            ids[9]  = Minute

//            ids[10]  = Second

//            ids[11]  = Production status of processed data

//                                 ( see Code Table 1.3 )

//            ids[12]  = Type of processed data ( see Code Table 1.4 )

//     idslen   - Number of elements in ids[].

//

//   RETURN VALUES:

//     ierr     - Error return code.

//                0 = no error

//                2 = Array passed is not section 1

//                6 = memory allocation error

//

// REMARKS:

//

// ATTRIBUTES:

//   LANGUAGE: C

//   MACHINE:

//

//$$$

*/

{

      g2int i,lensec,nbits,ierr,isecnum = 0;

      g2int mapid[13]={2,2,1,1,1,2,1,1,1,1,1,1,1};

      ierr=0;

      *idslen=13;

      *ids=0;

      gbit(cgrib,&lensec,*iofst,32);        // Get Length of Section

      *iofst=*iofst+32;

      gbit(cgrib,&isecnum,*iofst,8);         // Get Section Number

      *iofst=*iofst+8;

      if ( isecnum != 1 ) {

         ierr=2;

         *idslen=13;

         fprintf(stderr,"g2_unpack1: Not Section 1 data.\n");

         return(ierr);

      }

      //

      //   Unpack each value into array ids from the

      //   the appropriate number of octets, which are specified in

      //   corresponding entries in array mapid.

      //

      *ids=(g2int *)calloc(*idslen,sizeof(g2int));

      if (*ids == 0) {

         ierr=6;

         return(ierr);

      }

      for (i=0;i<*idslen;i++) {

        nbits=mapid[i]*8;

        gbit(cgrib,*ids+i,*iofst,nbits);

        *iofst=*iofst+nbits;

      }

      return(ierr);    // End of Section 1 processing

}