#include <stdio.h>
#include <stdlib.h>
#include "grib2.h"

g2int g2_unpack6(unsigned char *cgrib,g2int *iofst,g2int ngpts,g2int *ibmap,
               g2int **bmap)
//$$$  SUBPROGRAM DOCUMENTATION BLOCK
//                .      .    .                                       .
// SUBPROGRAM:    g2_unpack6 
//   PRGMMR: Gilbert         ORG: W/NP11    DATE: 2002-10-31
//
// ABSTRACT: This subroutine unpacks Section 6 (Bit-Map Section)
//           as defined in GRIB Edition 2.
//
// PROGRAM HISTORY LOG:
// 2002-10-31  Gilbert
//
// USAGE:    int g2_unpack6(unsigned char *cgrib,g2int *iofst,g2int ngpts,
//                          g2int *ibmap,g2int **bmap)
//   INPUT ARGUMENTS:
//     cgrib    - char array containing Section 6 of the GRIB2 message
//     iofst    - Bit offset of the beginning of Section 6 in cgrib.
//     ngpts    - Number of grid points specified in the bit-map
//
//   OUTPUT ARGUMENTS:      
//     iofst    - Bit offset at the end of Section 6, returned.
//     ibmap    - Bitmap indicator ( see Code Table 6.0 )
//                0 = bitmap applies and is included in Section 6.
//                1-253 = Predefined bitmap applies
//                254 = Previously defined bitmap applies to this field
//                255 = Bit map does not apply to this product.
//     bmap     - Pointer to an integer array containing decoded bitmap. 
//                ( if ibmap=0 )
//
//   RETURN VALUES:
//     ierr     - Error return code.
//                0 = no error
//                2 = Not Section 6
//                4 = Unrecognized pre-defined bit-map.
//                6 = memory allocation error
//
// REMARKS: None
//
// ATTRIBUTES:
//   LANGUAGE: C
//   MACHINE:
//
//$$$//
{
      g2int j,ierr,isecnum;
      g2int *lbmap=0;
      g2int *intbmap;

      ierr=0;
      *bmap=0;    //NULL

      *iofst=*iofst+32;    // skip Length of Section
      gbit(cgrib,&isecnum,*iofst,8);         // Get Section Number
      *iofst=*iofst+8; 

      if ( isecnum != 6 ) {
         ierr=2;
         fprintf(stderr,"g2_unpack6: Not Section 6 data.\n");
         return(ierr);
      }

      gbit(cgrib,ibmap,*iofst,8);    // Get bit-map indicator
      *iofst=*iofst+8;

      if (*ibmap == 0) {               // Unpack bitmap
         if (ngpts > 0) lbmap=(g2int *)calloc(ngpts,sizeof(g2int));
         if (lbmap == 0) {
            ierr=6;
            return(ierr);
         }
         *bmap=lbmap;

         intbmap=(g2int *)calloc(ngpts,sizeof(g2int));
         gbits(cgrib,intbmap,*iofst,1,0,ngpts);
         *iofst=*iofst+ngpts;
         for (j=0;j<ngpts;j++) {
           lbmap[j]=(g2int)intbmap[j];
         }
         free(intbmap);
//      else if (*ibmap.eq.254)               ! Use previous bitmap
//        return(ierr);
//      else if (*ibmap.eq.255)               ! No bitmap in message
//        bmap(1:ngpts)=.true.
//      else {
//        print *,'gf_unpack6: Predefined bitmap ',*ibmap,' not recognized.'
//        ierr=4;
      }
      
      return(ierr);    // End of Section 6 processing

}
