g2_info.c

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#include <stdio.h>
#include <stdlib.h>
#include "grib2_int.h"
 
g2int
g2_info(unsigned char *cgrib, g2int *listsec0, g2int *listsec1,
        g2int *numfields, g2int *numlocal)
{
    g2int mapsec1len = 13;
    g2int mapsec1[13] = {2, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1};
    g2int i, j, istart, iofst, lengrib, lensec0, lensec1;
    g2int ipos, isecnum, nbits, lensec;
 
    *numlocal = 0;
    *numfields = 0;
 
    /*  Check for beginning of GRIB message in the first 100 bytes. */
    istart = -1;
    for (j = 0; j < 100; j++)
    {
        if (cgrib[j] == 'G' && cgrib[j + 1] == 'R' && cgrib[j + 2] == 'I' &&
            cgrib[j + 3] == 'B')
        {
            istart = j;
            break;
        }
    }
    if (istart == -1)
    {
        printf("g2_info:  Beginning characters GRIB not found.");
        return G2_INFO_NO_GRIB;
    }
 
    /*  Unpack Section 0 - Indicator Section. */
    iofst = 8 * (istart + 6);
    gbit(cgrib, listsec0, iofst, 8);     /* Discipline */
    iofst = iofst + 8;
    gbit(cgrib, listsec0 + 1, iofst, 8);     /* GRIB edition number */
    iofst = iofst + 8;
    iofst = iofst + 32;
    gbit(cgrib, &lengrib, iofst, 32);        /* Length of GRIB message */
    iofst = iofst + 32;
    listsec0[2] = lengrib;
    lensec0 = 16;
    ipos = istart + lensec0;
 
    /*  Currently handles only GRIB Edition 2. */
    if (listsec0[1] != 2)
    {
        printf("g2_info: can only decode GRIB edition 2.");
        return G2_INFO_GRIB_VERSION;
    }
 
    /*  Unpack Section 1 - Identification Section */
    gbit(cgrib, &lensec1, iofst, 32);        /* Length of Section 1 */
    iofst = iofst + 32;
    gbit(cgrib, &isecnum, iofst, 8);         /* Section number (1) */
    iofst = iofst + 8;
    if (isecnum != 1)
    {
        printf("g2_info: Could not find section 1.");
        return G2_INFO_NO_SEC1;
    }
 
    /* Unpack each input value in array listsec1 into the
       appropriate number of octets, which are specified in
       corresponding entries in array mapsec1. */
    for (i = 0; i < mapsec1len; i++)
    {
        nbits = mapsec1[i] * 8;
        gbit(cgrib, listsec1 + i, iofst, nbits);
        iofst = iofst + nbits;
    }
    ipos = ipos + lensec1;
 
    /*  Loop through the remaining sections to see if they are
     *  valid. Also count the number of times Section 2 and Section
     *  4 appear. */
    for (;;)
    {
        if (cgrib[ipos] == '7' && cgrib[ipos + 1] == '7' && cgrib[ipos + 2] == '7' &&
            cgrib[ipos + 3] == '7')
        {
            ipos = ipos + 4;
            if (ipos != (istart + lengrib))
            {
                printf("g2_info: '7777' found, but not where expected.\n");
                return G2_INFO_WRONG_END;
            }
            break;
        }
 
        iofst = ipos * 8;
        gbit(cgrib, &lensec, iofst, 32);        /* Get Length of Section */
        iofst = iofst + 32;
        gbit(cgrib, &isecnum, iofst, 8);         /* Get Section number */
        iofst = iofst + 8;
        ipos = ipos + lensec;                 /* Update beginning of section pointer */
        if (ipos > (istart + lengrib))
        {
            printf("g2_info: '7777'  not found at end of GRIB message.\n");
            return G2_INFO_BAD_END;
        }
        if (isecnum >= 2 && isecnum <= 7)
        {
            /* Increment counter for total number of local sections
             * or fields found. */
            if (isecnum == 2)
                (*numlocal)++;
            else if (isecnum == 4)
                (*numfields)++;
        }
        else
        {
            printf("g2_info: Invalid section number found in GRIB message: %ld\n", isecnum);
            return G2_INFO_INVAL_SEC;
        }
    }
 
    return 0;
}