pngunpack.c

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#include <stdio.h>
#include <stdlib.h>
#include "grib2.h"
 
int dec_png(unsigned char *, g2int *, g2int *, char *);
 
g2int
pngunpack(unsigned char *cpack, g2int len, g2int *idrstmpl, g2int ndpts,
          g2float *fld)
{
    g2int *ifld;
    g2int j, nbits, width, height;
    g2float ref, bscale, dscale;
    unsigned char *ctemp;
 
    rdieee(idrstmpl, &ref, 1);
    bscale = int_power(2.0, idrstmpl[1]);
    dscale = int_power(10.0, -idrstmpl[2]);
    nbits = idrstmpl[3];
 
    /* If nbits equals 0, we have a constant field where the reference
     * value is the data value at each gridpoint. */
    if (nbits != 0)
    {
        ifld = calloc(ndpts, sizeof(g2int));
        ctemp = calloc(ndpts * 4, 1);
        if (!ifld || !ctemp)
        {
            fprintf(stderr,"Could not allocate space in jpcunpack.\n  Data field NOT upacked.\n");
            return(1);
        }
        dec_png(cpack, &width, &height, ctemp);
        gbits(ctemp, ifld, 0, nbits, 0, ndpts);
        for (j = 0; j < ndpts; j++)
            fld[j] = (((g2float)ifld[j] * bscale) + ref) * dscale;
        free(ctemp);
        free(ifld);
    }
    else
    {
        for (j = 0; j < ndpts; j++)
            fld[j] = ref;
    }
 
    return(0);
}