source: lmdz_wrf/WRFV3/external/io_grib1/WGRIB/missing.c @ 1

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

/*
 *  number of missing data points w. ebisuzaki
 *
 *  v1.1: just faster my dear
 *  v1.2: just faster my dear
 *
 */

static int bitsum[256] = {
    8, 7, 7, 6, 7, 6, 6, 5, 7, 6, 6, 5, 6, 5, 5, 4, 
    7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3, 
    7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1, 
    7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1, 
    6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2, 
    5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1, 
    5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1, 
    4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};


int missing_points(unsigned char *bitmap, int n) {

    int count;
    unsigned int tmp;
    if (bitmap == NULL) return 0;

    count = 0;
    while (n >= 8) {
        tmp = *bitmap++;
        n -= 8;
        count += bitsum[tmp];
    }
    tmp = *bitmap | ((1 << (8 - n)) - 1);
    count += bitsum[tmp];

    return count;
}