/*
 * Sum bytes in file mod 2^16
 */
#include <stdio.h>
#include <stdlib.h>

main(argc,argv)
char **argv;
{
    register unsigned sum;
    register i, c;
    register FILE *f;
    register long nbytes;
    int errflg = 0;

    i = 1;
    do {
        if(i < argc) {
            if ((f = fopen(argv[i], "r")) == NULL) {
                fprintf(stderr, "sum: Can't open %s\n", argv[i]);
                errflg += 10;
                continue;
            }
        } else
            f = stdin;
        sum = 0;
        nbytes = 0;
        while ((c = getc(f)) != EOF) {
            nbytes++;
            if (sum&01)
                sum = (sum>>1) + 0x8000;
            else
                sum >>= 1;
            sum += c;
            sum &= 0xFFFF;
        }
        if (ferror(f)) {
            errflg++;
            fprintf(stderr, "sum: read error on %s\n", argc>1?argv[i]:"-");
        }
        printf("%05u%6ld", sum, (nbytes+BUFSIZ-1)/BUFSIZ);
        if(argc > 2)
            printf(" %s", argv[i]);
        printf("\n");
        fclose(f);
    } while(++i < argc);
    exit(errflg);
}
