method

sum

v1_9_1_378 - Show latest stable - Class: String

sum(p1 = v1)

public

Returns a basic n-bit checksum of the characters in str, where n is the optional Fixnum parameter, defaulting to 16. The result is simply the sum of the binary value of each character in str modulo 2n - 1. This is not a particularly good checksum.

static VALUE
rb_str_sum(int argc, VALUE *argv, VALUE str)
{
    VALUE vbits;
    int bits;
    char *ptr, *p, *pend;
    long len;

    if (argc == 0) {
        bits = 16;
    }
    else {
        rb_scan_args(argc, argv, "01", &vbits);
        bits = NUM2INT(vbits);
    }
    ptr = p = RSTRING_PTR(str);
    len = RSTRING_LEN(str);
    pend = p + len;
    if (bits >= sizeof(long)*CHAR_BIT) {
        VALUE sum = INT2FIX(0);

        while (p < pend) {
            str_mod_check(str, ptr, len);
            sum = rb_funcall(sum, '+', 1, INT2FIX((unsigned char)*p));
            p++;
        }
        if (bits != 0) {
            VALUE mod;

            mod = rb_funcall(INT2FIX(1), rb_intern("<<"), 1, INT2FIX(bits));
            mod = rb_funcall(mod, '-', 1, INT2FIX(1));
            sum = rb_funcall(sum, '&', 1, mod);
        }
        return sum;
    }
    else {
       unsigned long sum = 0;

        while (p < pend) {
            str_mod_check(str, ptr, len);
            sum += (unsigned char)*p;
            p++;
        }
        if (bits != 0) {
           sum &= (((unsigned long)1)<<bits)-1;
        }
        return rb_int2inum(sum);
    }
}

sum

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