method

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v2_2_9 - Show latest stable - 0 notes - Class: Bignum

[](p1) public

Bit Reference—Returns the nth bit in the (assumed) binary representation of big, where big[0] is the least significant bit.

a = 9**15
50.downto(0) do |n|
  print a[n]
end

produces:

000101110110100000111000011110010100111100010111001

Show source

static VALUE
rb_big_aref(VALUE x, VALUE y)
{
    BDIGIT *xds;
    size_t shift;
    size_t i, s1, s2;
    long l;
    BDIGIT bit;

    if (RB_BIGNUM_TYPE_P(y)) {
        if (!BIGNUM_SIGN(y))
            return INT2FIX(0);
        bigtrunc(y);
        if (BIGSIZE(y) > sizeof(size_t)) {
          out_of_range:
            return BIGNUM_SIGN(x) ? INT2FIX(0) : INT2FIX(1);
        }
#if SIZEOF_SIZE_T <= SIZEOF_LONG
        shift = big2ulong(y, "long");
#else
        shift = big2ull(y, "long long");
#endif
    }
    else {
        l = NUM2LONG(y);
        if (l < 0) return INT2FIX(0);
        shift = (size_t)l;
    }
    s1 = shift/BITSPERDIG;
    s2 = shift%BITSPERDIG;
    bit = (BDIGIT)1 << s2;

    if (s1 >= BIGNUM_LEN(x)) goto out_of_range;

    xds = BDIGITS(x);
    if (BIGNUM_POSITIVE_P(x))
        return (xds[s1] & bit) ? INT2FIX(1) : INT2FIX(0);
    if (xds[s1] & (bit-1))
        return (xds[s1] & bit) ? INT2FIX(0) : INT2FIX(1);
    for (i = 0; i < s1; i++)
        if (xds[i])
            return (xds[s1] & bit) ? INT2FIX(0) : INT2FIX(1);
    return (xds[s1] & bit) ? INT2FIX(1) : INT2FIX(0);
}

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