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Returns the integer square root of the non-negative integer n, which is the largest non-negative integer less than or equal to the square root of numeric.
Integer.sqrt(0)       # => 0
Integer.sqrt(1)       # => 1
Integer.sqrt(24)      # => 4
Integer.sqrt(25)      # => 5
Integer.sqrt(10**400) # => 10**200
If numeric is not an Integer, it is converted to an Integer:
Integer.sqrt(Complex(4, 0))  # => 2
Integer.sqrt(Rational(4, 1)) # => 2
Integer.sqrt(4.0)            # => 2
Integer.sqrt(3.14159)        # => 1
This method is equivalent to Math.sqrt(numeric).floor, except that the result of the latter code may differ from the true value due to the limited precision of floating point arithmetic.
Integer.sqrt(10**46)    # => 100000000000000000000000
Math.sqrt(10**46).floor # => 99999999999999991611392
Raises an exception if numeric is negative.
 
               static VALUE
rb_int_s_isqrt(VALUE self, VALUE num)
{
    unsigned long n, sq;
    num = rb_to_int(num);
    if (FIXNUM_P(num)) {
        if (FIXNUM_NEGATIVE_P(num)) {
            domain_error("isqrt");
        }
        n = FIX2ULONG(num);
        sq = rb_ulong_isqrt(n);
        return LONG2FIX(sq);
    }
    else {
        size_t biglen;
        if (RBIGNUM_NEGATIVE_P(num)) {
            domain_error("isqrt");
        }
        biglen = BIGNUM_LEN(num);
        if (biglen == 0) return INT2FIX(0);
#if SIZEOF_BDIGIT <= SIZEOF_LONG
        /* short-circuit */
        if (biglen == 1) {
            n = BIGNUM_DIGITS(num)[0];
            sq = rb_ulong_isqrt(n);
            return ULONG2NUM(sq);
        }
#endif
        return rb_big_isqrt(num);
    }
}
            

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