Kernel

Returns the \BigDecimal converted from +value+
with a precision of +ndigits+ decimal digits.

When +ndigits+ is less than the number of significant digits
in the value, the result is rounded to that number of digits,
according to the current rounding mode; see BigDecimal.mode.

Returns value converted to a BigDecimal, depending on the type of value:

• Integer, Float, Rational, Complex, or BigDecimal: converted directly:

  # Integer, Complex, or BigDecimal value does not require ndigits; ignored if given.
  BigDecimal(2)                     # => 0.2e1
  BigDecimal(Complex(2, 0))         # => 0.2e1
  BigDecimal(BigDecimal(2))         # => 0.2e1
  # Float or Rational value requires ndigits.
  BigDecimal(2.0, 0)                # => 0.2e1
  BigDecimal(Rational(2, 1), 0)     # => 0.2e1
  

• String: converted by parsing if it contains an integer or floating-point literal; leading and trailing whitespace is ignored:

  # String does not require ndigits; ignored if given.
  BigDecimal('2')     # => 0.2e1
  BigDecimal('2.0')   # => 0.2e1
  BigDecimal('0.2e1') # => 0.2e1
  BigDecimal(' 2.0 ') # => 0.2e1
  

• Other type that responds to method :to_str: first converted to a string, then converted to a BigDecimal, as above.

• Other type:

  • Raises an exception if keyword argument exception is true.

  • Returns nil if keyword argument exception is true.

Raises an exception if value evaluates to a Float and digits is larger than Float::DIG + 1.

 
               static VALUE
f_BigDecimal(int argc, VALUE *argv, VALUE self)
{
    VALUE val, digs_v, opts = Qnil;
    argc = rb_scan_args(argc, argv, "11:", &val, &digs_v, &opts);
    int exception = opts_exception_p(opts);

    size_t digs = SIZE_MAX; /* this means digs is omitted */
    if (argc > 1) {
        digs_v = rb_to_int(digs_v);
        if (FIXNUM_P(digs_v)) {
            long n = FIX2LONG(digs_v);
            if (n < 0)
                goto negative_digs;
            digs = (size_t)n;
        }
        else {
            if (RBIGNUM_NEGATIVE_P(digs_v)) {
              negative_digs:
                if (!exception)
                    return Qnil;
                rb_raise(rb_eArgError, "negative precision");
            }
            digs = NUM2SIZET(digs_v);
        }
    }

    return rb_convert_to_BigDecimal(val, digs, exception);
}