Method: BigDecimal#power

Defined in:
bigdecimal.c

- (Object) power

power(n) power(n, prec)

Returns the value raised to the power of n.

Note that n must be an Integer.

Also available as the operator **



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# File 'bigdecimal.c', line 2188

static VALUE
BigDecimal_power(int argc, VALUE*argv, VALUE self)
{
    ENTER(5);
    VALUE vexp, prec;
    Real* exp = NULL;
    Real *x, *y;
    ssize_t mp, ma, n;
    SIGNED_VALUE int_exp;
    double d;

    rb_scan_args(argc, argv, "11", &vexp, &prec);

    GUARD_OBJ(x, GetVpValue(self, 1));
    n = NIL_P(prec) ? (ssize_t)(x->Prec*VpBaseFig()) : NUM2SSIZET(prec);

    if (VpIsNaN(x)) {
	y = VpCreateRbObject(n, "0#");
	RB_GC_GUARD(y->obj);
	VpSetNaN(y);
	return ToValue(y);
    }

  retry:
    switch (TYPE(vexp)) {
      case T_FIXNUM:
	break;

      case T_BIGNUM:
	break;

      case T_FLOAT:
	d = RFLOAT_VALUE(vexp);
	if (d == round(d)) {
	    if (FIXABLE(d)) {
		vexp = LONG2FIX((long)d);
	    }
	    else {
		vexp = rb_dbl2big(d);
	    }
	    goto retry;
	}
	exp = GetVpValueWithPrec(vexp, DBL_DIG+1, 1);
	break;

      case T_RATIONAL:
	if (is_zero(RRATIONAL(vexp)->num)) {
	    if (is_positive(vexp)) {
		vexp = INT2FIX(0);
		goto retry;
	    }
	}
	else if (is_one(RRATIONAL(vexp)->den)) {
	    vexp = RRATIONAL(vexp)->num;
	    goto retry;
	}
	exp = GetVpValueWithPrec(vexp, n, 1);
	break;

      case T_DATA:
	if (is_kind_of_BigDecimal(vexp)) {
	    VALUE zero = INT2FIX(0);
	    VALUE rounded = BigDecimal_round(1, &zero, vexp);
	    if (RTEST(BigDecimal_eq(vexp, rounded))) {
		vexp = BigDecimal_to_i(vexp);
		goto retry;
	    }
	    exp = DATA_PTR(vexp);
	    break;
	}
	/* fall through */
      default:
	rb_raise(rb_eTypeError,
		 "wrong argument type %s (expected scalar Numeric)",
		 rb_obj_classname(vexp));
    }

    if (VpIsZero(x)) {
	if (is_negative(vexp)) {
	    y = VpCreateRbObject(n, "#0");
	    RB_GC_GUARD(y->obj);
	    if (VpGetSign(x) < 0) {
		if (is_integer(vexp)) {
		    if (is_even(vexp)) {
			/* (-0) ** (-even_integer)  -> Infinity */
			VpSetPosInf(y);
		    }
		    else {
			/* (-0) ** (-odd_integer)  -> -Infinity */
			VpSetNegInf(y);
		    }
		}
		else {
		    /* (-0) ** (-non_integer)  -> Infinity */
		    VpSetPosInf(y);
		}
	    }
	    else {
		/* (+0) ** (-num)  -> Infinity */
		VpSetPosInf(y);
	    }
	    return ToValue(y);
	}
	else if (is_zero(vexp)) {
	    return ToValue(VpCreateRbObject(n, "1"));
	}
	else {
	    return ToValue(VpCreateRbObject(n, "0"));
	}
    }

    if (is_zero(vexp)) {
	return ToValue(VpCreateRbObject(n, "1"));
    }
    else if (is_one(vexp)) {
	return self;
    }

    if (VpIsInf(x)) {
	if (is_negative(vexp)) {
	    if (VpGetSign(x) < 0) {
		if (is_integer(vexp)) {
		    if (is_even(vexp)) {
			/* (-Infinity) ** (-even_integer) -> +0 */
			return ToValue(VpCreateRbObject(n, "0"));
		    }
		    else {
			/* (-Infinity) ** (-odd_integer) -> -0 */
			return ToValue(VpCreateRbObject(n, "-0"));
		    }
		}
		else {
		    /* (-Infinity) ** (-non_integer) -> -0 */
		    return ToValue(VpCreateRbObject(n, "-0"));
		}
	    }
	    else {
		return ToValue(VpCreateRbObject(n, "0"));
	    }
	}
	else {
	    y = VpCreateRbObject(n, "0#");
	    if (VpGetSign(x) < 0) {
		if (is_integer(vexp)) {
		    if (is_even(vexp)) {
			VpSetPosInf(y);
		    }
		    else {
			VpSetNegInf(y);
		    }
		}
		else {
		    /* TODO: support complex */
		    rb_raise(rb_eMathDomainError,
			     "a non-integral exponent for a negative base");
		}
	    }
	    else {
		VpSetPosInf(y);
	    }
	    return ToValue(y);
	}
    }

    if (exp != NULL) {
	return rmpd_power_by_big_decimal(x, exp, n);
    }
    else if (RB_TYPE_P(vexp, T_BIGNUM)) {
	VALUE abs_value = BigDecimal_abs(self);
	if (is_one(abs_value)) {
	    return ToValue(VpCreateRbObject(n, "1"));
	}
	else if (RTEST(rb_funcall(abs_value, '<', 1, INT2FIX(1)))) {
	    if (is_negative(vexp)) {
		y = VpCreateRbObject(n, "0#");
		if (is_even(vexp)) {
		    VpSetInf(y, VpGetSign(x));
		}
		else {
		    VpSetInf(y, -VpGetSign(x));
		}
		return ToValue(y);
	    }
	    else if (VpGetSign(x) < 0 && is_even(vexp)) {
		return ToValue(VpCreateRbObject(n, "-0"));
	    }
	    else {
		return ToValue(VpCreateRbObject(n, "0"));
	    }
	}
	else {
	    if (is_positive(vexp)) {
		y = VpCreateRbObject(n, "0#");
		if (is_even(vexp)) {
		    VpSetInf(y, VpGetSign(x));
		}
		else {
		    VpSetInf(y, -VpGetSign(x));
		}
		return ToValue(y);
	    }
	    else if (VpGetSign(x) < 0 && is_even(vexp)) {
		return ToValue(VpCreateRbObject(n, "-0"));
	    }
	    else {
		return ToValue(VpCreateRbObject(n, "0"));
	    }
	}
    }

    int_exp = FIX2LONG(vexp);
    ma = int_exp;
    if (ma <  0) ma = -ma;
    if (ma == 0) ma = 1;

    if (VpIsDef(x)) {
	mp = x->Prec * (VpBaseFig() + 1);
	GUARD_OBJ(y, VpCreateRbObject(mp * (ma + 1), "0"));
    }
    else {
	GUARD_OBJ(y, VpCreateRbObject(1, "0"));
    }
    VpPower(y, x, int_exp);
    if (!NIL_P(prec) && VpIsDef(y)) {
	VpMidRound(y, VpGetRoundMode(), n);
    }
    return ToValue(y);
}

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