Beispiel #1
0
// Conversion type-checks the conversion T(x).
// The result is in x.
func (check *Checker) conversion(x *operand, T Type) {
	constArg := x.mode == constant

	var ok bool
	switch {
	case constArg && isConstType(T):
		// constant conversion
		switch t := T.Underlying().(*Basic); {
		case representableConst(x.val, check.conf, t.kind, &x.val):
			ok = true
		case isInteger(x.typ) && isString(t):
			codepoint := int64(-1)
			if i, ok := exact.Int64Val(x.val); ok {
				codepoint = i
			}
			// If codepoint < 0 the absolute value is too large (or unknown) for
			// conversion. This is the same as converting any other out-of-range
			// value - let string(codepoint) do the work.
			x.val = exact.MakeString(string(codepoint))
			ok = true
		}
	case x.convertibleTo(check.conf, T):
		// non-constant conversion
		x.mode = value
		ok = true
	}

	if !ok {
		check.errorf(x.pos(), "cannot convert %s to %s", x, T)
		x.mode = invalid
		return
	}

	// The conversion argument types are final. For untyped values the
	// conversion provides the type, per the spec: "A constant may be
	// given a type explicitly by a constant declaration or conversion,...".
	final := x.typ
	if isUntyped(x.typ) {
		final = T
		// - For conversions to interfaces, use the argument's default type.
		// - For conversions of untyped constants to non-constant types, also
		//   use the default type (e.g., []byte("foo") should report string
		//   not []byte as type for the constant "foo").
		// - Keep untyped nil for untyped nil arguments.
		if IsInterface(T) || constArg && !isConstType(T) {
			final = defaultType(x.typ)
		}
		check.updateExprType(x.expr, final, true)
	}

	x.typ = T
}
Beispiel #2
0
// Int64 returns the numeric value of this constant truncated to fit
// a signed 64-bit integer.
//
func (c *Const) Int64() int64 {
	switch x := c.Value; x.Kind() {
	case exact.Int:
		if i, ok := exact.Int64Val(x); ok {
			return i
		}
		return 0
	case exact.Float:
		f, _ := exact.Float64Val(x)
		return int64(f)
	}
	panic(fmt.Sprintf("unexpected constant value: %T", c.Value))
}
Beispiel #3
0
func (check *Checker) arrayLength(e ast.Expr) int64 {
	var x operand
	check.expr(&x, e)
	if x.mode != constant {
		if x.mode != invalid {
			check.errorf(x.pos(), "array length %s must be constant", &x)
		}
		return 0
	}
	if !x.isInteger() {
		check.errorf(x.pos(), "array length %s must be integer", &x)
		return 0
	}
	n, ok := exact.Int64Val(x.val)
	if !ok || n < 0 {
		check.errorf(x.pos(), "invalid array length %s", &x)
		return 0
	}
	return n
}
Beispiel #4
0
// index checks an index expression for validity.
// If max >= 0, it is the upper bound for index.
// If index is valid and the result i >= 0, then i is the constant value of index.
func (check *Checker) index(index ast.Expr, max int64) (i int64, valid bool) {
	var x operand
	check.expr(&x, index)
	if x.mode == invalid {
		return
	}

	// an untyped constant must be representable as Int
	check.convertUntyped(&x, Typ[Int])
	if x.mode == invalid {
		return
	}

	// the index must be of integer type
	if !isInteger(x.typ) {
		check.invalidArg(x.pos(), "index %s must be integer", &x)
		return
	}

	// a constant index i must be in bounds
	if x.mode == constant {
		if exact.Sign(x.val) < 0 {
			check.invalidArg(x.pos(), "index %s must not be negative", &x)
			return
		}
		i, valid = exact.Int64Val(x.val)
		if !valid || max >= 0 && i >= max {
			check.errorf(x.pos(), "index %s is out of bounds", &x)
			return i, false
		}
		// 0 <= i [ && i < max ]
		return i, true
	}

	return -1, true
}
Beispiel #5
0
// representableConst reports whether x can be represented as
// value of the given basic type kind and for the configuration
// provided (only needed for int/uint sizes).
//
// If rounded != nil, *rounded is set to the rounded value of x for
// representable floating-point values; it is left alone otherwise.
// It is ok to provide the addressof the first argument for rounded.
func representableConst(x exact.Value, conf *Config, as BasicKind, rounded *exact.Value) bool {
	switch x.Kind() {
	case exact.Unknown:
		return true

	case exact.Bool:
		return as == Bool || as == UntypedBool

	case exact.Int:
		if x, ok := exact.Int64Val(x); ok {
			switch as {
			case Int:
				var s = uint(conf.sizeof(Typ[as])) * 8
				return int64(-1)<<(s-1) <= x && x <= int64(1)<<(s-1)-1
			case Int8:
				const s = 8
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int16:
				const s = 16
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int32:
				const s = 32
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int64:
				return true
			case Uint, Uintptr:
				if s := uint(conf.sizeof(Typ[as])) * 8; s < 64 {
					return 0 <= x && x <= int64(1)<<s-1
				}
				return 0 <= x
			case Uint8:
				const s = 8
				return 0 <= x && x <= 1<<s-1
			case Uint16:
				const s = 16
				return 0 <= x && x <= 1<<s-1
			case Uint32:
				const s = 32
				return 0 <= x && x <= 1<<s-1
			case Uint64:
				return 0 <= x
			case Float32, Float64, Complex64, Complex128,
				UntypedInt, UntypedFloat, UntypedComplex:
				return true
			}
		}

		n := exact.BitLen(x)
		switch as {
		case Uint, Uintptr:
			var s = uint(conf.sizeof(Typ[as])) * 8
			return exact.Sign(x) >= 0 && n <= int(s)
		case Uint64:
			return exact.Sign(x) >= 0 && n <= 64
		case Float32, Complex64:
			if rounded == nil {
				return fitsFloat32(x)
			}
			r := roundFloat32(x)
			if r != nil {
				*rounded = r
				return true
			}
		case Float64, Complex128:
			if rounded == nil {
				return fitsFloat64(x)
			}
			r := roundFloat64(x)
			if r != nil {
				*rounded = r
				return true
			}
		case UntypedInt, UntypedFloat, UntypedComplex:
			return true
		}

	case exact.Float:
		switch as {
		case Float32, Complex64:
			if rounded == nil {
				return fitsFloat32(x)
			}
			r := roundFloat32(x)
			if r != nil {
				*rounded = r
				return true
			}
		case Float64, Complex128:
			if rounded == nil {
				return fitsFloat64(x)
			}
			r := roundFloat64(x)
			if r != nil {
				*rounded = r
				return true
			}
		case UntypedFloat, UntypedComplex:
			return true
		}

	case exact.Complex:
		switch as {
		case Complex64:
			if rounded == nil {
				return fitsFloat32(exact.Real(x)) && fitsFloat32(exact.Imag(x))
			}
			re := roundFloat32(exact.Real(x))
			im := roundFloat32(exact.Imag(x))
			if re != nil && im != nil {
				*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
				return true
			}
		case Complex128:
			if rounded == nil {
				return fitsFloat64(exact.Real(x)) && fitsFloat64(exact.Imag(x))
			}
			re := roundFloat64(exact.Real(x))
			im := roundFloat64(exact.Imag(x))
			if re != nil && im != nil {
				*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
				return true
			}
		case UntypedComplex:
			return true
		}

	case exact.String:
		return as == String || as == UntypedString

	default:
		unreachable()
	}

	return false
}