示例#1
0
// Uint64 returns the numeric value of this literal truncated to fit
// an unsigned 64-bit integer.
//
func (l *Literal) Uint64() uint64 {
	switch x := l.Value; x.Kind() {
	case exact.Int:
		if u, ok := exact.Uint64Val(x); ok {
			return u
		}
		return 0
	case exact.Float:
		f, _ := exact.Float64Val(x)
		return uint64(f)
	}
	panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
}
示例#2
0
func (check *checker) shift(x, y *operand, op token.Token) {
	untypedx := isUntyped(x.typ)

	// The lhs must be of integer type or be representable
	// as an integer; otherwise the shift has no chance.
	if !isInteger(x.typ) && (!untypedx || !isRepresentableConst(x.val, nil, UntypedInt)) {
		check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
		x.mode = invalid
		return
	}

	// spec: "The right operand in a shift expression must have unsigned
	// integer type or be an untyped constant that can be converted to
	// unsigned integer type."
	switch {
	case isInteger(y.typ) && isUnsigned(y.typ):
		// nothing to do
	case isUntyped(y.typ):
		check.convertUntyped(y, Typ[UntypedInt])
		if y.mode == invalid {
			x.mode = invalid
			return
		}
	default:
		check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
		x.mode = invalid
		return
	}

	if x.mode == constant {
		if y.mode == constant {
			if untypedx {
				x.typ = Typ[UntypedInt]
			}
			// rhs must be within reasonable bounds
			const stupidShift = 1024
			s, ok := exact.Uint64Val(y.val)
			if !ok || s >= stupidShift {
				check.invalidOp(y.pos(), "%s: stupid shift", y)
				x.mode = invalid
				return
			}
			// everything's ok
			x.val = exact.Shift(x.val, op, uint(s))
			return
		}

		// non-constant shift with constant lhs
		if untypedx {
			// spec: "If the left operand of a non-constant shift expression is
			// an untyped constant, the type of the constant is what it would be
			// if the shift expression were replaced by its left operand alone;
			// the type is int if it cannot be determined from the context (for
			// instance, if the shift expression is an operand in a comparison
			// against an untyped constant)".

			// Delay operand checking until we know the final type:
			// The lhs expression must be in the untyped map, mark
			// the entry as lhs shift operand.
			if info, ok := check.untyped[x.expr]; ok {
				info.isLhs = true
				check.untyped[x.expr] = info
			} else {
				unreachable()
			}
			// keep x's type
			x.mode = value
			return
		}
	}

	// non-constant shift - lhs must be an integer
	if !isInteger(x.typ) {
		check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
		x.mode = invalid
		return
	}

	// non-constant shift
	x.mode = value
}