// Uint64 returns the numeric value of this constant truncated to fit
// an unsigned 64-bit integer.
//
func (c *Const) Uint64() uint64 {
switch x := c.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 constant value: %T", c.Value))
}
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 || !representableConst(x.val, nil, UntypedInt, nil)) {
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 {
// rhs must be within reasonable bounds
const stupidShift = 1023 - 1 + 52 // so we can express smallestFloat64
s, ok := exact.Uint64Val(y.val)
if !ok || s > stupidShift {
check.invalidOp(y.pos(), "stupid shift count %s", y)
x.mode = invalid
return
}
// The lhs is representable as an integer but may not be an integer
// (e.g., 2.0, an untyped float) - this can only happen for untyped
// non-integer numeric constants. Correct the type so that the shift
// result is of integer type.
if !isInteger(x.typ) {
x.typ = Typ[UntypedInt]
}
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.".
//
// 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.
info, found := check.untyped[x.expr]
assert(found)
info.isLhs = true
check.untyped[x.expr] = info
// keep x's type
x.mode = value
return
}
}
// constant rhs must be >= 0
if y.mode == constant && exact.Sign(y.val) < 0 {
check.invalidOp(y.pos(), "shift count %s must not be negative", y)
}
// 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
}
x.mode = value
}