diff options
Diffstat (limited to 'src/libserialize/serialize.rs')
| -rw-r--r-- | src/libserialize/serialize.rs | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/src/libserialize/serialize.rs b/src/libserialize/serialize.rs index cf948078b08..d53891828f1 100644 --- a/src/libserialize/serialize.rs +++ b/src/libserialize/serialize.rs @@ -723,10 +723,17 @@ macro_rules! peel { ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* }) } -/// Evaluates to the number of identifiers passed to it, for example: `count_idents!(a, b, c) == 3 -macro_rules! count_idents { - () => { 0 }; - ($_i:ident, $($rest:ident,)*) => { 1 + count_idents!($($rest,)*) } +/// Evaluates to the number of tokens passed to it. +/// +/// Logarithmic counting: every one or two recursive expansions, the number of +/// tokens to count is divided by two, instead of being reduced by one. +/// Therefore, the recursion depth is the binary logarithm of the number of +/// tokens to count, and the expanded tree is likewise very small. +macro_rules! count { + () => (0usize); + ($one:tt) => (1usize); + ($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize); + ($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize); } macro_rules! tuple { @@ -735,7 +742,7 @@ macro_rules! tuple { impl<$($name:Decodable),*> Decodable for ($($name,)*) { #[allow(non_snake_case)] fn decode<D: Decoder>(d: &mut D) -> Result<($($name,)*), D::Error> { - let len: usize = count_idents!($($name,)*); + let len: usize = count!($($name)*); d.read_tuple(len, |d| { let mut i = 0; let ret = ($(d.read_tuple_arg({ i+=1; i-1 }, |d| -> Result<$name, D::Error> { |