From 1246d4067fdc034d064dfb78f88c2c3c079c3f4f Mon Sep 17 00:00:00 2001 From: James Miller Date: Fri, 9 Jan 2015 16:10:57 +1300 Subject: Add `core::num::wrapping` and fix overflow errors. Many of the core rust libraries have places that rely on integer wrapping behaviour. These places have been altered to use the wrapping_* methods: * core::hash::sip - A number of macros * core::str - The `maximal_suffix` method in `TwoWaySearcher` * rustc::util::nodemap - Implementation of FnvHash * rustc_back::sha2 - A number of macros and other places * rand::isaac - Isaac64Rng, changed to use the Wrapping helper type Some places had "benign" underflow. This is when underflow or overflow occurs, but the unspecified value is not used due to other conditions. * collections::bit::Bitv - underflow when `self.nbits` is zero. * collections::hash::{map,table} - Underflow when searching an empty table. Did cause undefined behaviour in this case due to an out-of-bounds ptr::offset based on the underflowed index. However the resulting pointers would never be read from. * syntax::ext::deriving::encodable - Underflow when calculating the index of the last field in a variant with no fields. These cases were altered to avoid the underflow, often by moving the underflowing operation to a place where underflow could not happen. There was one case that relied on the fact that unsigned arithmetic and two's complement arithmetic are identical with wrapping semantics. This was changed to use the wrapping_* methods. Finally, the calculation of variant discriminants could overflow if the preceeding discriminant was `U64_MAX`. The logic in `rustc::middle::ty` for this was altered to avoid the overflow completely, while the remaining places were changed to use wrapping methods. This is because `rustc::middle::ty::enum_variants` now throws an error when the calculated discriminant value overflows a `u64`. This behaviour can be triggered by the following code: ``` enum Foo { A = U64_MAX, B } ``` This commit also implements the remaining integer operators for Wrapped. --- src/libstd/collections/hash/map.rs | 7 +++++++ src/libstd/collections/hash/table.rs | 6 +++++- 2 files changed, 12 insertions(+), 1 deletion(-) (limited to 'src/libstd/collections') diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs index faddbba5059..8eb29a8327a 100644 --- a/src/libstd/collections/hash/map.rs +++ b/src/libstd/collections/hash/map.rs @@ -314,6 +314,13 @@ fn search_hashed(table: M, M: Deref>, F: FnMut(&K) -> bool, { + // This is the only function where capacity can be zero. To avoid + // undefined behaviour when Bucket::new gets the raw bucket in this + // case, immediately return the appropriate search result. + if table.capacity() == 0 { + return TableRef(table); + } + let size = table.size(); let mut probe = Bucket::new(table, hash); let ib = probe.index(); diff --git a/src/libstd/collections/hash/table.rs b/src/libstd/collections/hash/table.rs index 4c03d8915eb..908b5267b69 100644 --- a/src/libstd/collections/hash/table.rs +++ b/src/libstd/collections/hash/table.rs @@ -224,6 +224,9 @@ impl>> Bucket { } pub fn at_index(table: M, ib_index: usize) -> Bucket { + // if capacity is 0, then the RawBucket will be populated with bogus pointers. + // This is an uncommon case though, so avoid it in release builds. + debug_assert!(table.capacity() > 0, "Table should have capacity at this point"); let ib_index = ib_index & (table.capacity() - 1); Bucket { raw: unsafe { @@ -368,10 +371,11 @@ impl>> FullBucket { /// In the cited blog posts above, this is called the "distance to /// initial bucket", or DIB. Also known as "probe count". pub fn distance(&self) -> usize { + use core::num::wrapping::WrappingOps; // Calculates the distance one has to travel when going from // `hash mod capacity` onwards to `idx mod capacity`, wrapping around // if the destination is not reached before the end of the table. - (self.idx - self.hash().inspect() as usize) & (self.table.capacity() - 1) + (self.idx.wrapping_sub(self.hash().inspect() as usize)) & (self.table.capacity() - 1) } #[inline] -- cgit 1.4.1-3-g733a5