libstd: modify wrong shift width #6108
Merged
+39
−21
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
borrow = *elem << (uint::bits - n_bits); The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand, because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture. If `--opt-level` option is not given to rustc, the code above runs as if the right operand is `(uint::bits - n_bits) % 32`, but if --opt-level is given, `borrow` is always zero. I wonder why this bug is not catched in the libstd's testsuite (I try the `rustc --test --opt-level=2 bigint.rs` before fixing the bug, but the unittest passes normally.)
bors
added a commit
that referenced
this pull request
Apr 30, 2013
`std::bigint` contains the following code. ```rust borrow = *elem << (uint::bits - n_bits); ``` The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand, because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture. If `--opt-level` option is not given to rustc, the code above runs as if the right operand is `(uint::bits - n_bits) % 32`, but if --opt-level is given, `borrow` is always zero. I wonder why this bug is not catched in the libstd's testsuite (I try the `rustc --test --opt-level=2 bigint.rs` before fixing the bug, but the unittest passes normally.) This pull request also removes the implicit vector copies in `bigint.rs`.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
std::bigintcontains the following code.The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand,
because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture.
If
--opt-leveloption is not given to rustc, the code above runs as if the right operand is(uint::bits - n_bits) % 32,but if --opt-level is given,
borrowis always zero.I wonder why this bug is not catched in the libstd's testsuite (I try the
rustc --test --opt-level=2 bigint.rsbefore fixing the bug,but the unittest passes normally.)
This pull request also removes the implicit vector copies in
bigint.rs.