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libstd: modify wrong shift width #6108

Merged
merged 2 commits into from
Apr 30, 2013
Merged

libstd: modify wrong shift width #6108

merged 2 commits into from
Apr 30, 2013

Commits on Apr 29, 2013

  1. libstd: remove implicit copying of BigInt/BigUint

    @gifnksm
    gifnksm committed Apr 29, 2013
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  2. libstd: modify wrong shift width. 

    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.)
    @gifnksm
    gifnksm committed Apr 29, 2013
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