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Fix invalid 128-bit division on 32-bit target (#41228)#41250

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kennytm:fix-41228
Apr 13, 2017
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Fix invalid 128-bit division on 32-bit target (#41228)#41250
bors merged 1 commit into
rust-lang:masterfrom
kennytm:fix-41228

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@kennytm

@kennytm kennytm commented Apr 12, 2017

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The bug of #41228 is a typo, this line:

rust/src/libcompiler_builtins/lib.rs

Line 183 in 1dca19a

q = n.wrapping_shl(64u32.wrapping_sub(sr)); 

            // 1 <= sr <= u64::bits() - 1
            q = n.wrapping_shl(64u32.wrapping_sub(sr));

The 64 should be 128.

(Compare with https://github.com/rust-lang-nursery/compiler-builtins/blob/280d19f1127aa80739f4179152b11a5f7d36d79f/src/int/udiv.rs#L213-L214:

            // 1 <= sr <= <hty!($ty)>::bits() - 1
            q = n << (<$ty>::bits() - sr);

Or compare with the C implementation https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/udivmodti4.c#L113-L116

        /* 1 <= sr <= n_udword_bits - 1 */
        /* q.all = n.all << (n_utword_bits - sr); */
        q.s.low = 0;
        q.s.high = n.s.low << (n_udword_bits - sr);

)

Added a bunch of randomly generated division test cases to try to cover every described branch of udivmodti4.

@kennytm
Fixed invalid 128-bit division on 32-bit target. Fixed issue rust-lan…
71a9e10 
…g#41228.

Added test cases to cover all special-cased branches of udivmodti4.
@rust-highfive

rust-highfive commented Apr 12, 2017

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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

@est31

est31 commented Apr 12, 2017

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Looks good. Thanks for the quick fix @kennytm!

@nikomatsakis

nikomatsakis commented Apr 12, 2017

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@bors r+

@bors

bors commented Apr 12, 2017

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📌 Commit 71a9e10 has been approved by nikomatsakis

nikomatsakis
nikomatsakis reviewed Apr 12, 2017
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Comment thread src/libcompiler_builtins/lib.rs
@@ -180,7 +180,7 @@ pub mod reimpls {
sr = sr.wrapping_add(1);

// 1 <= sr <= u64::bits() - 1

@nikomatsakis nikomatsakis Apr 12, 2017

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Actually, is the comment still correct?

@est31 est31 Apr 12, 2017

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Yes, its consistent with the comment in the c implementation /* 1 <= sr <= n_udword_bits - 1 */.

Its types are defined here and here.

@est31 est31 Apr 12, 2017

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And the C code is actually assuming it when executing the shift, it sets the low value to 0 because it knows that n gets shifted at least by 65 bits.

@kennytm kennytm Apr 12, 2017

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@nikomatsakis The comment is about the range of sr, not the amount of shift, so it is still correct.

@frewsxcv frewsxcv mentioned this pull request Apr 13, 2017
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@bors

bors commented Apr 13, 2017

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⌛ Testing commit 71a9e10 with merge 9f151fd...

@bors

bors commented Apr 13, 2017

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💔 Test failed - status-appveyor

@TimNN

TimNN commented Apr 13, 2017

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@bors retry

frewsxcv added a commit to frewsxcv/rust that referenced this pull request Apr 13, 2017
@frewsxcv
Rollup merge of rust-lang#41250 - kennytm:fix-41228, r=nikomatsakis
74e9d55 
Fix invalid 128-bit division on 32-bit target (rust-lang#41228)

The bug of rust-lang#41228 is a typo, this line: https://github.com/rust-lang/rust/blob/1dca19ae3fd195fa517e326a39bfee729da7cadb/src/libcompiler_builtins/lib.rs#L183

```rust
            // 1 <= sr <= u64::bits() - 1
            q = n.wrapping_shl(64u32.wrapping_sub(sr));
```

The **64** should be **128**.

(Compare with https://github.com/rust-lang-nursery/compiler-builtins/blob/280d19f1127aa80739f4179152b11a5f7d36d79f/src/int/udiv.rs#L213-L214:

```rust
            // 1 <= sr <= <hty!($ty)>::bits() - 1
            q = n << (<$ty>::bits() - sr);
```

Or compare with the C implementation https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/udivmodti4.c#L113-L116

```c
        /* 1 <= sr <= n_udword_bits - 1 */
        /* q.all = n.all << (n_utword_bits - sr); */
        q.s.low = 0;
        q.s.high = n.s.low << (n_udword_bits - sr);
```
)

Added a bunch of randomly generated division test cases to try to cover every described branch of `udivmodti4`.
@frewsxcv frewsxcv mentioned this pull request Apr 13, 2017
Closed
frewsxcv added a commit to frewsxcv/rust that referenced this pull request Apr 13, 2017
@frewsxcv
Rollup merge of rust-lang#41250 - kennytm:fix-41228, r=nikomatsakis
8fb849d 
Fix invalid 128-bit division on 32-bit target (rust-lang#41228)

The bug of rust-lang#41228 is a typo, this line: https://github.com/rust-lang/rust/blob/1dca19ae3fd195fa517e326a39bfee729da7cadb/src/libcompiler_builtins/lib.rs#L183

```rust
            // 1 <= sr <= u64::bits() - 1
            q = n.wrapping_shl(64u32.wrapping_sub(sr));
```

The **64** should be **128**.

(Compare with https://github.com/rust-lang-nursery/compiler-builtins/blob/280d19f1127aa80739f4179152b11a5f7d36d79f/src/int/udiv.rs#L213-L214:

```rust
            // 1 <= sr <= <hty!($ty)>::bits() - 1
            q = n << (<$ty>::bits() - sr);
```

Or compare with the C implementation https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/udivmodti4.c#L113-L116

```c
        /* 1 <= sr <= n_udword_bits - 1 */
        /* q.all = n.all << (n_utword_bits - sr); */
        q.s.low = 0;
        q.s.high = n.s.low << (n_udword_bits - sr);
```
)

Added a bunch of randomly generated division test cases to try to cover every described branch of `udivmodti4`.
@frewsxcv frewsxcv mentioned this pull request Apr 13, 2017
Closed
frewsxcv added a commit to frewsxcv/rust that referenced this pull request Apr 13, 2017
@frewsxcv
Rollup merge of rust-lang#41250 - kennytm:fix-41228, r=nikomatsakis
6dfd8f6 
Fix invalid 128-bit division on 32-bit target (rust-lang#41228)

The bug of rust-lang#41228 is a typo, this line: https://github.com/rust-lang/rust/blob/1dca19ae3fd195fa517e326a39bfee729da7cadb/src/libcompiler_builtins/lib.rs#L183

```rust
            // 1 <= sr <= u64::bits() - 1
            q = n.wrapping_shl(64u32.wrapping_sub(sr));
```

The **64** should be **128**.

(Compare with https://github.com/rust-lang-nursery/compiler-builtins/blob/280d19f1127aa80739f4179152b11a5f7d36d79f/src/int/udiv.rs#L213-L214:

```rust
            // 1 <= sr <= <hty!($ty)>::bits() - 1
            q = n << (<$ty>::bits() - sr);
```

Or compare with the C implementation https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/udivmodti4.c#L113-L116

```c
        /* 1 <= sr <= n_udword_bits - 1 */
        /* q.all = n.all << (n_utword_bits - sr); */
        q.s.low = 0;
        q.s.high = n.s.low << (n_udword_bits - sr);
```
)

Added a bunch of randomly generated division test cases to try to cover every described branch of `udivmodti4`.
@frewsxcv frewsxcv mentioned this pull request Apr 13, 2017
Merged
bors added a commit that referenced this pull request Apr 13, 2017
@bors
Auto merge of #41277 - frewsxcv:rollup, r=frewsxcv
ea37682 
Rollup of 3 pull requests

- Successful merges: #41240, #41250, #41266
- Failed merges:
@bors bors merged commit 71a9e10 into rust-lang:master Apr 13, 2017
@nikomatsakis nikomatsakis mentioned this pull request Apr 13, 2017
Closed
@kennytm kennytm deleted the fix-41228 branch April 17, 2017 15:37
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@kennytm @rust-highfive @est31 @nikomatsakis @bors @TimNN