| Issue |
90009
|
| Summary |
Possible bug in compiler-rt 128x128 `wideMultiply`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
tgross35
|
[This bit of code](https://github.com/llvm/llvm-project/blob/49b209d0d1833a339e66735e1288c1805224603e/compiler-rt/lib/builtins/fp_lib.h#L145-L185) seems to have a bug where it is missing the carry bit. This was discovered when I was porting the function to Rust's compiler-rt and results of unit tests disagreed with Python, see https://github.com/rust-lang/compiler-builtins/pull/587#issuecomment-2060543566 and the followup discussion.
To reproduce - `"0xffffffffffffffffffffffffffffffff * 0xffffffffffffffffffffffffffffffff` should be `0xfffffffffffffffffffffffffffffffe00000000000000000000000000000001`, but this function returns `0xfffffffffffffffffffffffffffffffd00000000000000000000000000000001`.
cc @marthadev who found a fix for the Rust side.
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