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| -rw-r--r-- | src/tools/clippy/src/docs/bad_bit_mask.txt | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/src/tools/clippy/src/docs/bad_bit_mask.txt b/src/tools/clippy/src/docs/bad_bit_mask.txt new file mode 100644 index 000000000..d40024ee5 --- /dev/null +++ b/src/tools/clippy/src/docs/bad_bit_mask.txt @@ -0,0 +1,30 @@ +### What it does +Checks for incompatible bit masks in comparisons. + +The formula for detecting if an expression of the type `_ <bit_op> m +<cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of +{`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following +table: + +|Comparison |Bit Op|Example |is always|Formula | +|------------|------|-------------|---------|----------------------| +|`==` or `!=`| `&` |`x & 2 == 3` |`false` |`c & m != c` | +|`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` | +|`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` | +|`==` or `!=`| `\|` |`x \| 1 == 0`|`false` |`c \| m != c` | +|`<` or `>=`| `\|` |`x \| 1 < 1` |`false` |`m >= c` | +|`<=` or `>` | `\|` |`x \| 1 > 0` |`true` |`m > c` | + +### Why is this bad? +If the bits that the comparison cares about are always +set to zero or one by the bit mask, the comparison is constant `true` or +`false` (depending on mask, compared value, and operators). + +So the code is actively misleading, and the only reason someone would write +this intentionally is to win an underhanded Rust contest or create a +test-case for this lint. + +### Example +``` +if (x & 1 == 2) { } +```
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