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Fix incorrect pseudocode for #[repr(C)] struct alignment #766
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| Original file line number | Diff line number | Diff line change | 
|---|---|---|
|  | @@ -197,6 +197,17 @@ Here is this algorithm described in pseudocode. | |
|  | ||
| <!-- ignore: pseudocode --> | ||
| ```rust,ignore | ||
| fn padding_needed_for(offset: usize, alignment: usize) -> usize { | ||
| let misalignment = offset % alignment; | ||
| if misalignment > 0 { | ||
| // round up to next multiple of `alignment` | ||
| alignment - misalignment | ||
| } else { | ||
| // already a multiple of `alignment` | ||
| 0 | ||
| } | ||
| } | ||
|  | ||
| struct.alignment = struct.fields().map(|field| field.alignment).max(); | ||
|  | ||
| let current_offset = 0; | ||
|  | @@ -205,14 +216,14 @@ for field in struct.fields_in_declaration_order() { | |
| // Increase the current offset so that it's a multiple of the alignment | ||
| // of this field. For the first field, this will always be zero. | ||
| // The skipped bytes are called padding bytes. | ||
| current_offset += field.alignment % current_offset; | ||
| current_offset += padding_needed_for(current_offset, field.alignment); | ||
|  | ||
| struct[field].offset = current_offset; | ||
|  | ||
| current_offset += field.size; | ||
| } | ||
|  | ||
| struct.size = current_offset + current_offset % struct.alignment; | ||
| struct.size = current_offset + padding_needed_for(current_offset, struct.alignment); | ||
| There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. @rkanati you didn't touch this one in your PR... do you remember why? Was that an oversight, or was the original code actually correct for some reason? There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. As far as I can tell, that was just an oversight. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I think so, too. It would just have been good to get explicit confirmation. | ||
| ``` | ||
|  | ||
| > Note: This algorithm can produce zero-sized structs. This differs from | ||
|  | ||
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