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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Use a correct and transparent definition of \"code unit\" in C code","articleBody":"We should define `_Py_CODEUNIT` properly without the need for type punning.\r\n\r\nCurrently `_Py_CODEUNIT`  is define as `typedef uint16_t _Py_CODEUNIT;` but it really an 8 bit opcode followed a bit operand aligned to 16 bits. Which means we need to resort to type punning to access the operand and oparg individually.\r\nE.g. https://github.com/python/cpython/blob/main/Include/cpython/code.h#L32\r\n\r\nPEP 7 states that \"Python 3.11 and newer versions use C11 without optional_features\".\r\nSo let's use a union with anonymous struct to define it properly:\r\n\r\n```C\r\ntypedef union {\r\n    int16_t align;\r\n    struct {\r\n         uint8_t opcode;\r\n         uint8_t oparg;\r\n    };\r\n} _Py_CODEUNIT;\r\n```\r\n\r\n@iritkatriel thoughts?\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-100223\n* gh-100259\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/markshannon","@type":"Person","name":"markshannon"},"datePublished":"2022-12-13T14:11:05.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/100222/cpython/issues/100222"}