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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"2.6:The statement that `inc rax` takes 1 byte in x86 is incorrect.","articleBody":"in section 2.6,you noted \"something simple and very common like inc rax takes one byte\".\n\nIn the x86_64 architecture, the machine code for the inc rax instruction is actually \\x48\\xff\\xc0 and inc eax is \\xff\\xc0, which is not 1 byte long. The confusion likely arises from mixing up with the 32-bit version of the instruction.\n\nIn the x86 (32-bit) architecture, the instruction inc eax has the machine code \\x40, which is indeed 1 byte. However, when moving to the x86_64 (64-bit) architecture, the instruction inc rax requires a REX prefix (\\x48), followed by \\xff\\xc0, making the total size 3 bytes.\n\nTo clarify:\n\nIn x86 (32-bit): inc eax machine code is \\x40 (1 byte).\nIn x86_64 (64-bit): inc rax machine code is \\x48\\xff\\xc0 (3 bytes), with the \\x48 prefix indicating the use of the 64-bit register (rax instead of eax).\nThis distinction is important for understanding how machine code differs between 32-bit and 64-bit architectures. Therefore, the statement that \"inc rax takes 1 byte\" should be corrected to reflect that it actually requires 3 bytes in x86_64.","author":{"url":"https://github.com/collectcrop","@type":"Person","name":"collectcrop"},"datePublished":"2025-02-26T13:18:58.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/329/algorithmica/issues/329"}