calculate_box_addr(9)

📦 version 7.3.1, in nixpkgs unstable

💅 calculate_box_addr(9) 💅

okay so bestie, welcome to a page straight out of the Kernel API Manual, section 9, and it's literally all about figuring out where a byte actually lives inside a buffer. no cap. 🫶

✨ NAME ✨

calculate_box_addr — determine the physical location of a byte in a buffer 💖

🌸 SYNOPSIS 🌸

size_t calculate_box_addr (size_t box , size_t len , u8 quirks );

like, that's the whole vibe. three args, one size_t coming back at you. 🎀

🦋 ARGUMENTS 🦋

  • box — the index of the byte inside the buffer, except we're seeing the buffer as one big logical big-endian big number. so box is the logical octet number, not the physical one. iykyk. 🔥
  • len — the size of the buffer, in bytes. yes bestie, bytes. 📏
  • quirks — a mask made of QUIRK_LSW32_IS_FIRST and QUIRK_LITTLE_ENDIAN. these two little flags are the main characters of this whole function, ngl. 👑

💜 DESCRIPTION 💜

so the function treats the buffer as a len-byte-sized big number and returns the physical offset of the box logical octet inside it. literally its whole job. ✨

internally, it treats that big number as groups of 4 bytes. if len is not a multiple of 4, the last group may be shorter. that's just how it is, no drama. 🎀

QUIRK_LSW32_IS_FIRST gives you the ordering of those groups of 4 octets relative to each other. if it's set, the most significant group of 4 octets is last in the buffer — and it may be truncated if len is not a multiple of 4. so the big group is serving last-place energy, and we respect it. 💅

QUIRK_LITTLE_ENDIAN gives you the ordering of bytes within each group of 4. if it's set, the most significant byte is last in the group. and if len takes the form of 4k+3, the last group will only be able to represent 24 bits, and its most significant octet is byte 2. okay so that's a whole situation, but it's exactly what the page says, so we're not gonna pretend otherwise. 🫶

lowkey important: those two quirks change where the bytes land, so if you set them wrong you're gonna have a bad time. the page isn't joking around about the truncation either. 💀

🍓 RETURN 🍓

the physical offset into the buffer corresponding to the logical box. that's it. that's the return value. slay. 🔥

🌈 SEE ALSO 🌈

like, go read those too if you want the full packing lore. the friend group is iconic. 👑💖

and that's the page bestie!! this little gem lives in ./lib and it's dated October 2026 — so yeah, mark your calendar, the packing girlies stay booked and busy. 🧚‍♀️🎀💜

📦 where this page comes from