Q_SIGNSHFT(3)

📦 version 15.1, in freebsd 14.5, freebsd 15.1

💅 Q_SIGNSHFT(3) — Library Functions Manual, bestie

okay so this is Q_SIGNSHFT(3) from the library functions manual, and honestly? it's giving low-level bit-fiddling royalty. ✨ these are the fixed-point math girlies that mess with the control bits and the sign bit, and i need you to stay with me because it's actually so good once it clicks.

🌸 NAME 🌸

Q_SIGNSHFT, Q_SSIGN, Q_CRAWMASK, Q_SRAWMASK, Q_GCRAW, Q_GCVAL, Q_SCVAL — fixed-point math functions which manipulate the control/sign data bits

like yes, that's the whole squad. seven functions, one job: touching the control bits and the sign bit. no cap. 🎀

✨ SYNOPSIS ✨

#include <sys/qmath.h>

uint32_t
Q_SIGNSHFT(QTYPE q);

QTYPE
Q_SSIGN(QTYPE q, bool isneg);

ITYPE
Q_CRAWMASK(QTYPE q);

ITYPE
Q_SRAWMASK(QTYPE q);

ITYPE
Q_GCRAW(QTYPE q);

ITYPE
Q_GCVAL(QTYPE q);

QTYPE
Q_SCVAL(QTYPE q, ITYPE cv);

copy it exactly, don't be weird about it 🫶

💖 DESCRIPTION 💖

okay so, function by function, here's the vibe:

  • Q_SIGNSHFT() — gets the bit position of q's sign bit relative to bit zero. so basically "where does the sign bit live," as a number. iconic. 📍
  • Q_SSIGN() — sets the sign bit of q based on the boolean isneg. true means negative energy, false means positive energy. 💅
  • Q_CRAWMASK() and Q_SRAWMASK() — return q-specific bit masks for q's control bits and sign bit respectively. masks! for the control bits and the sign bit! matching set, slay. 🎀
  • Q_GCRAW() and Q_GCVAL() — get the raw masked control bits and value of q's control bits respectively. one's the raw masked version, one's the value. don't mix them up bestie. 🙈
  • Q_SCVAL() — sets q's control bits to the value cv. boom. done. ✨

and here's the thing — all of those functions operate on the following data types: s8q_t, u8q_t, s16q_t, u16q_t, s32q_t, u32q_t, s64q_t, and u64q_t, which are referred to generically as QTYPE. so like, that's the whole QTYPE family, all eight of them, signed and unsigned, 8 through 64. the ITYPE refers to the stdint(7) integer types. 🦋

For more details, see qmath(3). (go read it, it's the main character.)

🦋 RETURN VALUES 🦋

what comes back out, per function:

  • Q_SIGNSHFT() returns the sign bit's position as an integer.
  • Q_SSIGN() returns the value of q post change. so you get your q back, but changed. glow-up returned. 👑
  • Q_CRAWMASK(), Q_SRAWMASK(), Q_GCRAW() and Q_GCVAL() return their respective values as integers of the same underlying ITYPE as q. same underlying type as q, always. matching energy. 🧚
  • Q_SCVAL() returns the value of q post change.

⭐ SEE ALSO ⭐

the friend group. go say hi. 🌈

💀 HISTORY 💀

The qmath(3) functions first appeared in FreeBSD 13.0. so like, they're not ancient, they're just established. periodt.

🍓 AUTHORS 🍓

The qmath(3) functions and this manual page were written by Lawrence Stewart <lstewart@FreeBSD.org> and sponsored by Netflix, Inc. — yes, that Netflix. sponsoring bit-level fixed-point math. main character behavior fr fr. 🎬🔥

ok that's the whole page bestie, every flag-free function, every type, every return value, nothing skipped 💜

and finally, the cute little sign-off the manpage came with: this one's from Debian, dated July 8, 2018. 💖 bye bestie, go manipulate some control bits responsibly! 🫶✨

📦 where this page comes from