Q_QADDI(3)

💅 Q_QADDI(3) — bestie's guide to the qmath integer-math squad 🎀

ok so real talk: this is from the Library Functions Manual, and it's about the fixed-point math functions that apply plain integers to a Q number. yes, plural, there's a whole little friend group of them and we're meeting all six. sit down, hydrate, let's go ✨

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🌸 NAME 🌸

Q_QADDI, Q_QDIVI, Q_QMULI, Q_QSUBI, Q_QFRACI, Q_QCPYVALI — the fixed-point math functions which apply integers to a Q number. that's the whole vibe. six functions, one mission, zero cap 💖

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✨ SYNOPSIS ✨

ok here's the lineup, and yes you include the header first, always:

#include <sys/qmath.h>

int
Q_QADDI(QTYPE *a, ITYPE b);

int
Q_QDIVI(QTYPE *a, ITYPE b);

int
Q_QMULI(QTYPE *a, ITYPE b);

int
Q_QSUBI(QTYPE *a, ITYPE b);

int
Q_QFRACI(QTYPE *q, ITYPE n, ITYPE d);

int
Q_QCPYVALI(QTYPE *q, ITYPE i);

every single one of them returns an int, and the args are exactly as shown — QTYPE pointer first, ITYPE after. don't go rearranging them, they're not that kind of function 🫶

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🦋 DESCRIPTION 🦋

ok so the first four are the classic arithmetic girlies. Q_QADDI(), Q_QDIVI(), Q_QMULI() and Q_QSUBI() will add, divide, multiply or subtract b to/by/from a respectively — and the result gets stored right back in a. in place. main character energy, it's all about a 💅

(quick read of that: Q_QADDI() does a + b, Q_QDIVI() does a / b, Q_QMULI() does a * b, Q_QSUBI() does a - b. all landing back in a. iconic.)

then there's Q_QFRACI(), our fraction specialist 🍓 — it computes the fraction n divided by d and stores the fixed-point result in q. so like, numerator over denominator, but the answer's fixed-point and it lives in q. periodt.

and finally Q_QCPYVALI(), the glow-up function 🌈 — it overwrites q's integer and fractional bits with the Q representation of the integer value i. both sets of bits. gone, replaced, reborn. not me being dramatic about a copy operation 😭

now, the types. all of those functions operate on the following data types, and honestly this is the part you screenshot for later:

• s8q_t
• u8q_t
• s16q_t
• u16q_t
• s32q_t
• u32q_t
• s64q_t
• u64q_t

which are all referred to generically as QTYPE. and the ITYPE? that one refers to the stdint(7) integer types. yes there's a whole other manpage for those, iykyk.

for more details (and there ARE more details, bestie), go see qmath(3). 🧚

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🔥 RETURN VALUES 🔥

ok the vibe check on what comes back:

• Q_QADDI(), Q_QDIVI(), Q_QMULI(), Q_QSUBI(), Q_QFRACI() and Q_QCPYVALI() all return 0 on success ✨
• or an errno on failure. yeah. not vibes.
• EINVAL gets returned for divide-by-zero — like, obviously, you cannot do that, and the function WILL call you out 💀
• EOVERFLOW comes back for overflow
• ERANGE comes back for underflow

so 0 = slay, everything else = read the errno and figure out your life 🙈

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👑 SEE ALSO 👑

go touch these for more lore:

• errno(2)
• qmath(3)
• stdint(7)

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⭐ HISTORY ⭐

the qmath(3) functions first appeared in FreeBSD 13.0. a whole era. we stan a documented origin story 💜

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🎀 AUTHORS 🎀

the qmath(3) functions and this manual page were written by Lawrence Stewart <lstewart@FreeBSD.org> and sponsored by Netflix, Inc. — so yes, your fixed-point math is brought to you by the same people who brought you the "are you still watching?" jump scare 😭 sponsorship slays though, fr fr 🫶

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and that's the page! this lil drop was from the Debian edition, dated July 8, 2018 — shoutout to the footer, we remembered you 💖✨ no cap, now go do some fixed-point math responsibly. 🌸🦋💅