BITSET(9)

✨ NAME ✨

okay so bestie, meet bitset(9) 💖 — it's not one thing, it's a whole squad. This is the bitset manipulation macros family, and yes it's a long list, and yes I'm giving every single one of them their moment:

BITSET_DEFINE, BITSET_T_INITIALIZER, BITSET_FSET, BIT_CLR, BIT_COPY, BIT_ISSET, BIT_SET, BIT_ZERO, BIT_FILL, BIT_SETOF, BIT_EMPTY, BIT_ISFULLSET, BIT_FFS, BIT_FLS, BIT_COUNT, BIT_SUBSET, BIT_OVERLAP, BIT_CMP, BIT_OR, BIT_OR2, BIT_AND, BIT_AND2, BIT_NAND, BIT_NAND2, BIT_XOR, BIT_XOR2, BIT_CLR_ATOMIC, BIT_SET_ATOMIC, BIT_SET_ATOMIC_ACQ, BIT_AND_ATOMIC, BIT_OR_ATOMIC, BIT_COPY_STORE_REL.

That's the roster. Kernel Developer's Manual energy, but make it cute 💅

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🦋 SYNOPSIS 🦋

#include <sys/_bitset.h>
#include <sys/bitset.h>

BITSET_DEFINE(STRUCTNAME, const SETSIZE);

BITSET_T_INITIALIZER(ARRAY_CONTENTS);

BITSET_FSET(N_WORDS);

BIT_CLR(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

BIT_COPY(const SETSIZE, struct STRUCTNAME *from, struct STRUCTNAME *to);

bool
BIT_ISSET(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

BIT_SET(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

BIT_ZERO(const SETSIZE, struct STRUCTNAME *bitset);

BIT_FILL(const SETSIZE, struct STRUCTNAME *bitset);

BIT_SETOF(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

bool
BIT_EMPTY(const SETSIZE, struct STRUCTNAME *bitset);

bool
BIT_ISFULLSET(const SETSIZE, struct STRUCTNAME *bitset);

int
BIT_FFS(const SETSIZE, struct STRUCTNAME *bitset);

int
BIT_FLS(const SETSIZE, struct STRUCTNAME *bitset);

int
BIT_COUNT(const SETSIZE, struct STRUCTNAME *bitset);

bool
BIT_SUBSET(const SETSIZE, struct STRUCTNAME *haystack,
    struct STRUCTNAME *needle);

bool
BIT_OVERLAP(const SETSIZE, struct STRUCTNAME *bitset1,
    struct STRUCTNAME *bitset2);

bool
BIT_CMP(const SETSIZE, struct STRUCTNAME *bitset1,
    struct STRUCTNAME *bitset2);

BIT_OR(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src);

BIT_OR2(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src1,
    struct STRUCTNAME *src2);

BIT_AND(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src);

BIT_AND2(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src1,
    struct STRUCTNAME *src2);

BIT_NAND(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src);

BIT_NAND2(const SETSIZE, struct STRUCTNAME *dst,
    struct STRUCTNAME *src1, struct STRUCTNAME *src2);

BIT_XOR(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src);

BIT_XOR2(const SETSIZE, struct STRUCTNAME *dst, struct STRUCTNAME *src1,
    struct STRUCTNAME *src2);

BIT_CLR_ATOMIC(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

BIT_SET_ATOMIC(const SETSIZE, size_t bit, struct STRUCTNAME *bitset);

BIT_SET_ATOMIC_ACQ(const SETSIZE, size_t bit,
    struct STRUCTNAME *bitset);

BIT_AND_ATOMIC(const SETSIZE, struct STRUCTNAME *dst,
    struct STRUCTNAME *src);

BIT_OR_ATOMIC(const SETSIZE, struct STRUCTNAME *dst,
    struct STRUCTNAME *src);

BIT_COPY_STORE_REL(const SETSIZE, struct STRUCTNAME *from,
    struct STRUCTNAME *to);

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💅 DESCRIPTION 💅

The bitset(9) family of macros hands you a flexible and efficient bitset implementation — but only if the maximum size of the set is known at compilation. That's the deal, that's the vibe check, no cap.

Throughout this whole page, the name SETSIZE means the size of the bitset in bits. Individual bits get referenced with indices zero through SETSIZE - 1. And if you want a real-life example of <sys/bitset.h> out in the wild, look at <sys/cpuset.h> 🦋

• BITSET_DEFINE() — defines a bitset struct STRUCTNAME with room to represent SETSIZE bits.
• BITSET_T_INITIALIZER() — lets you initialize a bitset struct with a compile time literal value.
• BITSET_FSET() — generates a compile time literal, usable by BITSET_T_INITIALIZER(), representing a full bitset (all bits set). For examples of BITSET_T_INITIALIZER() and BITSET_FSET() usage, see the “BITSET_T_INITIALIZER EXAMPLE” section. The N_WORDS parameter to BITSET_FSET() should be:

__bitset_words(SETSIZE)

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• BIT_CLR() — clears bit bit in the bitset pointed to by bitset. BIT_CLR_ATOMIC() is identical, but the bit is cleared atomically.
• BIT_COPY() — copies the contents of the bitset from to the bitset to. BIT_COPY_STORE_REL() is similar, but copies component machine words from from and writes them to to with atomic store with release semantics. (That is, if to is composed of multiple machine words, BIT_COPY_STORE_REL() performs multiple individually atomic operations.) 🫶
• BIT_SET() — sets bit bit in the bitset pointed to by bitset. BIT_SET_ATOMIC() is identical, but the bit is set atomically. BIT_SET_ATOMIC_ACQ() sets the bit with acquire semantics.
• BIT_ZERO() — clears all bits in bitset.
• BIT_FILL() — sets all bits in bitset.
• BIT_SETOF() — clears all bits in bitset before setting only bit bit. It's giving "scorched earth, then one single star" ⭐
• BIT_EMPTY() — returns true if bitset is empty.
• BIT_ISFULLSET() — returns true if bitset is full (all bits set).
• BIT_FFS() — returns the 1-index of the first (lowest) set bit in bitset, or zero if bitset is empty. Like with ffs(3), to use the non-zero result of BIT_FFS() as a bit index parameter to any other bitset(9) macro, you must subtract one from the result. 🙈
• BIT_FLS() — returns the 1-index of the last (highest) set bit in bitset, or zero if bitset is empty. Like with fls(3), to use the non-zero result of BIT_FLS() as a bit index parameter to any other bitset(9) macro, you must subtract one from the result. Same energy, opposite end, iykyk.
• BIT_COUNT() — returns the total number of set bits in bitset.
• BIT_SUBSET() — returns true if needle is a subset of haystack. 🪡
• BIT_OVERLAP() — returns true if bitset1 and bitset2 have any common bits. (That is, if bitset1 AND bitset2 is not the empty set.)
• BIT_CMP() — returns true if bitset1 is NOT equal to bitset2. Not me pointing out the double negative, but yes, true means they're different 💀
• BIT_OR() — sets bits present in src in dst. (It is the bitset(9) equivalent of the scalar: dst |= src.) BIT_OR_ATOMIC() is similar, but sets bits in the component machine words in dst atomically. (That is, if dst is composed of multiple machine words, BIT_OR_ATOMIC() performs multiple individually atomic operations.)
• BIT_OR2() — computes src1 bitwise or src2 and assigns the result to dst. (It is the bitset(9) equivalent of the scalar: dst = src1 | src2.)
• BIT_AND() — clears bits absent from src from dst. (It is the bitset(9) equivalent of the scalar: dst &= src.) BIT_AND_ATOMIC() is similar, with the same atomic semantics as BIT_OR_ATOMIC().
• BIT_AND2() — computes src1 bitwise and src2 and assigns the result to dst. (It is the bitset(9) equivalent of the scalar: dst = src1 & src2.)
• BIT_NAND() — clears bits set in src from dst. (It is the bitset(9) equivalent of the scalar: dst &= ~ src.)
• BIT_NAND2() — computes src1 bitwise and not src2 and assigns the result to dst. (It is the bitset(9) equivalent of the scalar: dst = src1 & ~ src2.)
• BIT_XOR() — toggles bits set in src in dst. (It is the bitset(9) equivalent of the scalar: dst ^= src.) 🔥
• BIT_XOR2() — computes src1 bitwise exclusive or src2 and assigns the result to dst. (It is the bitset(9) equivalent of the scalar: dst = src1 ^ src2.)

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🎀 BITSET_T_INITIALIZER EXAMPLE 🎀

BITSET_DEFINE(_myset, MYSETSIZE);

struct _myset myset;

/* Initialize myset to filled (all bits set) */
myset = BITSET_T_INITIALIZER(BITSET_FSET(__bitset_words(MYSETSIZE)));

/* Initialize myset to only the lowest bit set */
myset = BITSET_T_INITIALIZER(0x1);

Look at that. Two whole moods: all the bits, or exactly one bit. Main character energy either way 👑

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🌈 SEE ALSO 🌈

bitstring(3), cpuset(9)

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👑 HISTORY 👑

The bitset(9) macros first appeared in FreeBSD 10.0 in January 2014. They were MFCed to FreeBSD 9.3, released in July 2014. A glow-up so good it got backported 💖

This manual page first appeared in FreeBSD 11.0.

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🫶 AUTHORS 🫶

The bitset(9) macros were generalized and pulled out of <sys/cpuset.h> as <sys/_bitset.h> and <sys/bitset.h> by Attilio Rao <attilio@FreeBSD.org>. This manual page was written by Conrad Meyer <cem@FreeBSD.org>. Legends, honestly 🌸

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💀 CAVEATS 💀

• The SETSIZE argument to all of these macros must match the value given to BITSET_DEFINE(). Fr fr. Don't mix and match, bestie, that's not a vibe. 😭
• Unlike every other reference to individual set members, which are zero-indexed, BIT_FFS() and BIT_FLS() return a one-indexed result (or zero if the set is empty). Yes this is the trap. Yes I'm telling you twice. Yes you'll still forget. 💅

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Debian, July 7, 2017 — that's the whole source/version + date receipt, and this page is officially done. Byeee, go set some bits 🦋✨