bitstring(3bsd)

✨ bitstring — the bit-string manipulation macros bestie era ✨

okay so this is bitstring(3bsd) from the LOCAL manual, and it's literally just a bunch of macros for messing with strings of bits. tiny bits. baby bits. let's get into it 💅

🫶 NAME

bit_alloc, bit_clear, bit_decl, bit_ffs, bit_nclear, bit_nset, bit_set, bitstr_size, bit_test — bit-string manipulation macros

📚 LIBRARY

Utility functions from BSD systems (libbsd, -lbsd)

🌸 SYNOPSIS

#include <bitstring.h>
(See libbsd(7) for include usage.)

bitstr_t *
bit_alloc(int nbits);

void
bit_decl(bitstr_t *name, int nbits);

void
bit_clear(bitstr_t *name, int bit);

void
bit_ffc(bitstr_t *name, int nbits, int *value);

void
bit_ffs(bitstr_t *name, int nbits, int *value);

void
bit_nclear(bitstr_t *name, int start, int stop);

void
bit_nset(bitstr_t *name, int start, int stop);

void
bit_set(bitstr_t *name, int bit);

int
bitstr_size(int nbits);

int
bit_test(bitstr_t *name, int bit);

also bestie: the include usage deets live in libbsd(7), go peek there if you need them 💖

👑 DESCRIPTION

These macros operate on strings of bits. yes, strings. of bits. it's giving very low-level, very cunty, very efficient ✨

• The macro bit_alloc() returns a pointer of type “bitstr_t *” to sufficient space to store nbits bits, or NULL if no space is available. so if you get NULL, that's your sign, no room at the inn 😭
• The macro bit_decl() allocates sufficient space to store nbits bits on the stack. stack queen behavior 🎀
• The macro bitstr_size() returns the number of elements of type bitstr_t necessary to store nbits bits. This is useful for copying bit strings. lowkey the copy-paste bestie of this whole friend group 🦋
• The macros bit_clear() and bit_set() clear or set the zero-based numbered bit bit, in the bit string name. zero-based, bestie, not one-based, do not come for me 🙈
• The bit_nset() and bit_nclear() macros set or clear the zero-based numbered bits from start through stop in the bit string name. it's a range, it goes from start all the way through stop, inclusive energy 💜
• The bit_test() macro evaluates to non-zero if the zero-based numbered bit bit of bit string name is set, and zero otherwise. so like… is it on or is it off, no in-between ⭐
• The bit_ffs() macro stores in the location referenced by value the zero-based number of the first bit set in the array of nbits bits referenced by name. If no bits are set, the location referenced by value is set to -1. ffs = first first set, iconic abbreviation, ate 🔥
• The macro bit_ffc() stores in the location referenced by value the zero-based number of the first bit not set in the array of nbits bits referenced by name. If all bits are set, the location referenced by value is set to -1. that's first first clear, for the record 💅
• The arguments to these macros are evaluated only once and may safely have side effects. this is the good news bestie, no double-evaluation jumpscare, we're safe 🫶

🌈 EXAMPLES

here's the whole vibe, verbatim, don't touch a character:

#include <limits.h>
#include <bsd/bitstring.h>

...
#define LPR_BUSY_BIT            0
#define LPR_FORMAT_BIT          1
#define LPR_DOWNLOAD_BIT        2
...
#define LPR_AVAILABLE_BIT       9
#define LPR_MAX_BITS            10

make_lpr_available()
{
        bitstr_t bit_decl(bitlist, LPR_MAX_BITS);
        ...
        bit_nclear(bitlist, 0, LPR_MAX_BITS - 1);
        ...
        if (!bit_test(bitlist, LPR_BUSY_BIT)) {
                bit_clear(bitlist, LPR_FORMAT_BIT);
                bit_clear(bitlist, LPR_DOWNLOAD_BIT);
                bit_set(bitlist, LPR_AVAILABLE_BIT);
        }
}

like… the way she declares the bits on the stack, nukes the whole range with bit_nclear, then checks if she's busy before setting herself available?? main character energy fr fr 💖

🔍 SEE ALSO

• malloc(3)

🕰️ HISTORY

The bitstring functions first appeared in 4.4BSD. old money. vintage. still slaying to this day 👑

and that's the whole page bestie!! this one shipped from Debian and it's dated July 19, 1993 — yes, 1993, she's been serving bits since before most of us existed 😭💀 go forth and manipulate those bit strings, i'm obsessed with you, mwah 💋🎀