bit_ffs (3)

Leading comments

 Copyright (c) 1989, 1991, 1993
	The Regents of the University of California.  All rights reserved.

 This code is derived from software contributed to Berkeley by
 Paul Vixie.
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must r...

(The comments found at the beginning of the groff file "man3/bit_ffs.3bsd".)

NAME

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

SYNOPSIS

In bitstring.h (See libbsd(7) for include usage.) Ft bitstr_t * Fn bit_alloc int nbits Ft void Fn bit_decl bitstr_t *name int nbits Ft void Fn bit_clear bitstr_t *name int bit Ft void Fn bit_ffc bitstr_t *name int nbits int *value Ft void Fn bit_ffs bitstr_t *name int nbits int *value Ft void Fn bit_nclear bitstr_t *name int start int stop Ft void Fn bit_nset bitstr_t *name int start int stop Ft void Fn bit_set bitstr_t *name int bit Ft int Fn bitstr_size int nbits Ft int Fn bit_test bitstr_t *name int bit

DESCRIPTION

These macros operate on strings of bits.

The macro Fn bit_alloc returns a pointer of type ``Fa bitstr_t * '' to sufficient space to store Fa nbits bits, or NULL if no space is available.

The macro Fn bit_decl allocates sufficient space to store Fa nbits bits on the stack.

The macro Fn bitstr_size returns the number of elements of type Fa bitstr_t necessary to store Fa nbits bits. This is useful for copying bit strings.

The macros Fn bit_clear and Fn bit_set clear or set the zero-based numbered bit Fa bit , in the bit string name

The Fn bit_nset and Fn bit_nclear macros set or clear the zero-based numbered bits from Fa start through Fa stop in the bit string name

The Fn bit_test macro evaluates to non-zero if the zero-based numbered bit Fa bit of bit string Fa name is set, and zero otherwise.

The Fn bit_ffs macro stores in the location referenced by Fa value the zero-based number of the first bit set in the array of Fa nbits bits referenced by Fa name . If no bits are set, the location referenced by Fa value is set to -1.

The macro Fn bit_ffc stores in the location referenced by Fa value the zero-based number of the first bit not set in the array of Fa nbits bits referenced by Fa name . If all bits are set, the location referenced by Fa value is set to -1.

The arguments to these macros are evaluated only once and may safely have side effects.

EXAMPLES

#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);
        }
}

SEE ALSO

malloc(3)

HISTORY

The bitstring functions first appeared in BSD 4.4