__rcsid(3) [netbsd man page]

CDEFS(3)						   BSD Library Functions Manual 						  CDEFS(3)

NAME

     cdefs -- common definitions and macros

SYNOPSIS

     #include <sys/cdefs.h>

DESCRIPTION

     The <sys/cdefs.h> header includes some common definitions and macros typical to the C language conventions of NetBSD.  Among these are:

	   o   Certain C language properties and definitions that are versioned according to the support in compilers.	Examples include the
	       __func__ keyword and the restrict type qualifier from C99.

	   o   Macros and definitions specific to compilers, preprocessors, and linkers; see __CONCAT(3), __UNCONST(3), __insn_barrier(3), and
	       attribute(3).

	   o   Utility macros provided for convenience; see __arraycount(3) and bits(3).

     The header also contains the __RCSID() and __KERNEL_RCSID() macros used for version control system (VCS) identifiers.  Thus, all NetBSD
     source code files typically include <sys/cdefs.h>, included as the first thing right after any possible copyright texts;

	   /*-
	    * Copyright (c) 1984 John Doe
	    * All rights reserved.
	    *
	    * Redistribution and use in source and binary forms,
	    * with or without modification, are permitted.
	    */

	   #include <sys/cdefs.h>
	   __RCSID("$NetBSD: cdefs.3,v 1.3 2011/04/08 07:55:04 jruoho Exp $");

     It is possible to identify the RCS keyword strings by using ident(1).

SEE ALSO

     ident(1), param(3), stddef(3), types(3), c(7)

HISTORY

     The <sys/cdefs.h> header was originally imported from 386BSD.

BSD
								   April 8, 2011							       BSD

BITS(3) 						   BSD Library Functions Manual 						   BITS(3)

NAME

     __BIT, __BITS, __SHIFTIN, __SHIFTOUT, __SHIFTOUT_MASK -- macros for preparing bitmasks and operating on bit fields

SYNOPSIS

     #include <sys/param.h>
     #include <sys/cdefs.h>

     uintmax_t
     __BIT(n);

     uintmax_t
     __BITS(m, n);

     __SHIFTIN(v, mask);

     __SHIFTOUT(v, mask);

     __SHIFTOUT_MASK(mask);

DESCRIPTION

     These macros prepare bitmasks, extract bitfields from words, and insert bitfields into words.  A ``bitfield'' is a span of consecutive bits
     defined by a bitmask, where 1s select the bits in the bitfield.

     Use __BIT() and __BITS() to define bitmasks:

	   __BIT(n)
		   Return a bitmask with bit n set, where the least significant bit is bit 0.

	   __BITS(m, n)
		   Return a bitmask with bits m through n, inclusive, set.  It does not matter whether m > n or m <= n.  The least significant bit
		   is bit 0.

     __SHIFTIN(), __SHIFTOUT(), and __SHIFTOUT_MASK() help read and write bitfields from words:

	   __SHIFTIN(v, mask)
			    Left-shift bits v into the bitfield defined by mask, and return them.  No side-effects.

	   __SHIFTOUT(v, mask)
			    Extract and return the bitfield selected by mask from v, right-shifting the bits so that the rightmost selected bit is
			    at bit 0.  No side-effects.

	   __SHIFTOUT_MASK(mask)
			    Right-shift the bits in mask so that the rightmost non-zero bit is at bit 0.  This is useful for finding the greatest
			    unsigned value that a bitfield can hold.  No side-effects.	Note that __SHIFTOUT_MASK(m) = __SHIFTOUT(m, m).

EXAMPLES

     The following example demonstrates basic usage of the bits macros:

	   uint32_t bits, mask, val;

	   bits = __BITS(2, 3); 		   /* 00001100 */
	   mask = __BIT(2) | __BIT(3);		   /* 00001100 */

	   val = __SHIFTIN(0x03, mask); 	   /* 00001100 */
	   val = __SHIFTOUT(0xf, mask); 	   /* 00000011 */

SEE ALSO

     bitops(3), cdefs(3)

HISTORY

     The bits macros first appeared in atw(4), with different names and implementation.  In their current form these macros appeared in
     NetBSD 4.0.

AUTHORS

     The bits macros were written by David Young <dyoung@NetBSD.org>.
     Matt Thomas <matt@NetBSD.org> suggested important improvements to the implementation, and contributed the macro names SHIFTIN() and
     SHIFTOUT().

BUGS

     __BIT() and __BITS() can only express 32-bit bitmasks.

BSD
								 October 17, 2012							       BSD