Updated: 2021/Apr/14

BITS(3) Library Functions Manual BITS(3)NAME__BIT, __BITS, __SHIFTIN, __SHIFTOUT, __SHIFTOUT_MASK- macros for preparing bitmasks and operating on bit fieldsSYNOPSIS#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);DESCRIPTIONThese 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).EXAMPLESThe following example demonstrates basic usage of thebitsmacros: 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 */SEEALSObitops(3), cdefs(3)HISTORYThebitsmacros first appeared in atw(4), with different names and implementation. In their current form these macros appeared in NetBSD 4.0.AUTHORSThebitsmacros were written by David Young <dyoung@NetBSD.org>. Matt Thomas <matt@NetBSD.org> suggested important improvements to the implementation, and contributed the macro namesSHIFTIN() andSHIFTOUT(). NetBSD 9.99 November 6, 2016 NetBSD 9.99