Bitwise operation for state machine Post: 302880859

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Top Forums Programming Bitwise operation for state machine Post 302880859 by Don Cragun on Tuesday 24th of December 2013 05:07:18 AM

12-24-2013

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So you have a variable (e.g. state) that presumably should always have no more than one of the three low order bits set. (Or, maybe you mean it should always have exactly one of the three low order bits set. Your specification is ambiguous as to which of these you mean.)

How will you tell your machine to change state?
Will you call a function to change the state? If so, why is that function not just an assignment to state? Is it that you want to verify that the requested new state has no more than one (or exactly one) of the three low order bits set?

Maybe you want a function that takes two arguments, states to add to state and states to remove from state.

What language are you using? (I could guess C, but it isn't the only language that includes enums.)

What have you tried so far?

Don Cragun

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mbsinit

MBSINIT(3)						     Linux Programmer's Manual							MBSINIT(3)

NAME

       mbsinit - test for initial shift state

SYNOPSIS

       #include <wchar.h>

       int mbsinit(const mbstate_t *ps);

DESCRIPTION

       Character  conversion  between the multibyte representation and the wide character representation uses conversion state, of type mbstate_t.
       Conversion of a string uses a finite-state machine; when it is interrupted after the complete conversion of a number of characters, it  may
       need to save a state for processing the remaining characters.  Such a conversion state is needed for the sake of encodings such as ISO-2022
       and UTF-7.

       The initial state is the state at the beginning of conversion of a string.  There are two kinds of state: The one used by multibyte to wide
       character  conversion  functions, such as mbsrtowcs(3), and the one used by wide character to multibyte conversion functions, such as wcsr-
       tombs(3), but they both fit in a mbstate_t, and they both have the same representation for an initial state.

       For 8-bit encodings, all states are equivalent to the initial state.  For multibyte encodings like UTF-8, EUC-*, BIG5  or  SJIS,  the  wide
       character to multibyte conversion functions never produce non-initial states, but the multibyte to wide-character conversion functions like
       mbrtowc(3) do produce non-initial states when interrupted in the middle of a character.

       One possible way to create an mbstate_t in initial state is to set it to zero:

	   mbstate_t state;
	   memset(&state,0,sizeof(mbstate_t));

       On Linux, the following works as well, but might generate compiler warnings:

	   mbstate_t state = { 0 };

       The function mbsinit() tests whether *ps corresponds to an initial state.

RETURN VALUE

       mbsinit() returns nonzero if *ps is an initial state, or if ps is a NULL pointer.  Otherwise it returns 0.

CONFORMING TO

       C99.

NOTES

       The behavior of mbsinit() depends on the LC_CTYPE category of the current locale.

SEE ALSO

       mbsrtowcs(3), wcsrtombs(3)

COLOPHON

       This page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2000-11-20								MBSINIT(3)