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/*
* jump - trivial prime jump table
*
* Copyright (C) 1999 Landon Curt Noll
*
* Calc is open software; you can redistribute it and/or modify it under
* the terms of the version 2.1 of the GNU Lesser General Public License
* as published by the Free Software Foundation.
*
* Calc is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
* Public License for more details.
*
* A copy of version 2.1 of the GNU Lesser General Public License is
* distributed with calc under the filename COPYING-LGPL. You should have
* received a copy with calc; if not, write to Free Software Foundation, Inc.
* 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
*
* @(#) $Revision: 29.4 $
* @(#) $Id: jump.h,v 29.4 2001/06/08 21:00:58 chongo Exp $
* @(#) $Source: /usr/local/src/cmd/calc/RCS/jump.h,v $
*
* Under source code control: 1994/06/29 04:03:55
* File existed as early as: 1994
*
* chongo <was here> /\oo/\ http://www.isthe.com/chongo/
* Share and enjoy! :-) http://www.isthe.com/chongo/tech/comp/calc/
*/
/*
* If x is divisible by a trivial prime (2,3,5,7,11), then:
*
* x + jmpindx[ (x>>1)%JMPMOD ]
*
* is the value of the smallest value > x that is not divisible by a
* trivial prime. JMPMOD is the product of the odd trivial primes.
*
* This table is useful for skipping values that are obviously not prime
* by skipping values that are a multiple of trivial prime.
*
* If x is not divisible by a trivial prime, then:
*
* x + jmp[ -jmpindx[(x>>1)%JMPMOD] ]
*
* is the value of the smallest value > x that is not divisible by a
* trivial prime.
*
* If jmpindx[y] > 0 (y = x mod JMPMOD*2), then it refers to an 'x' that
* is divisible by a trivial prime and jmpindx[y] is the offset to the next
* value that is not divisible.
*
* If jmpindx[y] <= 0, then 'x' is not divisible by a trivial prime and
* the negative of jmpindx[y] is the index into the jmp[] table. We use
* successive values from jmp[] (wrapping around to the beginning when
* we move off the end of jmp[]) to move to higher and higher values
* that are not divisible by trivial primes.
*
* Instead of testing successive odd values, this system allows us to
* skip odd values divisible by trivial primes. This is process on the
* average reduces the values we need to test by a factor of at least 2.4.
*/
#if !defined(__JUMP_H__)
#define __JUMP_H__
#if defined(CALC_SRC) /* if we are building from the calc source tree */
# include "have_const.h"
#else
# include <calc/have_const.h>
#endif
/*
* trivial prime CONSTants
*/
#define JMPMOD (3*5*7*11) /* product of odd trivial primes */
#define JMPSIZE (2*4*6*10) /* ints mod JMPMOD not div by trivial primes */
#define JPRIME (prime+4) /* pointer to first non-trivial prime */
/* given x, return the index within jmpindx that applies */
#define jmpmod(x) (((x)>>1)%JMPMOD)
/* jmpindx table value */
#define jmpindxval(x) (jmpindx[jmpmod(x)])
/* return the smallest value >= x not divisible by a trivial prime */
#define firstjmp(x,tmp) ((tmp) = jmpindxval(x), ((tmp) > 0) ? ((x)+(tmp)) : (x))
/* given x not divisible by a trivial prime, return jmp[] index */
#define jmpptr(x) (-jmpindxval(x))
/* given a jmp pointer, return current jump increment and bump the pointer */
#define nxtjmp(p) ( *( ((p)<lastjmp) ? ((p)++) : (((p)=jmp),lastjmp) ) )
/* given a jmp pointer, return dec pointer and return previous jump increment */
#define prevjmp(p) ( *( ((p)>jmp) ? (--(p)) : ((p)=lastjmp) ) )
/*
* external jump tables
*/
extern CONST short jmpindx[];
extern CONST unsigned char jmp[];
extern CONST unsigned char *CONST lastjmp;
#endif /* !__JUMP_H__ */
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