golang.org/x/exp@v0.0.0-20240506185415-9bf2ced13842/shootout/fannkuch.c (about)

     1  // +build ignore
     2  
     3  /*
     4  Redistribution and use in source and binary forms, with or without
     5  modification, are permitted provided that the following conditions are met:
     6  
     7      * Redistributions of source code must retain the above copyright
     8      notice, this list of conditions and the following disclaimer.
     9  
    10      * Redistributions in binary form must reproduce the above copyright
    11      notice, this list of conditions and the following disclaimer in the
    12      documentation and/or other materials provided with the distribution.
    13  
    14      * Neither the name of "The Computer Language Benchmarks Game" nor the
    15      name of "The Computer Language Shootout Benchmarks" nor the names of
    16      its contributors may be used to endorse or promote products derived
    17      from this software without specific prior written permission.
    18  
    19  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    20  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    21  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    22  ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    23  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    24  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    25  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    26  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    27  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    28  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    29  POSSIBILITY OF SUCH DAMAGE.
    30  */
    31  
    32  /*
    33   * The Computer Language Shootout
    34   * http://shootout.alioth.debian.org/
    35   * Contributed by Heiner Marxen
    36   *
    37   * "fannkuch"	for C gcc
    38   *
    39   * $Id: fannkuch.1.gcc.code,v 1.15 2009-04-28 15:39:31 igouy-guest Exp $
    40   */
    41  
    42  #include <stdio.h>
    43  #include <stdlib.h>
    44  
    45  #define Int	int
    46  #define Aint	int
    47  
    48      static long
    49  fannkuch( int n )
    50  {
    51      Aint*	perm;
    52      Aint*	perm1;
    53      Aint*	count;
    54      long	flips;
    55      long	flipsMax;
    56      Int		r;
    57      Int		i;
    58      Int		k;
    59      Int		didpr;
    60      const Int	n1	= n - 1;
    61  
    62      if( n < 1 ) return 0;
    63  
    64      perm  = calloc(n, sizeof(*perm ));
    65      perm1 = calloc(n, sizeof(*perm1));
    66      count = calloc(n, sizeof(*count));
    67  
    68      for( i=0 ; i<n ; ++i ) perm1[i] = i;	/* initial (trivial) permu */
    69  
    70      r = n; didpr = 0; flipsMax = 0;
    71      for(;;) {
    72  	if( didpr < 30 ) {
    73  	    for( i=0 ; i<n ; ++i ) printf("%d", (int)(1+perm1[i]));
    74  	    printf("\n");
    75  	    ++didpr;
    76  	}
    77  	for( ; r!=1 ; --r ) {
    78  	    count[r-1] = r;
    79  	}
    80  
    81  #define XCH(x,y)	{ Aint t_mp; t_mp=(x); (x)=(y); (y)=t_mp; }
    82  
    83  	if( ! (perm1[0]==0 || perm1[n1]==n1) ) {
    84  	    flips = 0;
    85  	    for( i=1 ; i<n ; ++i ) {	/* perm = perm1 */
    86  		perm[i] = perm1[i];
    87  	    }
    88  	    k = perm1[0];		/* cache perm[0] in k */
    89  	    do {			/* k!=0 ==> k>0 */
    90  		Int	j;
    91  		for( i=1, j=k-1 ; i<j ; ++i, --j ) {
    92  		    XCH(perm[i], perm[j])
    93  		}
    94  		++flips;
    95  		/*
    96  		 * Now exchange k (caching perm[0]) and perm[k]... with care!
    97  		 * XCH(k, perm[k]) does NOT work!
    98  		 */
    99  		j=perm[k]; perm[k]=k ; k=j;
   100  	    }while( k );
   101  	    if( flipsMax < flips ) {
   102  		flipsMax = flips;
   103  	    }
   104  	}
   105  
   106  	for(;;) {
   107  	    if( r == n ) {
   108  		return flipsMax;
   109  	    }
   110  	    /* rotate down perm[0..r] by one */
   111  	    {
   112  		Int	perm0 = perm1[0];
   113  		i = 0;
   114  		while( i < r ) {
   115  		    k = i+1;
   116  		    perm1[i] = perm1[k];
   117  		    i = k;
   118  		}
   119  		perm1[r] = perm0;
   120  	    }
   121  	    if( (count[r] -= 1) > 0 ) {
   122  		break;
   123  	    }
   124  	    ++r;
   125  	}
   126      }
   127  }
   128  
   129      int
   130  main( int argc, char* argv[] )
   131  {
   132      int		n = (argc>1) ? atoi(argv[1]) : 0;
   133  
   134      printf("Pfannkuchen(%d) = %ld\n", n, fannkuch(n));
   135      return 0;
   136  }