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118 lines
4.0 KiB
C
118 lines
4.0 KiB
C
/* This program by D E Knuth is in the public domain and freely copyable
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* AS LONG AS YOU MAKE ABSOLUTELY NO CHANGES!
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* It is explained in Seminumerical Algorithms, 3rd edition, Section 3.6
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* (or in the errata to the 2nd edition --- see
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* http://www-cs-faculty.stanford.edu/~knuth/taocp.html
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* in the changes to Volume 2 on pages 171 and following). */
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/* N.B. The MODIFICATIONS introduced in the 9th printing (2002) are
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included here; there's no backwards compatibility with the original. */
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/* This version also adopts Brendan McKay's suggestion to
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accommodate naive users who forget to call ran_start(seed). */
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/* If you find any bugs, please report them immediately to
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* taocp@cs.stanford.edu
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* (and you will be rewarded if the bug is genuine). Thanks! */
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/************ see the book for explanations and caveats! *******************/
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/************ in particular, you need two's complement arithmetic **********/
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#define KK 100 /* the long lag */
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#define LL 37 /* the short lag */
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#define MM (1L<<30) /* the modulus */
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#define mod_diff(x,y) (((x)-(y))&(MM-1)) /* subtraction mod MM */
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long ran_x[KK]; /* the generator state */
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#ifdef __STDC__
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void ran_array(long aa[],int n)
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#else
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void ran_array(aa,n) /* put n new random numbers in aa */
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long *aa; /* destination */
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int n; /* array length (must be at least KK) */
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#endif
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{
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register int i,j;
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for (j=0;j<KK;j++) aa[j]=ran_x[j];
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for (;j<n;j++) aa[j]=mod_diff(aa[j-KK],aa[j-LL]);
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for (i=0;i<LL;i++,j++) ran_x[i]=mod_diff(aa[j-KK],aa[j-LL]);
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for (;i<KK;i++,j++) ran_x[i]=mod_diff(aa[j-KK],ran_x[i-LL]);
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}
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/* the following routines are from exercise 3.6--15 */
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/* after calling ran_start, get new randoms by, e.g., "x=ran_arr_next()" */
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#define QUALITY 1009 /* recommended quality level for high-res use */
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long ran_arr_buf[QUALITY];
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long ran_arr_dummy=-1, ran_arr_started=-1;
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long *ran_arr_ptr=&ran_arr_dummy; /* the next random number, or -1 */
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#define TT 70 /* guaranteed separation between streams */
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#define is_odd(x) ((x)&1) /* units bit of x */
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#ifdef __STDC__
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void ran_start(long seed)
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#else
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void ran_start(seed) /* do this before using ran_array */
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long seed; /* selector for different streams */
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#endif
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{
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register int t,j;
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long x[KK+KK-1]; /* the preparation buffer */
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register long ss=(seed+2)&(MM-2);
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for (j=0;j<KK;j++) {
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x[j]=ss; /* bootstrap the buffer */
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ss<<=1; if (ss>=MM) ss-=MM-2; /* cyclic shift 29 bits */
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}
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x[1]++; /* make x[1] (and only x[1]) odd */
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for (ss=seed&(MM-1),t=TT-1; t; ) {
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for (j=KK-1;j>0;j--) x[j+j]=x[j], x[j+j-1]=0; /* "square" */
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for (j=KK+KK-2;j>=KK;j--)
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x[j-(KK-LL)]=mod_diff(x[j-(KK-LL)],x[j]),
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x[j-KK]=mod_diff(x[j-KK],x[j]);
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if (is_odd(ss)) { /* "multiply by z" */
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for (j=KK;j>0;j--) x[j]=x[j-1];
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x[0]=x[KK]; /* shift the buffer cyclically */
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x[LL]=mod_diff(x[LL],x[KK]);
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}
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if (ss) ss>>=1; else t--;
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}
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for (j=0;j<LL;j++) ran_x[j+KK-LL]=x[j];
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for (;j<KK;j++) ran_x[j-LL]=x[j];
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for (j=0;j<10;j++) ran_array(x,KK+KK-1); /* warm things up */
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ran_arr_ptr=&ran_arr_started;
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}
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#define ran_arr_next() (*ran_arr_ptr>=0? *ran_arr_ptr++: ran_arr_cycle())
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long ran_arr_cycle()
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{
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if (ran_arr_ptr==&ran_arr_dummy)
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ran_start(314159L); /* the user forgot to initialize */
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ran_array(ran_arr_buf,QUALITY);
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ran_arr_buf[KK]=-1;
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ran_arr_ptr=ran_arr_buf+1;
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return ran_arr_buf[0];
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}
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/* Tweaked to include as a library - Fletcher T. Penney */
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/*#include <stdio.h>
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int main()
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{
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register int m; long a[2009];
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ran_start(310952L);
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for (m=0;m<=2009;m++) ran_array(a,1009);
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printf("%ld\n", a[0]); *//* 995235265 */
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/* ran_start(310952L);
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for (m=0;m<=1009;m++) ran_array(a,2009);
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printf("%ld\n", a[0]); *//* 995235265 */
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/* printf("%ld\n",ran_arr_next());
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return 0;
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} */
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long ran_num_next()
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{
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return ran_arr_next();
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}
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