/*- * Copyright (c) 1990 The Regents of the University of California. * All rights reserved. * * %sccs.include.redist.c% */ #if defined(LIBC_SCCS) && !defined(lint) static char sccsid[] = "@(#)radixsort.c 5.1 (Berkeley) 10/01/90"; #endif /* LIBC_SCCS and not lint */ #include #include #include #include #include #define NCHARS (UCHAR_MAX + 1) /* * shellsort (diminishing increment sort) from Data Structures and * Algorithms, Aho, Hopcraft and Ullman, 1983 Edition, page 290; * see also Knuth Vol. 3, page 84. The increments are selected from * formula (8), page 95. Roughly O(N^3/2). * * __rspartition is the cutoff point for a further partitioning instead * of a shellsort. If it changes check __rsshell_increments. Both of * these are exported, as the best values are data dependent. Unrolling * this loop has not proven worthwhile. */ #define NPARTITION 40 int __rspartition = NPARTITION; int __rsshell_increments[] = { 4, 1, 0, 0, 0, 0, 0, 0 }; #define SHELLSORT { \ register u_char ch, *s1, *s2; \ register int incr, *incrp; \ for (incrp = __rsshell_increments; incr = *incrp++;) \ for (t1 = incr; t1 < nmemb; ++t1) \ for (t2 = t1 - incr; t2 >= 0;) { \ s1 = p[t2] + indx; \ s2 = p[t2 + incr] + indx; \ while ((ch = tr[*s1++]) == tr[*s2] && ch) \ ++s2; \ if (ch > tr[*s2]) { \ s1 = p[t2]; \ p[t2] = p[t2 + incr]; \ p[t2 + incr] = s1; \ t2 -= incr; \ } else \ break; \ } \ } /* * stack points to context structures. Each structure defines a * scheduled partitioning. Radixsort exits when the stack is empty. * * The stack size is data dependent, and guessing is probably not * worthwhile. The initial stack fits in 1K with four bytes left over * for malloc. The initial size is exported, as the best value is * data, and possibly, system, dependent. */ typedef struct _stack { u_char **bot; int indx, nmemb; } CONTEXT; int __radix_stacksize = (1024 - 4) / sizeof(CONTEXT); #define STACKPUSH { \ if (stackp == estack) { \ t1 = stackp - stack; \ stackp = stack; \ if (!(stack = (CONTEXT *)realloc((char *)stack, \ (__radix_stacksize *= 2) * sizeof(CONTEXT)))) { \ t1 = errno; \ free((char *)l2); \ if (stackp) \ free((char *)stackp); \ errno = t1; \ return(-1); \ } \ stackp = stack + t1; \ estack = stack + __radix_stacksize; \ } \ stackp->bot = p; \ stackp->nmemb = nmemb; \ stackp->indx = indx; \ ++stackp; \ } #define STACKPOP { \ if (stackp == stack) \ break; \ --stackp; \ bot = stackp->bot; \ nmemb = stackp->nmemb; \ indx = stackp->indx; \ } /* * A variant of MSD radix sorting; see Knuth Vol. 3, page 177, and 5.2.5, * Ex. 10 and 12. Also, "Three Partition Refinement Algorithms, Paige and * Tarjan, SIAM J. Comput. Vol. 16, No. 6, December 1987. * * This uses a simple sort as soon as a bucket crosses a cutoff point, rather * than sorting the entire list after partitioning is finished. * * This is pure MSD instead of LSD of some number of MSD, switching to the * simple sort as soon as possible. Takes linear time relative to the number * of bytes in the strings. */ radixsort(l1, nmemb, tab, endbyte) u_char **l1, *tab, endbyte; register int nmemb; { register int i, indx, t1, t2; register u_char **l2, **p, **bot, *tr; CONTEXT *estack, *stack, *stackp; int c[NCHARS + 1]; u_char ltab[NCHARS]; if (nmemb <= 1) return(0); /* * there are two arrays, one provided by the user (l1), and the * temporary one (l2). The data is sorted to the temporary stack, * and then copied back. The speedup of using index to determine * which stack the data is on and simply swapping stacks back and * forth, thus avoiding the copy every iteration, turns out to not * be any faster than the current implementation. */ if (!(l2 = (u_char **)malloc(sizeof(u_char *) * nmemb))) return(-1); /* initialize stack */ stack = stackp = estack = NULL; /* * tr references a table of sort weights; multiple entries may * map to the same weight; EOS char must have the lowest weight. */ if (tab) tr = tab; else { tr = ltab; for (t1 = 0, t2 = endbyte; t1 < t2; ++t1) tr[t1] = t1 + 1; tr[t2] = 0; for (t1 = endbyte + 1; t1 < NCHARS; ++t1) tr[t1] = t1; } /* first sort is entire stack */ bot = l1; indx = 0; for (;;) { /* clear bucket count array */ bzero((char *)c, sizeof(c)); /* * compute number of items that sort to the same bucket * for this index. */ for (p = bot, i = nmemb; i--;) ++c[tr[(*p++)[indx]]]; /* * sum the number of characters into c, dividing the temp * stack into the right number of buckets for this bucket, * this index. C contains the cumulative total of keys * before and included in this bucket, and will later be * used as an index to the bucket. c[NCHARS] contains * the total number of elements, for determining how many * elements the last bucket contains. */ for (i = 1; i <= NCHARS; ++i) c[i] += c[i - 1]; /* * partition the elements into buckets; c decrements * through the bucket, and ends up pointing to the * first element of the bucket. */ for (i = nmemb; i--;) { --p; l2[--c[tr[(*p)[indx]]]] = *p; } /* copy the partitioned elements back to user stack */ bcopy(l2, bot, nmemb * sizeof(u_char *)); ++indx; /* * sort buckets as necessary; don't sort c[0], it's the * EOS character bucket, and nothing can follow EOS. */ for (i = NCHARS - 1; i; i--) { if ((nmemb = c[i + 1] - (t1 = c[i])) < 2) continue; p = bot + t1; if (nmemb > __rspartition) STACKPUSH else SHELLSORT } /* break out when stack is empty */ STACKPOP } free((char *)l2); free((char *)stack); #ifdef STATS (void)fprintf(stderr, "max stack %u.\n", __radix_stacksize); #endif return(0); }