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Diffstat (limited to 'reference/C/CONTRIB/SNIP/rg_qsort.c1')
| -rwxr-xr-x | reference/C/CONTRIB/SNIP/rg_qsort.c1 | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/rg_qsort.c1 b/reference/C/CONTRIB/SNIP/rg_qsort.c1 new file mode 100755 index 0000000..d770517 --- /dev/null +++ b/reference/C/CONTRIB/SNIP/rg_qsort.c1 @@ -0,0 +1,150 @@ +/******************************************************************/
+/* qsort.c -- Non-Recursive ANSI Quicksort function */
+/* */
+/* Public domain by Raymond Gardner, Englewood CO February 1991 */
+/* */
+/* Usage: */
+/* qsort(base, nbr_elements, width_bytes, compare_function); */
+/* void *base; */
+/* size_t nbr_elements, width_bytes; */
+/* int (*compare_function)(const void *, const void *); */
+/* */
+/* Sorts an array starting at base, of length nbr_elements, each */
+/* element of size width_bytes, ordered via compare_function, */
+/* which is called as (*compare_function)(ptr_to_element1, */
+/* ptr_to_element2) and returns < 0 if element1 < element2, */
+/* 0 if element1 = element2, > 0 if element1 > element2. */
+/* Most refinements are due to R. Sedgewick. See "Implementing */
+/* Quicksort Programs", Comm. ACM, Oct. 1978, and Corrigendum, */
+/* Comm. ACM, June 1979. */
+/******************************************************************/
+
+#include <stddef.h> /* for size_t definition */
+
+/* prototypes */
+void qsort(void *, size_t, size_t,
+ int (*)(const void *, const void *));
+void swap_chars(char *, char *, size_t);
+
+/*
+** Compile with -DSWAP_INTS if your machine can access an int at an
+** arbitrary location with reasonable efficiency. (Some machines
+** cannot access an int at an odd address at all, so be careful.)
+*/
+
+#ifdef SWAP_INTS
+ void swap_ints(char *, char *, size_t);
+ #define SWAP(a, b) (swap_func((char *)(a), (char *)(b), width))
+#else
+ #define SWAP(a, b) (swap_chars((char *)(a), (char *)(b), size))
+#endif
+
+#define COMP(a, b) ((*comp)((void *)(a), (void *)(b)))
+
+#define T 7 /* subfiles of T or fewer elements will */
+ /* be sorted by a simple insertion sort */
+ /* Note! T must be at least 3 */
+
+void qsort(void *basep, size_t nelems, size_t size,
+ int (*comp)(const void *, const void *))
+{
+ char *stack[40], **sp; /* stack and stack pointer */
+ char *i, *j, *limit; /* scan and limit pointers */
+ size_t thresh; /* size of T elements in bytes */
+ char *base; /* base pointer as char * */
+
+#ifdef SWAP_INTS
+ size_t width; /* width of array element */
+ void (*swap_func)(char *, char *, size_t); /* swap func pointer*/
+
+ width = size; /* save size for swap routine */
+ swap_func = swap_chars; /* choose swap function */
+ if ( size % sizeof(int) == 0 ) { /* size is multiple of ints */
+ width /= sizeof(int); /* set width in ints */
+ swap_func = swap_ints; /* use int swap function */
+ }
+#endif
+
+ base = (char *)basep; /* set up char * base pointer */
+ thresh = T * size; /* init threshold */
+ sp = stack; /* init stack pointer */
+ limit = base + nelems * size;/* pointer past end of array */
+ for ( ;; ) { /* repeat until break... */
+ if ( limit - base > thresh ) { /* if more than T elements */
+ /* swap base with middle */
+ SWAP((((limit-base)/size)/2)*size+base, base);
+ i = base + size; /* i scans left to right */
+ j = limit - size; /* j scans right to left */
+ if ( COMP(i, j) > 0 ) /* Sedgewick's */
+ SWAP(i, j); /* three-element sort */
+ if ( COMP(base, j) > 0 ) /* sets things up */
+ SWAP(base, j); /* so that */
+ if ( COMP(i, base) > 0 ) /* *i <= *base <= *j */
+ SWAP(i, base); /* *base is pivot element */
+ for ( ;; ) { /* loop until break */
+ do /* move i right */
+ i += size; /* until *i >= pivot */
+ while ( COMP(i, base) < 0 );
+ do /* move j left */
+ j -= size; /* until *j <= pivot */
+ while ( COMP(j, base) > 0 );
+ if ( i > j ) /* if pointers crossed */
+ break; /* break loop */
+ SWAP(i, j); /* else swap elements, keep scanning*/
+ }
+ SWAP(base, j); /* move pivot into correct place */
+ if ( j - base > limit - i ) { /* if left subfile larger */
+ sp[0] = base; /* stack left subfile base */
+ sp[1] = j; /* and limit */
+ base = i; /* sort the right subfile */
+ } else { /* else right subfile larger*/
+ sp[0] = i; /* stack right subfile base */
+ sp[1] = limit; /* and limit */
+ limit = j; /* sort the left subfile */
+ }
+ sp += 2; /* increment stack pointer */
+ } else { /* else subfile is small, use insertion sort */
+ for ( j = base, i = j+size; i < limit; j = i, i += size )
+ for ( ; COMP(j, j+size) > 0; j -= size ) {
+ SWAP(j, j+size);
+ if ( j == base )
+ break;
+ }
+ if ( sp != stack ) { /* if any entries on stack */
+ sp -= 2; /* pop the base and limit */
+ base = sp[0];
+ limit = sp[1];
+ } else /* else stack empty, done */
+ break;
+ }
+ }
+}
+
+/*
+** swap nbytes between a and b
+*/
+
+static void swap_chars(char *a, char *b, size_t nbytes)
+{
+ char tmp;
+ do {
+ tmp = *a; *a++ = *b; *b++ = tmp;
+ } while ( --nbytes );
+}
+
+#ifdef SWAP_INTS
+
+/*
+** swap nints between a and b
+*/
+
+static void swap_ints(char *ap, char *bp, size_t nints)
+{
+ int *a = (int *)ap, *b = (int *)bp;
+ int tmp;
+ do {
+ tmp = *a; *a++ = *b; *b++ = tmp;
+ } while ( --nints );
+}
+
+#endif
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