add qsort implementation.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1036 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/libc/minilibc/qsort.c

+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+#include <stdlib.h>
+
+static void exch(char* base,size_t size,size_t a,size_t b) {
+  char* x=base+a*size;
+  char* y=base+b*size;
+  while (size) {
+    char z=*x;
+    *x=*y;
+    *y=z;
+    --size; ++x; ++y;
+  }
+}
+
+/* Quicksort with 3-way partitioning, ala Sedgewick */
+/* Blame him for the scary variable names */
+/* http://www.cs.princeton.edu/~rs/talks/QuicksortIsOptimal.pdf */
+static void quicksort(char* base,size_t size,ssize_t l,ssize_t r,
+		      int (*compar)(const void*,const void*)) {
+  ssize_t i=l-1, j=r, p=l-1, q=r, k;
+  char* v=base+r*size;
+  if (r<=l) return;
+  for (;;) {
+    while (++i != r && compar(base+i*size,v)<0) ;
+    while (compar(v,base+(--j)*size)<0) if (j == l) break;
+    if (i >= j) break;
+    exch(base,size,i,j);
+    if (compar(base+i*size,v)==0) exch(base,size,++p,i);
+    if (compar(v,base+j*size)==0) exch(base,size,j,--q);
+  }
+  exch(base,size,i,r); j = i-1; ++i;
+  for (k=l; k<p; k++, j--) exch(base,size,k,j);
+  for (k=r-1; k>q; k--, i++) exch(base,size,i,k);
+  quicksort(base,size,l,j,compar);
+  quicksort(base,size,i,r,compar);
+}
+
+void qsort(void* base,size_t nmemb,size_t size,int (*compar)(const void*,const void*)) {
+  /* check for integer overflows */
+  if (nmemb >= (((size_t)-1)>>1) ||
+      size >= (((size_t)-1)>>1)) return;
+  if (nmemb>1)
+    quicksort(base,size,0,nmemb-1,compar);
+}

components/libc/minilibc/stdlib.h

@@ -15,6 +15,8 @@
 #ifndef __STDLIB_H__
 #define __STDLIB_H__
 
+#include <sys/types.h>
+
 #if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
 int atoi(const char *nptr);
 #endif
@@ -28,4 +30,6 @@ int rand(void);
 int rand_r(unsigned int *seed);
 void srand(unsigned int seed);
 
+void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
+
 #endif

components/libc/minilibc/sys/types.h

@@ -5,6 +5,7 @@
 
 typedef long    	off_t;
 typedef rt_size_t 	size_t;
+typedef signed long ssize_t;		/* Used for a count of bytes or an error indication. */
 
 typedef rt_uint8_t 	u_char;
 typedef rt_uint16_t u_short;