-// ----------------------------------------------------------------------------
-// $Id$
-// ----------------------------------------------------------------------------
-// Public Domain C Library - http://pdclib.sourceforge.net
-// This code is Public Domain. Use, modify, and redistribute at will.
-// ----------------------------------------------------------------------------
-
-// TODO: C/C++ linkage
-void qsort( void * base, size_t nelem, size_t size, int (*cmp) ( const void * e1, const void * e2) ) { /* TODO */ };
+/* qsort( void *, size_t, size_t, int(*)( const void *, const void * ) )
+
+ This file is part of the Public Domain C Library (PDCLib).
+ Permission is granted to use, modify, and / or redistribute at will.
+*/
+
+#include <stdlib.h>
+
+#ifndef REGTEST
+
+/* This implementation is taken from Paul Edward's PDPCLIB.
+
+ Original code is credited to Raymond Gardner, Englewood CO.
+ Minor mods are credited to Paul Edwards.
+ Some reformatting and simplification done by Martin Baute.
+ All code is still Public Domain.
+*/
+
+/* Wrapper for _PDCLIB_memswp protects against multiple argument evaluation. */
+static inline void memswp( char * i, char * j, size_t size )
+{
+ _PDCLIB_memswp( i, j, size );
+}
+
+/* For small sets, insertion sort is faster than quicksort.
+ T is the threshold below which insertion sort will be used.
+ Must be 3 or larger.
+*/
+#define T 7
+
+/* Macros for handling the QSort stack */
+#define PREPARE_STACK char * stack[STACKSIZE]; char * * stackptr = stack
+#define PUSH( base, limit ) stackptr[0] = base; stackptr[1] = limit; stackptr += 2
+#define POP( base, limit ) stackptr -= 2; base = stackptr[0]; limit = stackptr[1]
+/* TODO: Stack usage is log2( nmemb ) (minus what T shaves off the worst case).
+ Worst-case nmemb is platform dependent and should probably be
+ configured through _PDCLIB_config.h.
+*/
+#define STACKSIZE 64
+
+void qsort( void * base, size_t nmemb, size_t size, int (*compar)( const void *, const void * ) )
+{
+ char * i;
+ char * j;
+ _PDCLIB_size_t thresh = T * size;
+ char * base_ = (char *)base;
+ char * limit = base_ + nmemb * size;
+ PREPARE_STACK;
+
+ for ( ;; )
+ {
+ if ( (size_t)( limit - base_ ) > thresh ) /* QSort for more than T elements. */
+ {
+ /* We work from second to last - first will be pivot element. */
+ i = base_ + size;
+ j = limit - size;
+ /* We swap first with middle element, then sort that with second
+ and last element so that eventually first element is the median
+ of the three - avoiding pathological pivots.
+ TODO: Instead of middle element, chose one randomly.
+ */
+ memswp( ( ( ( (size_t)( limit - base_ ) ) / size ) / 2 ) * size + base_, base_, size );
+ if ( compar( i, j ) > 0 ) memswp( i, j, size );
+ if ( compar( base_, j ) > 0 ) memswp( base_, j, size );
+ if ( compar( i, base_ ) > 0 ) memswp( i, base_, size );
+ /* Now we have the median for pivot element, entering main Quicksort. */
+ for ( ;; )
+ {
+ do
+ {
+ /* move i right until *i >= pivot */
+ i += size;
+ } while ( compar( i, base_ ) < 0 );
+ do
+ {
+ /* move j left until *j <= pivot */
+ j -= size;
+ } while ( compar( j, base_ ) > 0 );
+ if ( i > j )
+ {
+ /* break loop if pointers crossed */
+ break;
+ }
+ /* else swap elements, keep scanning */
+ memswp( i, j, size );
+ }
+ /* move pivot into correct place */
+ memswp( base_, j, size );
+ /* larger subfile base / limit to stack, sort smaller */
+ if ( j - base_ > limit - i )
+ {
+ /* left is larger */
+ PUSH( base_, j );
+ base_ = i;
+ }
+ else
+ {
+ /* right is larger */
+ PUSH( i, limit );
+ limit = j;
+ }
+ }
+ else /* insertion sort for less than T elements */
+ {
+ for ( j = base_, i = j + size; i < limit; j = i, i += size )
+ {
+ for ( ; compar( j, j + size ) > 0; j -= size )
+ {
+ memswp( j, j + size, size );
+ if ( j == base_ )
+ {
+ break;
+ }
+ }
+ }
+ if ( stackptr != stack ) /* if any entries on stack */
+ {
+ POP( base_, limit );
+ }
+ else /* else stack empty, done */
+ {
+ break;
+ }
+ }
+ }
+}
+
+#endif
+
+#ifdef TEST
+#include "_PDCLIB_test.h"
+#include <string.h>
+#include <limits.h>
+
+static int compare( const void * left, const void * right )
+{
+ return *( (unsigned char *)left ) - *( (unsigned char *)right );
+}
+
+int main( void )
+{
+ char presort[] = { "shreicnyjqpvozxmbt" };
+ char sorted1[] = { "bcehijmnopqrstvxyz" };
+ char sorted2[] = { "bticjqnyozpvreshxm" };
+ char s[19];
+ strcpy( s, presort );
+ qsort( s, 18, 1, compare );
+ TESTCASE( strcmp( s, sorted1 ) == 0 );
+ strcpy( s, presort );
+ qsort( s, 9, 2, compare );
+ TESTCASE( strcmp( s, sorted2 ) == 0 );
+ strcpy( s, presort );
+ qsort( s, 1, 1, compare );
+ TESTCASE( strcmp( s, presort ) == 0 );
+#if defined(REGTEST) && (__BSD_VISIBLE || __APPLE__)
+ puts( "qsort.c: Skipping test #4 for BSD as it goes into endless loop here." );
+#else
+ qsort( s, 100, 0, compare );
+ TESTCASE( strcmp( s, presort ) == 0 );
+#endif
+ return TEST_RESULTS;
+}
+
+#endif
projects / pdclib / blobdiff