## クイックソート関数の改良

#### 解説

Microsoftが用意しているqsort関数はパラメータを渡すことができないためちょっと不便。
そこで比較用関数にvoid*を渡せるように改良。

せっかくだからCStringArrayに格納されている文字列を昇順に並べ替える関数も追加。

・使用時には以下の宣言を使用
```
void __cdecl QuickSort(void *base,unsigned num,unsigned width,int (__cdecl *comp)(const void *, const void *,void*),void* lpParam);
bool	SortStringArray(CStringArray& astrText);
```

・変更後のqsort.c
```/***
*qsort.c - quicksort algorithm; qsort() library function for sorting arrays
*
*
*Purpose:
*       To implement the qsort() routine for sorting arrays.
*
*******************************************************************************/

#include "stdafx.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

///////////////////////////////////////////////////
//使用時は以下の宣言を使用すること
/*
void __cdecl QuickSort(void *base,unsigned num,unsigned width,int (__cdecl *comp)(const void *, const void *,void*),void* lpParam);
bool	SortStringArray(CStringArray& astrText);
*/
//
///////////////////////////////////////////////////

/* prototypes for local routines */
static void __cdecl shortsort(char *lo, char *hi, unsigned width,int (__cdecl *comp)(const void*, const void*,void*),void* lpParam);
static void __cdecl swap(char *p, char *q, unsigned int width);

/* this parameter defines the cutoff between using quick sort and
insertion sort for arrays; arrays with lengths shorter or equal to the
below value use insertion sort */

#define CUTOFF 8            /* testing shows that this is good value */

//
//	SortStringArray()用の比較関数
//
int __cdecl SortStringArray(const void * lpData1, const void * lpData2,void* lpParam)
{
DWORD		nData1;
DWORD		nData2;

nData1 = *(DWORD*)lpData1;
nData2 = *(DWORD*)lpData2;

CStringArray*	lpastrFile;

lpastrFile = (CStringArray*) lpParam;

return	strcmp(lpastrFile->GetAt((int)nData1),lpastrFile->GetAt((int)nData2));
}

//
//	文字列の並べ替え関数
//
//		CStringArrayを昇順に並べ替える
//
bool	SortStringArray(CStringArray& astrText)
{
TRY
{
int				i;
int				nCount;
DWORD*			lpnIndex;
CStringArray	astrTemp;

nCount = astrText.GetSize();

lpnIndex = new DWORD[nCount + 1];

for(i = 0; i < nCount; i++)
lpnIndex[i] = i;

QuickSort(lpnIndex,nCount,sizeof(DWORD),SortStringArray,&astrText);

for(i = 0; i < nCount; i++)

delete	lpnIndex;

astrText.RemoveAll();
for(i = 0; i < nCount; i++)
}
CATCH_ALL(e)
return	false;
END_CATCH_ALL

return	true;
}

/***
*qsort(base, num, wid, comp) - quicksort function for sorting arrays
*
*Purpose:
*       quicksort the array of elements
*       side effects:  sorts in place
*
*Entry:
*       char *base = pointer to base of array
*       unsigned num  = number of elements in the array
*       unsigned width = width in bytes of each array element
*       int (*comp)() = pointer to function returning analog of strcmp for
*               strings, but supplied by user for comparing the array elements.
*               it accepts 2 pointers to elements and returns neg if 1<2, 0 if
*               1=2, pos if 1>2.
*
*Exit:
*       returns void
*
*Exceptions:
*
*******************************************************************************/

/* sort the array between lo and hi (inclusive) */

void __cdecl QuickSort(void *base,unsigned num,unsigned width,int (__cdecl *comp)(const void *, const void *,void*),void* lpParam)
{
char *lo, *hi;              /* ends of sub-array currently sorting */
char *mid;                  /* points to middle of subarray */
char *loguy, *higuy;        /* traveling pointers for partition step */
unsigned size;              /* size of the sub-array */
char *lostk, *histk;
int stkptr;                 /* stack for saving sub-array to be processed */

/* Note: the number of stack entries required is no more than
1 + log2(size), so 30 is sufficient for any array */

if (num < 2 || width == 0)
return;                 /* nothing to do */

stkptr = 0;                 /* initialize stack */

lo = (char*)base;
hi = (char*)base + width * (num-1);        /* initialize limits */

/* this entry point is for pseudo-recursion calling: setting
lo and hi and jumping to here is like recursion, but stkptr is
prserved, locals aren't, so we preserve stuff on the stack */
recurse:

size = (hi - lo) / width + 1;        /* number of el's to sort */

/* below a certain size, it is faster to use a O(n^2) sorting method */
if (size <= CUTOFF) {
shortsort(lo, hi, width, comp,lpParam);
}
else {
/* First we pick a partititioning element.  The efficiency of the
algorithm demands that we find one that is approximately the
median of the values, but also that we select one fast.  Using
sorted, so we use the middle one, which would require a very
wierdly arranged array for worst case performance.  Testing shows
that a median-of-three algorithm does not, in general, increase
performance. */

mid = lo + (size / 2) * width;      /* find middle element */
swap(mid, lo, width);               /* swap it to beginning of array */

/* We now wish to partition the array into three pieces, one
consisiting of elements <= partition element, one of elements
equal to the parition element, and one of element >= to it.  This
is done below; comments indicate conditions established at every
step. */

loguy = lo;
higuy = hi + width;

/* Note that higuy decreases and loguy increases on every iteration,
so loop must terminate. */
for (;;) {
/* lo <= loguy < hi, lo < higuy <= hi + 1,
A[i] <= A[lo] for lo <= i <= loguy,
A[i] >= A[lo] for higuy <= i <= hi */

do  {
loguy += width;
} while (loguy <= hi && comp(loguy, lo,lpParam) <= 0);

/* lo < loguy <= hi+1, A[i] <= A[lo] for lo <= i < loguy,
either loguy > hi or A[loguy] > A[lo] */

do  {
higuy -= width;
} while (higuy > lo && comp(higuy, lo,lpParam) >= 0);

/* lo-1 <= higuy <= hi, A[i] >= A[lo] for higuy < i <= hi,
either higuy <= lo or A[higuy] < A[lo] */

if (higuy < loguy)
break;

/* if loguy > hi or higuy <= lo, then we would have exited, so
A[loguy] > A[lo], A[higuy] < A[lo],
loguy < hi, highy > lo */

swap(loguy, higuy, width);

/* A[loguy] < A[lo], A[higuy] > A[lo]; so condition at top
of loop is re-established */
}

/*     A[i] >= A[lo] for higuy < i <= hi,
A[i] <= A[lo] for lo <= i < loguy,
higuy < loguy, lo <= higuy <= hi
implying:
A[i] >= A[lo] for loguy <= i <= hi,
A[i] <= A[lo] for lo <= i <= higuy,
A[i] = A[lo] for higuy < i < loguy */

swap(lo, higuy, width);     /* put partition element in place */

/* OK, now we have the following:
A[i] >= A[higuy] for loguy <= i <= hi,
A[i] <= A[higuy] for lo <= i < higuy
A[i] = A[lo] for higuy <= i < loguy    */

/* We've finished the partition, now we want to sort the subarrays
[lo, higuy-1] and [loguy, hi].
We do the smaller one first to minimize stack usage.
We only sort arrays of length 2 or more.*/

if ( higuy - 1 - lo >= hi - loguy ) {
if (lo + width < higuy) {
lostk[stkptr] = lo;
histk[stkptr] = higuy - width;
++stkptr;
}                           /* save big recursion for later */

if (loguy < hi) {
lo = loguy;
goto recurse;           /* do small recursion */
}
}
else {
if (loguy < hi) {
lostk[stkptr] = loguy;
histk[stkptr] = hi;
++stkptr;               /* save big recursion for later */
}

if (lo + width < higuy) {
hi = higuy - width;
goto recurse;           /* do small recursion */
}
}
}

/* We have sorted the array, except for any pending sorts on the stack.
Check if there are any, and do them. */

--stkptr;
if (stkptr >= 0) {
lo = lostk[stkptr];
hi = histk[stkptr];
goto recurse;           /* pop subarray from stack */
}
else
return;                 /* all subarrays done */
}

/***
*shortsort(hi, lo, width, comp) - insertion sort for sorting short arrays
*
*Purpose:
*       sorts the sub-array of elements between lo and hi (inclusive)
*       side effects:  sorts in place
*       assumes that lo < hi
*
*Entry:
*       char *lo = pointer to low element to sort
*       char *hi = pointer to high element to sort
*       unsigned width = width in bytes of each array element
*       int (*comp)() = pointer to function returning analog of strcmp for
*               strings, but supplied by user for comparing the array elements.
*               it accepts 2 pointers to elements and returns neg if 1<2, 0 if
*               1=2, pos if 1>2.
*
*Exit:
*       returns void
*
*Exceptions:
*
*******************************************************************************/

static void __cdecl shortsort (
char *lo,
char *hi,
unsigned width,
int (__cdecl *comp)(const void *, const void *,void *),void* lpParam
)
{
char *p, *max;

/* Note: in assertions below, i and j are alway inside original bound of
array to sort. */

while (hi > lo) {
/* A[i] <= A[j] for i <= j, j > hi */
max = lo;
for (p = lo+width; p <= hi; p += width) {
/* A[i] <= A[max] for lo <= i < p */
if (comp(p, max,lpParam) > 0) {
max = p;
}
/* A[i] <= A[max] for lo <= i <= p */
}

/* A[i] <= A[max] for lo <= i <= hi */

swap(max, hi, width);

/* A[i] <= A[hi] for i <= hi, so A[i] <= A[j] for i <= j, j >= hi */

hi -= width;

/* A[i] <= A[j] for i <= j, j > hi, loop top condition established */
}
/* A[i] <= A[j] for i <= j, j > lo, which implies A[i] <= A[j] for i < j,
so array is sorted */
}

/***
*swap(a, b, width) - swap two elements
*
*Purpose:
*       swaps the two array elements of size width
*
*Entry:
*       char *a, *b = pointer to two elements to swap
*       unsigned width = width in bytes of each array element
*
*Exit:
*       returns void
*
*Exceptions:
*
*******************************************************************************/

static void __cdecl swap (
char *a,
char *b,
unsigned width
)
{
char tmp;

if ( a != b )
/* Do the swap one character at a time to avoid potential alignment
problems. */
while ( width-- ) {
tmp = *a;
*a++ = *b;
*b++ = tmp;
}
}
```