Commit c32ee4ee authored by monty@donna.mysql.fi's avatar monty@donna.mysql.fi

New qsort implementation

parent ab9c0df7
...@@ -15,245 +15,201 @@ ...@@ -15,245 +15,201 @@
Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA */ MA 02111-1307, USA */
/* Plug-compatible replacement for UNIX qsort. /*
Copyright (C) 1989 Free Software Foundation, Inc. qsort implementation optimized for comparison of pointers
Written by Douglas C. Schmidt (schmidt@ics.uci.edu) Inspired by the qsort implementations by Douglas C. Schmidt,
Optimized and modyfied for mysys by monty. and Bentley & McIlroy's "Engineering a Sort Function".
*/
This file is part of GNU CC.
GNU QSORT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.
GNU QSORT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNU QSORT; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "mysys_priv.h" #include "mysys_priv.h"
/* Envoke the comparison function, returns either 0, < 0, or > 0. */ /* We need to use qsort with 2 different compare functions */
#ifdef QSORT_EXTRA_CMP_ARGUMENT #ifdef QSORT_EXTRA_CMP_ARGUMENT
#define CMP(A,B) ((*cmp)(cmp_argument,(A),(B))) #define CMP(A,B) ((*cmp)(cmp_argument,(A),(B)))
#else #else
#define CMP(A,B) ((*cmp)((A),(B))) #define CMP(A,B) ((*cmp)((A),(B)))
#endif #endif
/* Byte-wise swap two items of size SIZE. */ #define SWAP(A, B, size,swap_ptrs) \
#define SWAP(A,B,SIZE) do {int sz=(int)(SIZE); char *a = (A); char *b = (B); \ do { \
do { char _temp = *a;*a++ = *b;*b++ = _temp;} while (--sz);} while (0) if (swap_ptrs) \
{ \
/* Copy SIZE bytes from item B to item A. */ reg1 char **a = (char**) (A), **b = (char**) (B); \
#define COPY(A,B,SIZE) {int sz = (int) (SIZE); do { *(A)++ = *(B)++; } while (--sz); } char *tmp = *a; *a++ = *b; *b++ = tmp; \
} \
/* This should be replaced by a standard ANSI macro. */ else \
#define BYTES_PER_WORD 8 { \
reg1 char *a = (A), *b = (B); \
/* The next 4 #defines implement a very fast in-line stack abstraction. */ reg3 char *end= a+size; \
#define STACK_SIZE (BYTES_PER_WORD * sizeof (long)) do \
#define PUSH(LOW,HIGH) do {top->lo = LOW;top++->hi = HIGH;} while (0) { \
#define POP(LOW,HIGH) do {LOW = (--top)->lo;HIGH = top->hi;} while (0) char tmp = *a; *a++ = *b; *b++ = tmp; \
#define STACK_NOT_EMPTY (stack < top) } while (a < end); \
} \
} while (0)
/* Put the median in the middle argument */
#define MEDIAN(low, mid, high) \
{ \
if (CMP(high,low) < 0) \
SWAP(high, low, size, ptr_cmp); \
if (CMP(mid, low) < 0) \
SWAP(mid, low, size, ptr_cmp); \
else if (CMP(high, mid) < 0) \
SWAP(mid, high, size, ptr_cmp); \
}
/* Discontinue quicksort algorithm when partition gets below this size. /* The following node is used to store ranges to avoid recursive calls */
This particular magic number was chosen to work best on a Sparc SLC. */
#define MAX_THRESH 12
/* Stack node declarations used to store unfulfilled partition obligations. */ typedef struct st_stack
typedef struct
{ {
char *lo; char *low,*high;
char *hi; } STACK;
} stack_node;
/* Order size using quicksort. This implementation incorporates
four optimizations discussed in Sedgewick:
1. Non-recursive, using an explicit stack of pointer that store the
next array partition to sort. To save time, this maximum amount
of space required to store an array of MAX_INT is allocated on the
stack. Assuming a 32-bit integer, this needs only 32 *
sizeof (stack_node) == 136 bits. Pretty cheap, actually.
2. Chose the pivot element using a median-of-three decision tree. #define PUSH(LOW,HIGH) {stack_ptr->low = LOW; stack_ptr++->high = HIGH;}
This reduces the probability of selecting a bad pivot value and #define POP(LOW,HIGH) {LOW = (--stack_ptr)->low; HIGH = stack_ptr->high;}
eliminates certain extraneous comparisons.
3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
insertion sort to order the MAX_THRESH items within each partition.
This is a big win, since insertion sort is faster for small, mostly
sorted array segements.
4. The larger of the two sub-partitions is always pushed onto the
stack first, with the algorithm then concentrating on the
smaller partition. This *guarantees* no more than log (n)
stack size is needed (actually O(1) in this case)! */
/* The following stack size is enough for ulong ~0 elements */
#define STACK_SIZE (8 * sizeof(unsigned long int))
#define THRESHOLD_FOR_INSERT_SORT 10
#if defined(QSORT_TYPE_IS_VOID) #if defined(QSORT_TYPE_IS_VOID)
#define SORT_RETURN return #define SORT_RETURN return
#else #else
#define SORT_RETURN return 0 #define SORT_RETURN return 0
#endif #endif
/****************************************************************************
** 'standard' quicksort with the following extensions:
**
** Can be compiled with the qsort2_cmp compare function
** Store ranges on stack to avoid recursion
** Use insert sort on small ranges
** Optimize for sorting of pointers (used often by MySQL)
** Use median comparison to find partition element
*****************************************************************************/
#ifdef QSORT_EXTRA_CMP_ARGUMENT #ifdef QSORT_EXTRA_CMP_ARGUMENT
qsort_t qsort2(void *base_ptr, size_t total_elems, size_t size, qsort2_cmp cmp, qsort_t qsort2(void *base_ptr, size_t count, size_t size, qsort2_cmp cmp,
void *cmp_argument) void *cmp_argument)
#else #else
qsort_t qsort(void *base_ptr, size_t total_elems, size_t size, qsort_cmp cmp) qsort_t qsort(void *base_ptr, size_t count, size_t size, qsort_cmp cmp)
#endif #endif
{ {
/* Allocating SIZE bytes for a pivot buffer facilitates a better char *low, *high, *pivot;
algorithm below since we can do comparisons directly on the pivot. STACK stack[STACK_SIZE], *stack_ptr;
*/ my_bool ptr_cmp;
int max_thresh = (int) (MAX_THRESH * size); /* Handle the simple case first */
if (total_elems <= 1) /* This will also make the rest of the code simpler */
SORT_RETURN; /* Crashes on MSDOS if continues */ if (count <= 1)
SORT_RETURN;
if (total_elems > MAX_THRESH) low = (char*) base_ptr;
{ high = low+ size * (count - 1);
char *lo = base_ptr; stack_ptr = stack + 1;
char *hi = lo + size * (total_elems - 1);
stack_node stack[STACK_SIZE]; /* Largest size needed for 32-bit int!!! */
stack_node *top = stack + 1;
char *pivot_buffer = (char *) my_alloca ((int) size);
#ifdef HAVE_purify #ifdef HAVE_purify
/* The first element in the stack will be accessed for the last POP */
stack[0].lo=stack[0].hi=0; stack[0].lo=stack[0].hi=0;
#endif #endif
pivot = (char *) my_alloca((int) size);
ptr_cmp= size == sizeof(char*) && !((low - (char*) 0)& (sizeof(char*)-1));
while (STACK_NOT_EMPTY) /* The following loop sorts elements between high and low */
do
{ {
char *left_ptr; char *low_ptr, *high_ptr, *mid;
char *right_ptr;
count=((size_t) (high - low) / size)+1;
/* If count is small, then an insert sort is faster than qsort */
if (count < THRESHOLD_FOR_INSERT_SORT)
{ {
char *pivot = pivot_buffer; for (low_ptr = low + size; low_ptr <= high; low_ptr += size)
{ {
/* Select median value from among LO, MID, and HI. Rearrange char *ptr;
LO and HI so the three values are sorted. This lowers the for (ptr = low_ptr; ptr > low && CMP(ptr - size, ptr) > 0;
probability of picking a pathological pivot value and ptr -= size)
skips a comparison for both the LEFT_PTR and RIGHT_PTR. */ SWAP(ptr, ptr - size, size, ptr_cmp);
}
char *mid = lo + size * (((uint) (hi - lo) / (uint) size) >> 1); POP(low, high);
continue;
if (CMP(hi,lo) < 0)
SWAP (hi, lo, size);
if (CMP (mid, lo) < 0)
SWAP (mid, lo, size);
else if (CMP (hi, mid) < 0)
SWAP (mid, hi, size);
COPY (pivot, mid, size);
pivot = pivot_buffer;
} }
left_ptr = lo + size;
right_ptr = hi - size;
/* Here's the famous ``collapse the walls'' section of quicksort.
Gotta like those tight inner loops! They are the main reason
that this algorithm runs much faster than others. */
do
{
while (CMP (left_ptr, pivot) < 0)
left_ptr += size;
while (CMP (pivot, right_ptr) < 0)
right_ptr -= size;
if (left_ptr < right_ptr) /* Try to find a good middle element */
mid= low + size * (count >> 1);
if (count > 40) /* Must be bigger than 24 */
{ {
SWAP (left_ptr, right_ptr, size); size_t step = size* (count / 8);
left_ptr += size; MEDIAN(low, low + step, low+step*2);
right_ptr -= size; MEDIAN(mid - step, mid, mid+step);
MEDIAN(high - 2 * step, high-step, high);
/* Put best median in 'mid' */
MEDIAN(low+step, mid, high-step);
low_ptr = low;
high_ptr = high;
} }
else if (left_ptr == right_ptr) else
{ {
left_ptr += size; MEDIAN(low, mid, high);
right_ptr -= size; /* The low and high argument are already in sorted against 'pivot' */
break; low_ptr = low + size;
} high_ptr = high - size;
}
while (left_ptr <= right_ptr);
} }
memcpy(pivot, mid, size);
/* Set up pointers for next iteration. First determine whether do
left and right partitions are below the threshold size. If so, {
ignore one or both. Otherwise, push the larger partition's while (CMP(low_ptr, pivot) < 0)
bounds on the stack and continue sorting the smaller one. */ low_ptr += size;
while (CMP(pivot, high_ptr) < 0)
high_ptr -= size;
if ((right_ptr - lo) <= max_thresh) if (low_ptr < high_ptr)
{ {
if ((hi - left_ptr) <= max_thresh) /* Ignore both small parts. */ SWAP(low_ptr, high_ptr, size, ptr_cmp);
POP (lo, hi); low_ptr += size;
else /* Ignore small left part. */ high_ptr -= size;
lo = left_ptr;
} }
else if ((hi - left_ptr) <= max_thresh) /* Ignore small right part. */ else
hi = right_ptr;
else if ((right_ptr - lo) > (hi - left_ptr)) /* Push larger left part */
{ {
PUSH (lo, right_ptr); if (low_ptr == high_ptr)
lo = left_ptr;
}
else /* Push larger right part */
{ {
PUSH (left_ptr, hi); low_ptr += size;
hi = right_ptr; high_ptr -= size;
} }
break;
} }
my_afree(pivot_buffer);
} }
while (low_ptr <= high_ptr);
/* Once the BASE_PTR array is partially sorted by quicksort the rest /*
is completely sorted using insertion sort, since this is efficient Prepare for next iteration.
for partitions below MAX_THRESH size. BASE_PTR points to the beginning Skip partitions of size 1 as these doesn't have to be sorted
of the array to sort, and END_PTR points at the very last element in Push the larger partition and sort the smaller one first.
the array (*not* one beyond it!). */ This ensures that the stack is keept small.
*/
{
char *end_ptr = (char*) base_ptr + size * (total_elems - 1);
char *run_ptr;
char *tmp_ptr = (char*) base_ptr;
char *thresh = min (end_ptr, (char*) base_ptr + max_thresh);
/* Find smallest element in first threshold and place it at the
array's beginning. This is the smallest array element,
and the operation speeds up insertion sort's inner loop. */
for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
if (CMP (run_ptr, tmp_ptr) < 0)
tmp_ptr = run_ptr;
if (tmp_ptr != (char*) base_ptr)
SWAP (tmp_ptr, (char*) base_ptr, size);
/* Insertion sort, running from left-hand-side up to `right-hand-side.'
Pretty much straight out of the original GNU qsort routine. */
for (run_ptr = (char*) base_ptr + size; if ((int) (high_ptr - low) <= 0)
(tmp_ptr = run_ptr += size) <= end_ptr; )
{ {
while (CMP (run_ptr, tmp_ptr -= size) < 0) ; if ((int) (high - low_ptr) <= 0)
if ((tmp_ptr += size) != run_ptr)
{ {
char *trav; POP(low, high); /* Nothing more to sort */
for (trav = run_ptr + size; --trav >= run_ptr;)
{
char c = *trav;
char *hi, *lo;
for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
*hi = *lo;
*hi = c;
} }
else
low = low_ptr; /* Ignore small left part. */
} }
else if ((int) (high - low_ptr) <= 0)
high = high_ptr; /* Ignore small right part. */
else if ((high_ptr - low) > (high - low_ptr))
{
PUSH(low, high_ptr); /* Push larger left part */
low = low_ptr;
} }
else
{
PUSH(low_ptr, high); /* Push larger right part */
high = high_ptr;
} }
} while (stack_ptr > stack);
my_afree(pivot);
SORT_RETURN; SORT_RETURN;
} }
...@@ -104,7 +104,7 @@ int mysql_ha_read(THD *thd, TABLE_LIST *tables, ...@@ -104,7 +104,7 @@ int mysql_ha_read(THD *thd, TABLE_LIST *tables,
List_iterator<Item> it(list); List_iterator<Item> it(list);
it++; it++;
insert_fields(thd,tables,tables->name,&it); insert_fields(thd,tables,tables->db,tables->name,&it);
table->file->index_init(keyno); table->file->index_init(keyno);
......
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