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60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
/* Copyright (c) 2000, 2007 MySQL AB
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Use is subject to license terms
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
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/*
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Radixsort for pointers to fixed length strings.
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A very quick sort for not too long (< 20 char) strings.
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Needs extra buffers of number_of_elements pointers but is
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2-3 times faster than quicksort
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*/
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#include "mysys_priv.h"
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#include <m_string.h>
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/* Radixsort */
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my_bool radixsort_is_applicable(uint n_items, size_t size_of_element)
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{
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return size_of_element <= 20 && n_items >= 1000 && n_items < 100000;
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}
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void radixsort_for_str_ptr(uchar **base, uint number_of_elements, size_t size_of_element, uchar **buffer)
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{
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uchar **end,**ptr,**buffer_ptr;
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uint32 *count_ptr,*count_end,count[256];
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int pass;
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end=base+number_of_elements; count_end=count+256;
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for (pass=(int) size_of_element-1 ; pass >= 0 ; pass--)
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{
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bzero((uchar*) count,sizeof(uint32)*256);
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for (ptr= base ; ptr < end ; ptr++)
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count[ptr[0][pass]]++;
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if (count[0] == number_of_elements)
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goto next;
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for (count_ptr=count+1 ; count_ptr < count_end ; count_ptr++)
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{
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if (*count_ptr == number_of_elements)
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goto next;
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(*count_ptr)+= *(count_ptr-1);
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}
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for (ptr= end ; ptr-- != base ;)
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buffer[--count[ptr[0][pass]]]= *ptr;
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for (ptr=base, buffer_ptr=buffer ; ptr < end ;)
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(*ptr++) = *buffer_ptr++;
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next:;
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}
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}
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