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/* Sorting algorithms.
Copyright (C) 2000 Free Software Foundation, Inc.
Contributed by Mark Mitchell <>.
This file is part of GNU CC.
GNU CC 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 2, or (at your option)
any later version.
GNU CC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING. If not, write to
the Free Software Foundation, 51 Franklin Street - Fifth Floor,
Boston, MA 02110-1301, USA. */
#include "config.h"
#include "libiberty.h"
#include "sort.h"
#include <limits.h>
#include <sys/param.h>
#include <stdlib.h>
#include <string.h>
#ifndef UCHAR_MAX
#define UCHAR_MAX ((unsigned char)(-1))
/* POINTERS and WORK are both arrays of N pointers. When this
function returns POINTERS will be sorted in ascending order. */
void sort_pointers (size_t n, void **pointers, void **work)
/* The type of a single digit. This can be any unsigned integral
type. When changing this, DIGIT_MAX should be changed as
well. */
typedef unsigned char digit_t;
/* The maximum value a single digit can have. */
#define DIGIT_MAX (UCHAR_MAX + 1)
/* The Ith entry is the number of elements in *POINTERSP that have I
in the digit on which we are currently sorting. */
unsigned int count[DIGIT_MAX];
/* Nonzero if we are running on a big-endian machine. */
int big_endian_p;
size_t i;
size_t j;
/* The algorithm used here is radix sort which takes time linear in
the number of elements in the array. */
/* The algorithm here depends on being able to swap the two arrays
an even number of times. */
if ((sizeof (void *) / sizeof (digit_t)) % 2 != 0)
abort ();
/* Figure out the endianness of the machine. */
for (i = 0, j = 0; i < sizeof (size_t); ++i)
j *= (UCHAR_MAX + 1);
j += i;
big_endian_p = (((char *)&j)[0] == 0);
/* Move through the pointer values from least significant to most
significant digits. */
for (i = 0; i < sizeof (void *) / sizeof (digit_t); ++i)
digit_t *digit;
digit_t *bias;
digit_t *top;
unsigned int *countp;
void **pointerp;
/* The offset from the start of the pointer will depend on the
endianness of the machine. */
if (big_endian_p)
j = sizeof (void *) / sizeof (digit_t) - i;
j = i;
/* Now, perform a stable sort on this digit. We use counting
sort. */
memset (count, 0, DIGIT_MAX * sizeof (unsigned int));
/* Compute the address of the appropriate digit in the first and
one-past-the-end elements of the array. On a little-endian
machine, the least-significant digit is closest to the front. */
bias = ((digit_t *) pointers) + j;
top = ((digit_t *) (pointers + n)) + j;
/* Count how many there are of each value. At the end of this
loop, COUNT[K] will contain the number of pointers whose Ith
digit is K. */
for (digit = bias;
digit < top;
digit += sizeof (void *) / sizeof (digit_t))
/* Now, make COUNT[K] contain the number of pointers whose Ith
digit is less than or equal to K. */
for (countp = count + 1; countp < count + DIGIT_MAX; ++countp)
*countp += countp[-1];
/* Now, drop the pointers into their correct locations. */
for (pointerp = pointers + n - 1; pointerp >= pointers; --pointerp)
work[--count[((digit_t *) pointerp)[j]]] = *pointerp;
/* Swap WORK and POINTERS so that POINTERS contains the sorted
array. */
pointerp = pointers;
pointers = work;
work = pointerp;
/* Everything below here is a unit test for the routines in this
file. */
#ifdef UNIT_TEST
#include <stdio.h>
void *xmalloc (size_t n)
return malloc (n);
int main (int argc, char **argv)
int k;
int result;
size_t i;
void **pointers;
void **work;
if (argc > 1)
k = atoi (argv[1]);
k = 10;
pointers = XNEWVEC (void*, k);
work = XNEWVEC (void*, k);
for (i = 0; i < k; ++i)
pointers[i] = (void *) random ();
printf ("%x\n", pointers[i]);
sort_pointers (k, pointers, work);
printf ("\nSorted\n\n");
result = 0;
for (i = 0; i < k; ++i)
printf ("%x\n", pointers[i]);
if (i > 0 && (char*) pointers[i] < (char*) pointers[i - 1])
result = 1;
free (pointers);
free (work);
return result;