


/* sort.c  Sort without allocating memory




Copyright (C) 20122021 Free Software Foundation, Inc.




Written by Ian Lance Taylor, Google.








Redistribution and use in source and binary forms, with or without




modification, are permitted provided that the following conditions are




met:








(1) Redistributions of source code must retain the above copyright




notice, this list of conditions and the following disclaimer.








(2) Redistributions in binary form must reproduce the above copyright




notice, this list of conditions and the following disclaimer in




the documentation and/or other materials provided with the




distribution.








(3) The name of the author may not be used to




endorse or promote products derived from this software without




specific prior written permission.








THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR




IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED




WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE




DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,




INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES




(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR




SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)




HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,




STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING




IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE




POSSIBILITY OF SUCH DAMAGE. */








#include "config.h"








#include <stddef.h>




#include <sys/types.h>








#include "backtrace.h"




#include "internal.h"








/* The GNU glibc version of qsort allocates memory, which we must not




do if we are invoked by a signal handler. So provide our own




sort. */








static void




swap (char *a, char *b, size_t size)




{




size_t i;








for (i = 0; i < size; i++, a++, b++)




{




char t;








t = *a;




*a = *b;




*b = t;




}




}








void




backtrace_qsort (void *basearg, size_t count, size_t size,




int (*compar) (const void *, const void *))




{




char *base = (char *) basearg;




size_t i;




size_t mid;








tail_recurse:




if (count < 2)




return;








/* The symbol table and DWARF tables, which is all we use this




routine for, tend to be roughly sorted. Pick the middle element




in the array as our pivot point, so that we are more likely to




cut the array in half for each recursion step. */




swap (base, base + (count / 2) * size, size);








mid = 0;




for (i = 1; i < count; i++)




{




if ((*compar) (base, base + i * size) > 0)




{




++mid;




if (i != mid)




swap (base + mid * size, base + i * size, size);




}




}








if (mid > 0)




swap (base, base + mid * size, size);








/* Recurse with the smaller array, loop with the larger one. That




ensures that our maximum stack depth is log count. */




if (2 * mid < count)




{




backtrace_qsort (base, mid, size, compar);




base += (mid + 1) * size;




count = mid + 1;




goto tail_recurse;




}




else




{




backtrace_qsort (base + (mid + 1) * size, count  (mid + 1),




size, compar);




count = mid;




goto tail_recurse;




}




}
