path: root/src/shared/qsort_r_missing.c

/***
  This file is part of elogind.

  Copyright 2017-2018 Sven Eden

  elogind is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  elogind 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with elogind; If not, see <http://www.gnu.org/licenses/>.
***/

#include <stdlib.h>

#include "qsort_r_missing.h"

#if HAVE_QSORT_R == 0

#include <alloca.h>
#include <errno.h>
#include <limits.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>

/***
  Original disclaimer of glibc-2.28 msort.c concerning qsort_r() follows:
***/

/* An alternative to qsort, with an identical interface.
   This file is part of the GNU C Library.
   Copyright (C) 1992-2018 Free Software Foundation, Inc.
   Written by Mike Haertel, September 1988.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */


/* qsort_r() calls internal _quicksort() function from qsort.c. Disclaimer is as above. */
static void quicksort ( void* const pbase, size_t total_elems, size_t size, compare_fn_t cmp, void* arg );

struct msort_param {
        size_t s;
        size_t var;
        compare_fn_t cmp;
        void* arg;
        char* t;
};

static void msort_with_tmp ( const struct msort_param* p, void* b, size_t n ) {
        char* b1, *b2;
        size_t n1, n2;

        if ( n <= 1 )
                return;

        n1 = n / 2;
        n2 = n - n1;
        b1 = b;
        b2 = ( char* ) b + ( n1 * p->s );

        msort_with_tmp ( p, b1, n1 );
        msort_with_tmp ( p, b2, n2 );

        char* tmp = p->t;
        const size_t s = p->s;
        __compar_d_fn_t cmp = p->cmp;
        void* arg = p->arg;
        switch ( p->var ) {
                case 0:
                        while ( n1 > 0 && n2 > 0 ) {
                                if ( ( *cmp ) ( b1, b2, arg ) <= 0 ) {
                                        *( uint32_t* ) tmp = *( uint32_t* ) b1;
                                        b1 += sizeof ( uint32_t );
                                        --n1;
                                } else {
                                        *( uint32_t* ) tmp = *( uint32_t* ) b2;
                                        b2 += sizeof ( uint32_t );
                                        --n2;
                                }
                                tmp += sizeof ( uint32_t );
                        }
                        break;
                case 1:
                        while ( n1 > 0 && n2 > 0 ) {
                                if ( ( *cmp ) ( b1, b2, arg ) <= 0 ) {
                                        *( uint64_t* ) tmp = *( uint64_t* ) b1;
                                        b1 += sizeof ( uint64_t );
                                        --n1;
                                } else {
                                        *( uint64_t* ) tmp = *( uint64_t* ) b2;
                                        b2 += sizeof ( uint64_t );
                                        --n2;
                                }
                                tmp += sizeof ( uint64_t );
                        }
                        break;
                case 2:
                        while ( n1 > 0 && n2 > 0 ) {
                                unsigned long* tmpl = ( unsigned long* ) tmp;
                                unsigned long* bl;

                                tmp += s;
                                if ( ( *cmp ) ( b1, b2, arg ) <= 0 ) {
                                        bl = ( unsigned long* ) b1;
                                        b1 += s;
                                        --n1;
                                } else {
                                        bl = ( unsigned long* ) b2;
                                        b2 += s;
                                        --n2;
                                }
                                while ( tmpl < ( unsigned long* ) tmp )
                                        *tmpl++ = *bl++;
                        }
                        break;
                case 3:
                        while ( n1 > 0 && n2 > 0 ) {
                                if ( ( *cmp ) ( *( const void** ) b1, *( const void** ) b2, arg ) <= 0 ) {
                                        *( void** ) tmp = *( void** ) b1;
                                        b1 += sizeof ( void* );
                                        --n1;
                                } else {
                                        *( void** ) tmp = *( void** ) b2;
                                        b2 += sizeof ( void* );
                                        --n2;
                                }
                                tmp += sizeof ( void* );
                        }
                        break;
                default:
                        while ( n1 > 0 && n2 > 0 ) {
                                if ( ( *cmp ) ( b1, b2, arg ) <= 0 ) {
                                        tmp = ( char* ) memcpy ( tmp, b1, s );
                                        b1 += s;
                                        --n1;
                                } else {
                                        tmp = ( char* ) memcpy ( tmp, b2, s );
                                        b2 += s;
                                        --n2;
                                }
                        }
                        break;
        }

        if ( n1 > 0 )
                memcpy ( tmp, b1, n1 * s );
        memcpy ( b, p->t, ( n - n2 ) * s );
}

void qsort_r ( void* b, size_t n, size_t s, compare_fn_t cmp, void* arg ) {
        size_t size = n * s;
        char* tmp = NULL;
        struct msort_param p;

        /* For large object sizes use indirect sorting.  */
        if ( s > 32 )
                size = 2 * n * sizeof ( void* ) + s;

        if ( size < 1024 )
                /* The temporary array is small, so put it on the stack.  */
                p.t = alloca ( size );
        else {
                /* We should avoid allocating too much memory since this might
                have to be backed up by swap space.  */
                static long int phys_pages;
                static int pagesize;

                if ( pagesize == 0 ) {
                        phys_pages = sysconf ( _SC_PHYS_PAGES );

                        if ( phys_pages == -1 )
                                /* Error while determining the memory size.  So let's
                                   assume there is enough memory.  Otherwise the
                                   implementer should provide a complete implementation of
                                   the `sysconf' function.  */
                                phys_pages = ( long int ) ( ~0ul >> 1 );

                        /* The following determines that we will never use more than
                           a quarter of the physical memory.  */
                        phys_pages /= 4;

                        /* Make sure phys_pages is written to memory.  */
                        __asm ( "" ::: "memory" ); /*atomic_write_barrier () */

                        pagesize = sysconf ( _SC_PAGESIZE );
                }

                /* Just a comment here.  We cannot compute
                 phys_pages * pagesize
                 and compare the needed amount of memory against this value.
                 The problem is that some systems might have more physical
                 memory then can be represented with a `size_t' value (when
                 measured in bytes.  */

                /* If the memory requirements are too high don't allocate memory.  */
                if ( size / pagesize > ( size_t ) phys_pages ) {
                        quicksort ( b, n, s, cmp, arg );
                        return;
                }

                /* It's somewhat large, so malloc it.  */
                int save = errno;
                tmp = malloc ( size );
                errno = ( save );
                if ( tmp == NULL ) {
                        /* Couldn't get space, so use the slower algorithm
                           that doesn't need a temporary array.  */
                        quicksort ( b, n, s, cmp, arg );
                        return;
                }
                p.t = tmp;
        }

        p.s = s;
        p.var = 4;
        p.cmp = cmp;
        p.arg = arg;

        if ( s > 32 ) {
                /* Indirect sorting.  */
                char* ip = ( char* ) b;
                void** tp = ( void** ) ( p.t + n * sizeof ( void* ) );
                void** t = tp;
                void* tmp_storage = ( void* ) ( tp + n );

                while ( ( void* ) t < tmp_storage ) {
                        *t++ = ip;
                        ip += s;
                }
                p.s = sizeof ( void* );
                p.var = 3;
                msort_with_tmp ( &p, p.t + n * sizeof ( void* ), n );

                /* tp[0] .. tp[n - 1] is now sorted, copy around entries of
                the original array.  Knuth vol. 3 (2nd ed.) exercise 5.2-10.  */
                char* kp;
                size_t i;
                for ( i = 0, ip = ( char* ) b; i < n; i++, ip += s )
                        if ( ( kp = tp[i] ) != ip ) {
                                size_t j = i;
                                char* jp = ip;
                                memcpy ( tmp_storage, ip, s );

                                do {
                                        size_t k = ( kp - ( char* ) b ) / s;
                                        tp[j] = jp;
                                        memcpy ( jp, kp, s );
                                        j = k;
                                        jp = kp;
                                        kp = tp[k];
                                } while ( kp != ip );

                                tp[j] = jp;
                                memcpy ( jp, tmp_storage, s );
                        }
        } else {
                if ( ( s & ( sizeof ( uint32_t ) - 1 ) ) == 0
                                && ( ( char* ) b - ( char* ) 0 ) % __alignof__ ( uint32_t ) == 0 ) {
                        if ( s == sizeof ( uint32_t ) )
                                p.var = 0;
                        else if ( s == sizeof ( uint64_t )
                                        && ( ( char* ) b - ( char* ) 0 ) % __alignof__ ( uint64_t ) == 0 )
                                p.var = 1;
                        else if ( ( s & ( sizeof ( unsigned long ) - 1 ) ) == 0
                                        && ( ( char* ) b - ( char* ) 0 )
                                        % __alignof__ ( unsigned long ) == 0 )
                                p.var = 2;
                }
                msort_with_tmp ( &p, b, n );
        }
        free ( tmp );
}

/**** quicksort from qsort.c follows ****/

/* Byte-wise swap two items of size SIZE. */
#define SWAP(a, b, size)           \
  do                               \
    {                              \
      size_t __size = (size);      \
      char *__a = (a), *__b = (b); \
      do                           \
    {                              \
      char __tmp = *__a;           \
      *__a++ = *__b;               \
      *__b++ = __tmp;              \
    } while (--__size > 0);        \
    } while (0)

/* Discontinue quicksort algorithm when partition gets below this size.
   This particular magic number was chosen to work best on a Sun 4/260. */
#define MAX_THRESH 4

/* Stack node declarations used to store unfulfilled partition obligations. */
typedef struct {
        char* lo;
        char* hi;
} stack_node;

/* The next 4 #defines implement a very fast in-line stack abstraction. */
/* The stack needs log (total_elements) entries (we could even subtract
   log(MAX_THRESH)).  Since total_elements has type size_t, we get as
   upper bound for log (total_elements):
   bits per byte (CHAR_BIT) * sizeof(size_t).  */
#define STACK_SIZE      (CHAR_BIT * sizeof(size_t))
#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
#define POP(low, high)  ((void) (--top, (low = top->lo), (high = top->hi)))
#define STACK_NOT_EMPTY (stack < top)

/* 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 SIZE_MAX is allocated on the
      stack.  Assuming a 32-bit (64 bit) integer for size_t, this needs
      only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
      Pretty cheap, actually.

   2. Chose the pivot element using a median-of-three decision tree.
      This reduces the probability of selecting a bad pivot value and
      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 segments.

   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 (total_elems)
      stack size is needed (actually O(1) in this case)!  */

static void quicksort ( void* const pbase, size_t total_elems, size_t size, compare_fn_t cmp, void* arg ) {
        char* base_ptr = ( char* ) pbase;

        const size_t max_thresh = MAX_THRESH * size;

        if ( total_elems == 0 )
                /* Avoid lossage with unsigned arithmetic below.  */
                return;

        if ( total_elems > MAX_THRESH ) {
                char* lo = base_ptr;
                char* hi = &lo[size * ( total_elems - 1 )];
                stack_node stack[STACK_SIZE];
                stack_node* top = stack;

                PUSH ( NULL, NULL );

                while ( STACK_NOT_EMPTY ) {
                        char* left_ptr;
                        char* right_ptr;

                        /* Select median value from among LO, MID, and HI. Rearrange
                           LO and HI so the three values are sorted. This lowers the
                           probability of picking a pathological pivot value and
                           skips a comparison for both the LEFT_PTR and RIGHT_PTR in
                           the while loops. */

                        char* mid = lo + size * ( ( hi - lo ) / size >> 1 );

                        if ( ( *cmp ) ( ( void* ) mid, ( void* ) lo, arg ) < 0 )
                                SWAP ( mid, lo, size );
                        if ( ( *cmp ) ( ( void* ) hi, ( void* ) mid, arg ) < 0 )
                                SWAP ( mid, hi, size );
                        else
                                goto jump_over;
                        if ( ( *cmp ) ( ( void* ) mid, ( void* ) lo, arg ) < 0 )
                                SWAP ( mid, lo, size );
                        jump_over:
                        ;

                        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 ) ( ( void* ) left_ptr, ( void* ) mid, arg ) < 0 )
                                        left_ptr += size;

                                while ( ( *cmp ) ( ( void* ) mid, ( void* ) right_ptr, arg ) < 0 )
                                        right_ptr -= size;

                                if ( left_ptr < right_ptr ) {
                                        SWAP ( left_ptr, right_ptr, size );
                                        if ( mid == left_ptr )
                                                mid = right_ptr;
                                        else if ( mid == right_ptr )
                                                mid = left_ptr;
                                        left_ptr += size;
                                        right_ptr -= size;
                                } else if ( left_ptr == right_ptr ) {
                                        left_ptr += size;
                                        right_ptr -= size;
                                        break;
                                }
                        } while ( left_ptr <= right_ptr );

                        /* Set up pointers for next iteration.  First determine whether
                           left and right partitions are below the threshold size.  If so,
                           ignore one or both.  Otherwise, push the larger partition's
                           bounds on the stack and continue sorting the smaller one. */

                        if ( ( size_t ) ( right_ptr - lo ) <= max_thresh ) {
                                if ( ( size_t ) ( hi - left_ptr ) <= max_thresh )
                                        /* Ignore both small partitions. */
                                        POP ( lo, hi );
                                else
                                        /* Ignore small left partition. */
                                        lo = left_ptr;
                        } else if ( ( size_t ) ( hi - left_ptr ) <= max_thresh )
                                /* Ignore small right partition. */
                                hi = right_ptr;
                        else if ( ( right_ptr - lo ) > ( hi - left_ptr ) ) {
                                /* Push larger left partition indices. */
                                PUSH ( lo, right_ptr );
                                lo = left_ptr;
                        } else {
                                /* Push larger right partition indices. */
                                PUSH ( left_ptr, hi );
                                hi = right_ptr;
                        }
                }
        }

        /* Once the BASE_PTR array is partially sorted by quicksort the rest
           is completely sorted using insertion sort, since this is efficient
           for partitions below MAX_THRESH size. BASE_PTR points to the beginning
           of the array to sort, and END_PTR points at the very last element in
           the array (*not* one beyond it!). */

#define min(x, y) ((x) < (y) ? (x) : (y))

        {
                char* const end_ptr = &base_ptr[size * ( total_elems - 1 )];
                char* tmp_ptr = base_ptr;
                char* thresh = min( end_ptr, base_ptr + max_thresh );
                char* run_ptr;

                /* 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 ) ( ( void* ) run_ptr, ( void* ) tmp_ptr, arg ) < 0 )
                                tmp_ptr = run_ptr;

                if ( tmp_ptr != base_ptr )
                        SWAP ( tmp_ptr, base_ptr, size );

                /* Insertion sort, running from left-hand-side up to right-hand-side.  */

                run_ptr = base_ptr + size;
                while ( ( run_ptr += size ) <= end_ptr ) {
                        tmp_ptr = run_ptr - size;
                        while ( ( *cmp ) ( ( void* ) run_ptr, ( void* ) tmp_ptr, arg ) < 0 )
                                tmp_ptr -= size;

                        tmp_ptr += size;
                        if ( tmp_ptr != run_ptr ) {
                                char* trav;

                                trav = run_ptr + size;
                                while ( --trav >= run_ptr ) {
                                        char c = *trav;
                                        char* hi, *lo;

                                        for ( hi = lo = trav; ( lo -= size ) >= tmp_ptr; hi = lo )
                                                * hi = *lo;
                                        *hi = c;
                                }
                        }
                }
        }
}

#endif // HAVE_QSORT_R