Make g_qsort_with_data stable, based on glibc msort

We need a stable sort, and we might as well always use it rather
than have multiple sort versions. This picks up the glibc
merge sort implementation which it uses by default for qsort,
except we don't fall back to non-stable quicksort in some cases
like glibc

https://bugzilla.gnome.org/show_bug.cgi?id=672095

1 files changed, 250 insertions, 244 deletions

diff --git a/glib/gqsort.c b/glib/gqsort.c
index db4bed21e..9463124a7 100644
--- a/glib/gqsort.c
+++ b/glib/gqsort.c
@@ -19,282 +19,288 @@
  * Boston, MA 02111-1307, USA.
  */
 
-/*
- * This file was originally part of the GNU C Library, and was modified to allow
- * user data to be passed in to the sorting function.
- *
- * Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
- * Modified by Maciej Stachowiak (mjs@eazel.com)
- *
- * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
- * file for a list of people on the GLib Team.  See the ChangeLog
- * files for a list of changes.  These files are distributed with GLib
- * at ftp://ftp.gtk.org/pub/gtk/.
- */
-
 #include "config.h"
 
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
+#include "galloca.h"
+#include "gmem.h"
 
 #include "gqsort.h"
 
 #include "gtestutils.h"
 
-#ifdef HAVE_QSORT_R
-
-/**
- * g_qsort_with_data:
- * @pbase: start of array to sort
- * @total_elems: elements in the array
- * @size: size of each element
- * @compare_func: function to compare elements
- * @user_data: data to pass to @compare_func
- *
- * This is just like the standard C qsort() function, but
- * the comparison routine accepts a user data argument.
- */
-void
-g_qsort_with_data (gconstpointer    pbase,
-                   gint             total_elems,
-                   gsize            size,
-                   GCompareDataFunc compare_func,
-                   gpointer         user_data)
-{
-  qsort_r ((gpointer)pbase, total_elems, size, compare_func, user_data);
-}
-
-#else
+/* This file was originally from stdlib/msort.c in gnu libc, just changed
+   to build inside glib and to not fall back to an unstable quicksort
+   for large arrays. */
 
-/* Byte-wise swap two items of size SIZE. */
-#define SWAP(a, b, size)						      \
-  do									      \
-    {									      \
-      register size_t __size = (size);					      \
-      register char *__a = (a), *__b = (b);				      \
-      do								      \
-	{								      \
-	  char __tmp = *__a;						      \
-	  *__a++ = *__b;						      \
-	  *__b++ = __tmp;						      \
-	} while (--__size > 0);						      \
-    } while (0)
+/* An alternative to qsort, with an identical interface.
+   This file is part of the GNU C Library.
+   Copyright (C) 1992,95-97,99,2000,01,02,04,07 Free Software Foundation, Inc.
+   Written by Mike Haertel, September 1988.
 
-/* 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
+   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.
 
-/* Stack node declarations used to store unfulfilled partition obligations. */
-typedef struct
-  {
-    char *lo;
-    char *hi;
-  } stack_node;
+   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.
 
-/* 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)
+   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/>.  */
 
 
-/* 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)!  */
-
-void
-g_qsort_with_data (gconstpointer    pbase,
-		   gint             total_elems,
-		   gsize            size,
-		   GCompareDataFunc compare_func,
-		   gpointer         user_data)
+struct msort_param
 {
-  register char *base_ptr = (char *) pbase;
+  size_t s;
+  size_t var;
+  GCompareDataFunc cmp;
+  void *arg;
+  char *t;
+};
 
-  const size_t max_thresh = MAX_THRESH * size;
+static void msort_with_tmp (const struct msort_param *p, void *b, size_t n);
 
-  g_return_if_fail (total_elems >= 0);
-  g_return_if_fail (pbase != NULL || total_elems == 0);
-  g_return_if_fail (compare_func != NULL);
+static void
+msort_with_tmp (const struct msort_param *p, void *b, size_t n)
+{
+  char *b1, *b2;
+  size_t n1, n2;
 
-  if (total_elems == 0)
-    /* Avoid lossage with unsigned arithmetic below.  */
+  if (n <= 1)
     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);
+  n1 = n / 2;
+  n2 = n - n1;
+  b1 = b;
+  b2 = (char *) b + (n1 * p->s);
 
-      while (STACK_NOT_EMPTY)
-        {
-          char *left_ptr;
-          char *right_ptr;
+  msort_with_tmp (p, b1, n1);
+  msort_with_tmp (p, b2, n2);
 
-	  /* 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 ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
-	    SWAP (mid, lo, size);
-	  if ((*compare_func) ((void *) hi, (void *) mid, user_data) < 0)
-	    SWAP (mid, hi, size);
+  char *tmp = p->t;
+  const size_t s = p->s;
+  GCompareDataFunc cmp = p->cmp;
+  void *arg = p->arg;
+  switch (p->var)
+    {
+    case 0:
+      while (n1 > 0 && n2 > 0)
+	{
+	  if ((*cmp) (b1, b2, arg) <= 0)
+	    {
+	      *(guint32 *) tmp = *(guint32 *) b1;
+	      b1 += sizeof (guint32);
+	      --n1;
+	    }
 	  else
-	    goto jump_over;
-	  if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 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 ((*compare_func) ((void *) left_ptr, (void *) mid, user_data) < 0)
-		left_ptr += size;
-
-	      while ((*compare_func) ((void *) mid, (void *) right_ptr, user_data) < 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;
-		}
+	      *(guint32 *) tmp = *(guint32 *) b2;
+	      b2 += sizeof (guint32);
+	      --n2;
 	    }
-	  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;
-            }
-        }
+	  tmp += sizeof (guint32);
+	}
+      break;
+    case 1:
+      while (n1 > 0 && n2 > 0)
+	{
+	  if ((*cmp) (b1, b2, arg) <= 0)
+	    {
+	      *(guint64 *) tmp = *(guint64 *) b1;
+	      b1 += sizeof (guint64);
+	      --n1;
+	    }
+	  else
+	    {
+	      *(guint64 *) tmp = *(guint64 *) b2;
+	      b2 += sizeof (guint64);
+	      --n2;
+	    }
+	  tmp += sizeof (guint64);
+	}
+      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)
+	    {
+	      memcpy (tmp, b1, s);
+	      tmp += s;
+	      b1 += s;
+	      --n1;
+	    }
+	  else
+	    {
+	      mempcpy (tmp, b2, s);
+	      tmp += s;
+	      b2 += s;
+	      --n2;
+	    }
+	}
+      break;
     }
 
-  /* 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);
-    register 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 ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 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.  */
+  if (n1 > 0)
+    memcpy (tmp, b1, n1 * s);
+  memcpy (b, p->t, (n - n2) * s);
+}
 
-    run_ptr = base_ptr + size;
-    while ((run_ptr += size) <= end_ptr)
-      {
-	tmp_ptr = run_ptr - size;
-	while ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 0)
-	  tmp_ptr -= size;
 
-	tmp_ptr += size;
-        if (tmp_ptr != run_ptr)
-          {
-            char *trav;
+static void
+msort_r (void *b, size_t n, size_t s, GCompareDataFunc 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 = g_alloca (size);
+  else
+    {
+      /* It's large, so malloc it.  */
+      tmp = g_malloc (size);
+      p.t = tmp;
+    }
 
-	    trav = run_ptr + size;
-	    while (--trav >= run_ptr)
-              {
-                char c = *trav;
-                char *hi, *lo;
+  p.s = s;
+  p.var = 4;
+  p.cmp = cmp;
+  p.arg = arg;
 
-                for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
-                  *hi = *lo;
-                *hi = c;
-              }
-          }
-      }
-  }
+  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 (guint32) - 1)) == 0
+	  && ((char *) b - (char *) 0) % ALIGNOF_GUINT32 == 0)
+	{
+	  if (s == sizeof (guint32))
+	    p.var = 0;
+	  else if (s == sizeof (guint64)
+		   && ((char *) b - (char *) 0) % ALIGNOF_GUINT64 == 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);
+    }
+  g_free (tmp);
 }
 
-#endif /* HAVE_QSORT_R */
+/**
+ * g_qsort_with_data:
+ * @pbase: start of array to sort
+ * @total_elems: elements in the array
+ * @size: size of each element
+ * @compare_func: function to compare elements
+ * @user_data: data to pass to @compare_func
+ *
+ * This is just like the standard C qsort() function, but
+ * the comparison routine accepts a user data argument.
+ *
+ * This is guaranteed to be a stable sort since version 2.32.
+ */
+void
+g_qsort_with_data (gconstpointer    pbase,
+                   gint             total_elems,
+                   gsize            size,
+                   GCompareDataFunc compare_func,
+                   gpointer         user_data)
+{
+  return msort_r (pbase, total_elems, size, compare_func, user_data);
+}