[7/7] stdlib: Remove undefined behavior from qsort implementation

diff --git a/stdlib/qsort.c b/stdlib/qsort.c
index 2194003..03ab0e5 100644
--- a/stdlib/qsort.c
+++ b/stdlib/qsort.c
@@ -16,17 +16,13 @@ 
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* If you consider tuning this algorithm, you should consult first:
-   Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
-   Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993.  */
-
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
 
-/* Swap SIZE bytes between addresses A and B.  Helper to generic types
-   are provided as an optimization.  */
+/* Swap SIZE bytes between addresses A and B.  These helpers are provided
+   along the generic one as an optimization.  */
 
 typedef void (*swap_t)(void *, void *, size_t);
 
@@ -98,202 +94,14 @@  typedef struct
 #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)!  */
-
-void
-__qsort_r (void *const pbase, size_t total_elems, size_t size,
-	   __compar_d_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;
-
-  swap_t swap = select_swap_func (pbase, size);
-
-  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;
-              }
-          }
-      }
-  }
-}
+#define R_VERSION
+#define R_FUNC    __qsort_r
+#include <stdlib/qsort_common.c>
 
 libc_hidden_def (__qsort_r)
 weak_alias (__qsort_r, qsort_r)
 
-void
-qsort (void *b, size_t n, size_t s, __compar_fn_t cmp)
-{
-  return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL);
-}
+#define R_FUNC   qsort
+#include <stdlib/qsort_common.c>
+
 libc_hidden_def (qsort)
diff --git a/stdlib/qsort_common.c b/stdlib/qsort_common.c
new file mode 100644
index 0000000..666b195
--- /dev/null
+++ b/stdlib/qsort_common.c
@@ -0,0 +1,225 @@ 
+/* Common implementation for both qsort and qsort_r.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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/>.  */
+
+/* If you consider tuning this algorithm, you should consult first:
+   Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
+   Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993.  */
+
+#ifdef R_VERSION
+# define R_CMP_TYPE          __compar_d_fn_t
+# define R_CMP_ARG           , void *arg
+# define R_CMP(p1, p2)       cmp (p1, p2, arg)
+#else
+# define R_CMP_TYPE           __compar_fn_t
+# define R_CMP_ARG
+# define R_CMP(p1, p2)       cmp (p1, p2)
+#endif
+
+/* 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
+R_FUNC (void *pbase, size_t total_elems, size_t size, R_CMP_TYPE cmp R_CMP_ARG)
+{
+  if (total_elems == 0)
+    /* Avoid lossage with unsigned arithmetic below.  */
+    return;
+
+  char *base_ptr = (char *) pbase;
+
+  const size_t max_thresh = MAX_THRESH * size;
+
+  swap_t swap = select_swap_func (pbase, size);
+
+  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 (R_CMP ((void *) mid, (void *) lo) < 0)
+	    swap (mid, lo, size);
+	  if (R_CMP ((void *) hi, (void *) mid) < 0)
+	    swap (mid, hi, size);
+	  else
+	    goto jump_over;
+	  if (R_CMP ((void *) mid, (void *) lo) < 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 (R_CMP ((void *) left_ptr, (void *) mid) < 0)
+		left_ptr += size;
+
+	      while (R_CMP ((void *) mid, (void *) right_ptr) < 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!). */
+
+  {
+    char *const end_ptr = &base_ptr[size * (total_elems - 1)];
+    char *tmp_ptr = base_ptr;
+    char *thresh = end_ptr < base_ptr + max_thresh ?
+		   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 (R_CMP ((void *) run_ptr, (void *) tmp_ptr) < 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 (R_CMP ((void *) run_ptr, (void *) tmp_ptr) < 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;
+              }
+          }
+      }
+  }
+}
+
+#undef R_NAME
+#undef R_CMP_TYPE
+#undef R_CMP_ARG
+#undef R_CMP
+#undef R_FUNC
+#undef R_VERSION