[PATCH][BZ #14547] Clean up strcoll implementation

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

Hi,

This patch is a preliminary cleanup before I fix the actual
vulnerability described in pr14547.  The aim of this patch is to split
up the one big strcoll function into smaller units to consolidate
common bits and make the logic generally easier to follow.

The actual fix will follow soon in two parts, first that implements
non-caching versions of get_next_seq and do_compare if memory
allocation failed and the second that does a check for integer
overflow in request sizes for the cache arrays.

I have verified that this does not cause regressions in the testsuite.
The coverage in the testsuite for strcoll and strxfrm seemed pretty
adequate to me.  This series fixes CVE-2012-4412, so I would like them
considered for inclusion into 2.18.

Siddhesh

	[BZ #14547]
	* string/strcoll_l.c (coll_seq): New structure.
	(get_next_seq_cached): New function.
	(get_next_seq): New function.
	(do_compare): New function.
	(STRCOLL): Use GNU style definition.  Simplify implementation
	by using get_next_seq, get_next_seq_cached and do_copare.

diff --git a/string/strcoll_l.c b/string/strcoll_l.c
index ecda08f..1bb9e23 100644
--- a/string/strcoll_l.c
+++ b/string/strcoll_l.c
@@ -41,11 +41,244 @@
 
 #include "../locale/localeinfo.h"
 
+/* Track status while looking for sequences in a string.  */
+typedef struct
+{
+  int len;			/* Length of the current sequence.  */
+  int val;			/* Position of the sequence relative to the
+				   previous non-ignored sequence.  */
+  size_t idxnow;		/* Current index in sequences.  */
+  size_t idxmax;		/* Maximum index in sequences.  */
+  size_t idxcnt;		/* Current count of indeces.  */
+  size_t backw;			/* Current Backward sequence index.  */
+  size_t backw_stop;		/* Index where the backward sequences stop.  */
+  const USTRING_TYPE *us;	/* The string.  */
+  int32_t *idxarr;		/* Array to cache weight indeces.  */
+  unsigned char *rulearr;	/* Array to cache rules.  */
+} coll_seq;
+
+/* Get next sequence.  The weight indeces are cached, so we don't need to
+   traverse the string.  */
+static void
+get_next_seq_cached (coll_seq *seq, int nrules, int pass,
+		     const unsigned char *rulesets,
+		     const USTRING_TYPE *weights)
+{
+  int val = seq->val = 0;
+  int len = seq->len;
+  size_t backw_stop = seq->backw_stop;
+  size_t backw = seq->backw;
+  size_t idxcnt = seq->idxcnt;
+  size_t idxmax = seq->idxmax;
+  size_t idxnow = seq->idxnow;
+  unsigned char *rulearr = seq->rulearr;
+  int32_t *idxarr = seq->idxarr;
+
+  while (len == 0)
+    {
+      ++val;
+      if (backw_stop != ~0ul)
+	{
+	  /* The is something pushed.  */
+	  if (backw == backw_stop)
+	    {
+	      /* The last pushed character was handled.  Continue
+		 with forward characters.  */
+	      if (idxcnt < idxmax)
+		{
+		  idxnow = idxcnt;
+		  backw_stop = ~0ul;
+		}
+	      else
+		{
+		  /* Nothing anymore.  The backward sequence
+		     ended with the last sequence in the string.  */
+		  idxnow = ~0ul;
+		  break;
+		}
+	    }
+	  else
+	    idxnow = --backw;
+	}
+      else
+	{
+	  backw_stop = idxcnt;
+
+	  while (idxcnt < idxmax)
+	    {
+	      if ((rulesets[rulearr[idxcnt] * nrules + pass]
+		   & sort_backward) == 0)
+		/* No more backward characters to push.  */
+		break;
+	      ++idxcnt;
+	    }
+
+	  if (backw_stop == idxcnt)
+	    {
+	      /* No sequence at all or just one.  */
+	      if (idxcnt == idxmax)
+		/* Note that seq1len is still zero.  */
+		break;
+
+	      backw_stop = ~0ul;
+	      idxnow = idxcnt++;
+	    }
+	  else
+	    /* We pushed backward sequences.  */
+	    idxnow = backw = idxcnt - 1;
+	}
+      len = weights[idxarr[idxnow]++];
+    }
+
+  /* Update the structure.  */
+  seq->val = val;
+  seq->len = len;
+  seq->backw_stop = backw_stop;
+  seq->backw = backw;
+  seq->idxcnt = idxcnt;
+  seq->idxnow = idxnow;
+}
+
+/* Get next sequence.  Traverse the string as required.  */
+static void
+get_next_seq (coll_seq *seq, int nrules, const unsigned char *rulesets,
+	      const USTRING_TYPE *weights, const int32_t *table,
+	      const USTRING_TYPE *extra, const int32_t *indirect)
+{
+#include WEIGHT_H
+  int val = seq->val = 0;
+  int len = seq->len;
+  size_t backw_stop = seq->backw_stop;
+  size_t backw = seq->backw;
+  size_t idxcnt = seq->idxcnt;
+  size_t idxmax = seq->idxmax;
+  size_t idxnow = seq->idxnow;
+  unsigned char *rulearr = seq->rulearr;
+  int32_t *idxarr = seq->idxarr;
+  const USTRING_TYPE *us = seq->us;
+
+  while (len == 0)
+    {
+      ++val;
+      if (backw_stop != ~0ul)
+	{
+	  /* The is something pushed.  */
+	  if (backw == backw_stop)
+	    {
+	      /* The last pushed character was handled.  Continue
+		 with forward characters.  */
+	      if (idxcnt < idxmax)
+		{
+		  idxnow = idxcnt;
+		  backw_stop = ~0ul;
+		}
+	      else
+		/* Nothing anymore.  The backward sequence ended with
+		   the last sequence in the string.  Note that seq2len
+		   is still zero.  */
+		break;
+	    }
+	  else
+	    idxnow = --backw;
+	}
+      else
+	{
+	  backw_stop = idxmax;
+
+	  while (*us != L('\0'))
+	    {
+	      int32_t tmp = findidx (&us, -1);
+	      rulearr[idxmax] = tmp >> 24;
+	      idxarr[idxmax] = tmp & 0xffffff;
+	      idxcnt = idxmax++;
+
+	      if ((rulesets[rulearr[idxcnt] * nrules]
+		   & sort_backward) == 0)
+		/* No more backward characters to push.  */
+		break;
+	      ++idxcnt;
+	    }
+
+	  if (backw_stop >= idxcnt)
+	    {
+	      /* No sequence at all or just one.  */
+	      if (idxcnt == idxmax || backw_stop > idxcnt)
+		/* Note that seq1len is still zero.  */
+		break;
+
+	      backw_stop = ~0ul;
+	      idxnow = idxcnt;
+	    }
+	  else
+	    /* We pushed backward sequences.  */
+	    idxnow = backw = idxcnt - 1;
+	}
+      len = weights[idxarr[idxnow]++];
+    }
+
+  /* Update the structure.  */
+  seq->val = val;
+  seq->len = len;
+  seq->backw_stop = backw_stop;
+  seq->backw = backw;
+  seq->idxcnt = idxcnt;
+  seq->idxmax = idxmax;
+  seq->idxnow = idxnow;
+  seq->us = us;
+}
+
+/* Compare two sequences.  */
+static int
+do_compare (coll_seq *seq1, coll_seq *seq2, int position,
+	    const USTRING_TYPE *weights)
+{
+  int seq1len = seq1->len;
+  int seq2len = seq2->len;
+  int val1 = seq1->val;
+  int val2 = seq2->val;
+  int32_t *idx1arr = seq1->idxarr;
+  int32_t *idx2arr = seq2->idxarr;
+  int idx1now = seq1->idxnow;
+  int idx2now = seq2->idxnow;
+  int result = 0;
+
+  /* Test for position if necessary.  */
+  if (position && val1 != val2)
+    {
+      result = val1 - val2;
+      goto out;
+    }
+
+  /* Compare the two sequences.  */
+  do
+    {
+      if (weights[idx1arr[idx1now]] != weights[idx2arr[idx2now]])
+	{
+	  /* The sequences differ.  */
+	  result = weights[idx1arr[idx1now]] - weights[idx2arr[idx2now]];
+	  goto out;
+	}
+
+      /* Increment the offsets.  */
+      ++idx1arr[idx1now];
+      ++idx2arr[idx2now];
+
+      --seq1len;
+      --seq2len;
+    }
+  while (seq1len > 0 && seq2len > 0);
+
+  if (position && seq1len != seq2len)
+    result = seq1len - seq2len;
+
+out:
+  seq1->len = seq1len;
+  seq2->len = seq2len;
+  return result;
+}
+
 int
-STRCOLL (s1, s2, l)
-     const STRING_TYPE *s1;
-     const STRING_TYPE *s2;
-     __locale_t l;
+STRCOLL (const STRING_TYPE *s1, const STRING_TYPE *s2, __locale_t l)
 {
   struct __locale_data *current = l->__locales[LC_COLLATE];
   uint_fast32_t nrules = current->values[_NL_ITEM_INDEX (_NL_COLLATE_NRULES)].word;
@@ -56,34 +289,6 @@ STRCOLL (s1, s2, l)
   const USTRING_TYPE *weights;
   const USTRING_TYPE *extra;
   const int32_t *indirect;
-  uint_fast32_t pass;
-  int result = 0;
-  const USTRING_TYPE *us1;
-  const USTRING_TYPE *us2;
-  size_t s1len;
-  size_t s2len;
-  int32_t *idx1arr;
-  int32_t *idx2arr;
-  unsigned char *rule1arr;
-  unsigned char *rule2arr;
-  size_t idx1max;
-  size_t idx2max;
-  size_t idx1cnt;
-  size_t idx2cnt;
-  size_t idx1now;
-  size_t idx2now;
-  size_t backw1_stop;
-  size_t backw2_stop;
-  size_t backw1;
-  size_t backw2;
-  int val1;
-  int val2;
-  int position;
-  int seq1len;
-  int seq2len;
-  int use_malloc;
-
-#include WEIGHT_H
 
   if (nrules == 0)
     return STRCMP (s1, s2);
@@ -98,7 +303,6 @@ STRCOLL (s1, s2, l)
     current->values[_NL_ITEM_INDEX (CONCAT(_NL_COLLATE_EXTRA,SUFFIX))].string;
   indirect = (const int32_t *)
     current->values[_NL_ITEM_INDEX (CONCAT(_NL_COLLATE_INDIRECT,SUFFIX))].string;
-  use_malloc = 0;
 
   assert (((uintptr_t) table) % __alignof__ (table[0]) == 0);
   assert (((uintptr_t) weights) % __alignof__ (weights[0]) == 0);
@@ -106,18 +310,13 @@ STRCOLL (s1, s2, l)
   assert (((uintptr_t) indirect) % __alignof__ (indirect[0]) == 0);
 
   /* We need this a few times.  */
-  s1len = STRLEN (s1);
-  s2len = STRLEN (s2);
+  size_t s1len = STRLEN (s1);
+  size_t s2len = STRLEN (s2);
 
   /* Catch empty strings.  */
-  if (__builtin_expect (s1len == 0, 0) || __builtin_expect (s2len == 0, 0))
+  if (__glibc_unlikely (s1len == 0) || __glibc_unlikely (s2len == 0))
     return (s1len != 0) - (s2len != 0);
 
-  /* We need the elements of the strings as unsigned values since they
-     are used as indeces.  */
-  us1 = (const USTRING_TYPE *) s1;
-  us2 = (const USTRING_TYPE *) s2;
-
   /* Perform the first pass over the string and while doing this find
      and store the weights for each character.  Since we want this to
      be as fast as possible we are using `alloca' to store the temporary
@@ -127,14 +326,27 @@ STRCOLL (s1, s2, l)
 
      Please note that the localedef programs makes sure that `position'
      is not used at the first level.  */
+
+  coll_seq seq1, seq2;
+  bool use_malloc = false;
+  int result = 0;
+
+  memset (&seq1, 0, sizeof (seq1));
+  seq2 = seq1;
+
+  /* We need the elements of the strings as unsigned values since they
+     are used as indeces.  */
+  seq1.us = (const USTRING_TYPE *) s1;
+  seq2.us = (const USTRING_TYPE *) s2;
+
   if (! __libc_use_alloca ((s1len + s2len) * (sizeof (int32_t) + 1)))
     {
-      idx1arr = (int32_t *) malloc ((s1len + s2len) * (sizeof (int32_t) + 1));
-      idx2arr = &idx1arr[s1len];
-      rule1arr = (unsigned char *) &idx2arr[s2len];
-      rule2arr = &rule1arr[s1len];
+      seq1.idxarr = (int32_t *) malloc ((s1len + s2len) * (sizeof (int32_t) + 1));
+      seq2.idxarr = &seq1.idxarr[s1len];
+      seq1.rulearr = (unsigned char *) &seq2.idxarr[s2len];
+      seq2.rulearr = &seq1.rulearr[s1len];
 
-      if (idx1arr == NULL)
+      if (seq1.idxarr == NULL)
 	/* No memory.  Well, go with the stack then.
 
 	   XXX Once this implementation is stable we will handle this
@@ -142,396 +354,73 @@ STRCOLL (s1, s2, l)
 	   do this in time.  This means, though, that this happens for
 	   every pass again.  */
 	goto try_stack;
-      use_malloc = 1;
+      use_malloc = true;
     }
   else
     {
     try_stack:
-      idx1arr = (int32_t *) alloca (s1len * sizeof (int32_t));
-      idx2arr = (int32_t *) alloca (s2len * sizeof (int32_t));
-      rule1arr = (unsigned char *) alloca (s1len);
-      rule2arr = (unsigned char *) alloca (s2len);
+      seq1.idxarr = (int32_t *) alloca (s1len * sizeof (int32_t));
+      seq2.idxarr = (int32_t *) alloca (s2len * sizeof (int32_t));
+      seq1.rulearr = (unsigned char *) alloca (s1len);
+      seq2.rulearr = (unsigned char *) alloca (s2len);
     }
 
-  idx1cnt = 0;
-  idx2cnt = 0;
-  idx1max = 0;
-  idx2max = 0;
-  idx1now = 0;
-  idx2now = 0;
-  backw1_stop = ~0ul;
-  backw2_stop = ~0ul;
-  backw1 = ~0ul;
-  backw2 = ~0ul;
-  seq1len = 0;
-  seq2len = 0;
-  position = rulesets[0] & sort_position;
-  while (1)
-    {
-      val1 = 0;
-      val2 = 0;
-
-      /* Get the next non-IGNOREd element for string `s1'.  */
-      if (seq1len == 0)
-	do
-	  {
-	    ++val1;
-
-	    if (backw1_stop != ~0ul)
-	      {
-		/* The is something pushed.  */
-		if (backw1 == backw1_stop)
-		  {
-		    /* The last pushed character was handled.  Continue
-		       with forward characters.  */
-		    if (idx1cnt < idx1max)
-		      {
-			idx1now = idx1cnt;
-			backw1_stop = ~0ul;
-		      }
-		    else
-		      /* Nothing anymore.  The backward sequence ended with
-			 the last sequence in the string.  Note that seq1len
-			 is still zero.  */
-		      break;
-		  }
-		else
-		  idx1now = --backw1;
-	      }
-	    else
-	      {
-		backw1_stop = idx1max;
-
-		while (*us1 != L('\0'))
-		  {
-		    int32_t tmp = findidx (&us1, -1);
-		    rule1arr[idx1max] = tmp >> 24;
-		    idx1arr[idx1max] = tmp & 0xffffff;
-		    idx1cnt = idx1max++;
-
-		    if ((rulesets[rule1arr[idx1cnt] * nrules]
-			 & sort_backward) == 0)
-		      /* No more backward characters to push.  */
-		      break;
-		    ++idx1cnt;
-		  }
-
-		if (backw1_stop >= idx1cnt)
-		  {
-		    /* No sequence at all or just one.  */
-		    if (idx1cnt == idx1max || backw1_stop > idx1cnt)
-		      /* Note that seq1len is still zero.  */
-		      break;
-
-		    backw1_stop = ~0ul;
-		    idx1now = idx1cnt;
-		  }
-		else
-		  /* We pushed backward sequences.  */
-		  idx1now = backw1 = idx1cnt - 1;
-	      }
-	  }
-	while ((seq1len = weights[idx1arr[idx1now]++]) == 0);
-
-      /* And the same for string `s2'.  */
-      if (seq2len == 0)
-	do
-	  {
-	    ++val2;
-
-	    if (backw2_stop != ~0ul)
-	      {
-		/* The is something pushed.  */
-		if (backw2 == backw2_stop)
-		  {
-		    /* The last pushed character was handled.  Continue
-		       with forward characters.  */
-		    if (idx2cnt < idx2max)
-		      {
-			idx2now = idx2cnt;
-			backw2_stop = ~0ul;
-		      }
-		    else
-		      /* Nothing anymore.  The backward sequence ended with
-			 the last sequence in the string.  Note that seq2len
-			 is still zero.  */
-		      break;
-		  }
-		else
-		  idx2now = --backw2;
-	      }
-	    else
-	      {
-		backw2_stop = idx2max;
-
-		while (*us2 != L('\0'))
-		  {
-		    int32_t tmp = findidx (&us2, -1);
-		    rule2arr[idx2max] = tmp >> 24;
-		    idx2arr[idx2max] = tmp & 0xffffff;
-		    idx2cnt = idx2max++;
-
-		    if ((rulesets[rule2arr[idx2cnt] * nrules]
-			 & sort_backward) == 0)
-		      /* No more backward characters to push.  */
-		      break;
-		    ++idx2cnt;
-		  }
-
-		if (backw2_stop >= idx2cnt)
-		  {
-		    /* No sequence at all or just one.  */
-		    if (idx2cnt == idx2max || backw2_stop > idx2cnt)
-		      /* Note that seq1len is still zero.  */
-		      break;
-
-		    backw2_stop = ~0ul;
-		    idx2now = idx2cnt;
-		  }
-		else
-		  /* We pushed backward sequences.  */
-		  idx2now = backw2 = idx2cnt - 1;
-	      }
-	  }
-	while ((seq2len = weights[idx2arr[idx2now]++]) == 0);
-
-      /* See whether any or both strings are empty.  */
-      if (seq1len == 0 || seq2len == 0)
-	{
-	  if (seq1len == seq2len)
-	    /* Both ended.  So far so good, both strings are equal at the
-	       first level.  */
-	    break;
-
-	  /* This means one string is shorter than the other.  Find out
-	     which one and return an appropriate value.  */
-	  result = seq1len == 0 ? -1 : 1;
-	  goto free_and_return;
-	}
+  seq1.rulearr[0] = 0;
 
-      /* Test for position if necessary.  */
-      if (position && val1 != val2)
-	{
-	  result = val1 - val2;
-	  goto free_and_return;
-	}
-
-      /* Compare the two sequences.  */
-      do
-	{
-	  if (weights[idx1arr[idx1now]] != weights[idx2arr[idx2now]])
-	    {
-	      /* The sequences differ.  */
-	      result = weights[idx1arr[idx1now]] - weights[idx2arr[idx2now]];
-	      goto free_and_return;
-	    }
-
-	  /* Increment the offsets.  */
-	  ++idx1arr[idx1now];
-	  ++idx2arr[idx2now];
-
-	  --seq1len;
-	  --seq2len;
-	}
-      while (seq1len > 0 && seq2len > 0);
-
-      if (position && seq1len != seq2len)
-	{
-	  result = seq1len - seq2len;
-	  goto free_and_return;
-	}
-    }
-
-  /* Now the remaining passes over the weights.  We now use the
-     indeces we found before.  */
-  for (pass = 1; pass < nrules; ++pass)
+  /* Cache values in the first pass and if needed, use them in subsequent
+     passes.  */
+  for (int pass = 0; pass < nrules; ++pass)
     {
+      seq1.idxcnt = 0;
+      seq1.backw_stop = ~0ul;
+      seq1.backw = ~0ul;
+      seq2.idxcnt = 0;
+      seq2.backw_stop = ~0ul;
+      seq2.backw = ~0ul;
+
       /* We assume that if a rule has defined `position' in one section
 	 this is true for all of them.  */
-      idx1cnt = 0;
-      idx2cnt = 0;
-      backw1_stop = ~0ul;
-      backw2_stop = ~0ul;
-      backw1 = ~0ul;
-      backw2 = ~0ul;
-      position = rulesets[rule1arr[0] * nrules + pass] & sort_position;
+      int position = rulesets[seq1.rulearr[0] * nrules + pass] & sort_position;
 
       while (1)
 	{
-	  val1 = 0;
-	  val2 = 0;
-
-	  /* Get the next non-IGNOREd element for string `s1'.  */
-	  if (seq1len == 0)
-	    do
-	      {
-		++val1;
-
-		if (backw1_stop != ~0ul)
-		  {
-		    /* The is something pushed.  */
-		    if (backw1 == backw1_stop)
-		      {
-			/* The last pushed character was handled.  Continue
-			   with forward characters.  */
-			if (idx1cnt < idx1max)
-			  {
-			    idx1now = idx1cnt;
-			    backw1_stop = ~0ul;
-			  }
-			else
-			  {
-			    /* Nothing anymore.  The backward sequence
-			       ended with the last sequence in the string.  */
-			    idx1now = ~0ul;
-			    break;
-			  }
-		      }
-		    else
-		      idx1now = --backw1;
-		  }
-		else
-		  {
-		    backw1_stop = idx1cnt;
-
-		    while (idx1cnt < idx1max)
-		      {
-			if ((rulesets[rule1arr[idx1cnt] * nrules + pass]
-			     & sort_backward) == 0)
-			  /* No more backward characters to push.  */
-			  break;
-			++idx1cnt;
-		      }
-
-		    if (backw1_stop == idx1cnt)
-		      {
-			/* No sequence at all or just one.  */
-			if (idx1cnt == idx1max)
-			  /* Note that seq1len is still zero.  */
-			  break;
-
-			backw1_stop = ~0ul;
-			idx1now = idx1cnt++;
-		      }
-		    else
-		      /* We pushed backward sequences.  */
-		      idx1now = backw1 = idx1cnt - 1;
-		  }
-	      }
-	    while ((seq1len = weights[idx1arr[idx1now]++]) == 0);
-
-	  /* And the same for string `s2'.  */
-	  if (seq2len == 0)
-	    do
-	      {
-		++val2;
-
-		if (backw2_stop != ~0ul)
-		  {
-		    /* The is something pushed.  */
-		    if (backw2 == backw2_stop)
-		      {
-			/* The last pushed character was handled.  Continue
-			   with forward characters.  */
-			if (idx2cnt < idx2max)
-			  {
-			    idx2now = idx2cnt;
-			    backw2_stop = ~0ul;
-			  }
-			else
-			  {
-			    /* Nothing anymore.  The backward sequence
-			       ended with the last sequence in the string.  */
-			    idx2now = ~0ul;
-			    break;
-			  }
-		      }
-		    else
-		      idx2now = --backw2;
-		  }
-		else
-		  {
-		    backw2_stop = idx2cnt;
-
-		    while (idx2cnt < idx2max)
-		      {
-			if ((rulesets[rule2arr[idx2cnt] * nrules + pass]
-			     & sort_backward) == 0)
-			  /* No more backward characters to push.  */
-			  break;
-			++idx2cnt;
-		      }
-
-		    if (backw2_stop == idx2cnt)
-		      {
-			/* No sequence at all or just one.  */
-			if (idx2cnt == idx2max)
-			  /* Note that seq2len is still zero.  */
-			  break;
-
-			backw2_stop = ~0ul;
-			idx2now = idx2cnt++;
-		      }
-		    else
-		      /* We pushed backward sequences.  */
-		      idx2now = backw2 = idx2cnt - 1;
-		  }
-	      }
-	    while ((seq2len = weights[idx2arr[idx2now]++]) == 0);
+	  if (pass == 0)
+	    {
+	      get_next_seq (&seq1, nrules, rulesets, weights, table, extra,
+			    indirect);
+	      get_next_seq (&seq2, nrules, rulesets, weights, table, extra,
+			    indirect);
+	    }
+	  else
+	    {
+	      get_next_seq_cached (&seq1, nrules, pass, rulesets, weights);
+	      get_next_seq_cached (&seq2, nrules, pass, rulesets, weights);
+	    }
 
 	  /* See whether any or both strings are empty.  */
-	  if (seq1len == 0 || seq2len == 0)
+	  if (seq1.len == 0 || seq2.len == 0)
 	    {
-	      if (seq1len == seq2len)
+	      if (seq1.len == seq2.len)
 		/* Both ended.  So far so good, both strings are equal
 		   at this level.  */
 		break;
 
 	      /* This means one string is shorter than the other.  Find out
 		 which one and return an appropriate value.  */
-	      result = seq1len == 0 ? -1 : 1;
+	      result = seq1.len == 0 ? -1 : 1;
 	      goto free_and_return;
 	    }
 
-	  /* Test for position if necessary.  */
-	  if (position && val1 != val2)
-	    {
-	      result = val1 - val2;
-	      goto free_and_return;
-	    }
-
-	  /* Compare the two sequences.  */
-	  do
-	    {
-	      if (weights[idx1arr[idx1now]] != weights[idx2arr[idx2now]])
-		{
-		  /* The sequences differ.  */
-		  result = (weights[idx1arr[idx1now]]
-			    - weights[idx2arr[idx2now]]);
-		  goto free_and_return;
-		}
-
-	      /* Increment the offsets.  */
-	      ++idx1arr[idx1now];
-	      ++idx2arr[idx2now];
-
-	      --seq1len;
-	      --seq2len;
-	    }
-	  while (seq1len > 0 && seq2len > 0);
-
-	  if (position && seq1len != seq2len)
-	    {
-	      result = seq1len - seq2len;
-	      goto free_and_return;
-	    }
+	  result = do_compare (&seq1, &seq2, position, weights);
+	  if (result != 0)
+	    goto free_and_return;
 	}
     }
 
   /* Free the memory if needed.  */
  free_and_return:
   if (use_malloc)
-    free (idx1arr);
+    free (seq1.idxarr);
 
   return result;
 }