1 files changed, 229 insertions, 0 deletions
diff --git a/misc/hsearch_r.c b/misc/hsearch_r.c
new file mode 100644
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+/* Copyright (C) 1993, 1995 Free Software Foundation, Inc.
+Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>
+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 Library General Public License as
+published by the Free Software Foundation; either version 2 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+Boston, MA 02111-1307, USA.  */
+
+#include <errno.h>
+#include <malloc.h>
+#include <string.h>
+
+#include <search.h>
+
+/* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
+   [Knuth]            The Art of Computer Programming, part 3 (6.4)  */
+
+
+/* The reentrent version has no static variables to maintain the state.
+   Instead the interface of all functions is extended to take an argument
+   which describes the current status.  */
+typedef struct _ENTRY
+{ 
+  int   used;
+  ENTRY entry;
+}
+_ENTRY;
+
+
+/* For the used double hash method the table size has to be a prime. To
+   correct the user given table size we need a prime test.  This trivial
+   algorithm is adequate because
+   a)  the code is (most probably) called a few times per program run and
+   b)  the number is small because the table must fit in the core  */
+static int
+isprime (number)
+     unsigned int number;
+{
+  /* no even number will be passed */
+  unsigned int div = 3;
+
+  while (div * div < number && number % div != 0)
+    div += 2;
+
+  return number % div != 0;
+}
+
+
+/* Before using the hash table we must allocate memory for it.
+   Test for an existing table are done. We allocate one element
+   more as the found prime number says. This is done for more effective
+   indexing as explained in the comment for the hsearch function.
+   The contents of the table is zeroed, especially the field used 
+   becomes zero.  */
+int
+hcreate_r (nel, htab)
+     unsigned int nel;
+     struct hsearch_data *htab;
+{
+  /* Test for correct arguments.  */
+  if (htab == NULL)
+    {
+      errno = EINVAL;
+      return 0;
+    }
+
+  /* There is still another table active. Return with error. */
+  if (htab->table != NULL)
+    return 0;
+
+  /* Change nel to the first prime number not smaller as nel. */
+  nel |= 1;      /* make odd */
+  while (!isprime (nel))
+    nel += 2;
+
+  htab->size = nel;
+  htab->filled = 0;
+
+  /* allocate memory and zero out */
+  htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY));
+  if (htab->table == NULL)
+    return 0;
+
+  /* everything went alright */
+  return 1;
+}
+
+
+/* After using the hash table it has to be destroyed. The used memory can
+   be freed and the local static variable can be marked as not used.  */
+void
+hdestroy_r (htab)
+     struct hsearch_data *htab;
+{
+  /* Test for correct arguments.  */
+  if (htab == NULL)
+    {
+      errno = EINVAL;
+      return;
+    }
+
+  if (htab->table != NULL)
+    /* free used memory */
+    free (htab->table);
+
+  /* the sign for an existing table is an value != NULL in htable */ 
+  htab->table = NULL;
+}
+
+
+/* This is the search function. It uses double hashing with open adressing.
+   The argument item.key has to be a pointer to an zero terminated, most
+   probably strings of chars. The function for generating a number of the
+   strings is simple but fast. It can be replaced by a more complex function
+   like ajw (see [Aho,Sethi,Ullman]) if the needs are shown.
+  
+   We use an trick to speed up the lookup. The table is created by hcreate
+   with one more element available. This enables us to use the index zero
+   special. This index will never be used because we store the first hash
+   index in the field used where zero means not used. Every other value
+   means used. The used field can be used as a first fast comparison for
+   equality of the stored and the parameter value. This helps to prevent
+   unnecessary expensive calls of strcmp.  */
+int
+hsearch_r (item, action, retval, htab)
+     ENTRY item;
+     ACTION action;
+     ENTRY **retval;
+     struct hsearch_data *htab;
+{
+  unsigned int hval;
+  unsigned int count;
+  unsigned int len = strlen (item.key);
+  unsigned int idx;
+
+  /* If table is full and another entry should be entered return with 
+     error.  */
+  if (action == ENTER && htab->filled == htab->size)
+    {
+      errno = ENOMEM;
+      *retval = NULL;
+      return 0;
+    }
+
+  /* Compute an value for the given string. Perhaps use a better method. */
+  hval = len;
+  count = len;
+  while (count-- > 0)
+    {
+      hval <<= 4;
+      hval += item.key[count];
+    }
+
+  /* First hash function: simply take the modul but prevent zero. */
+  hval %= htab->size;
+  if (hval == 0)
+    ++hval;
+
+  /* The first index tried. */
+  idx = hval;
+
+  if (htab->table[idx].used)
+    {
+      /* Further action might be required according to the action value. */
+      unsigned hval2;
+
+      if (htab->table[idx].used == hval
+	  && strcmp (item.key, htab->table[idx].entry.key) == 0)
+	{
+          if (action == ENTER) 
+	    htab->table[idx].entry.data = item.data;
+
+	  *retval = &htab->table[idx].entry;
+	  return 1;
+	}
+
+      /* Second hash function, as suggested in [Knuth] */
+      hval2 = 1 + hval % (htab->size - 2);
+	
+      do
+	{
+	  /* Because SIZE is prime this guarantees to step through all
+             available indeces.  */
+          if (idx <= hval2)
+	    idx = htab->size + idx - hval2;
+	  else
+	    idx -= hval2;
+
+            /* If entry is found use it. */
+          if (htab->table[idx].used == hval
+	      && strcmp (item.key, htab->table[idx].entry.key) == 0)
+	    {
+              if (action == ENTER) 
+	        htab->table[idx].entry.data = item.data;
+
+	      *retval = &htab->table[idx].entry;
+	      return 1;
+	    }
+	}
+      while (htab->table[idx].used);
+    }
+
+  /* An empty bucket has been found. */
+  if (action == ENTER)
+    {
+      htab->table[idx].used  = hval;
+      htab->table[idx].entry = item;
+
+      ++htab->filled;
+
+      *retval = &htab->table[idx].entry;
+      return 1;
+    }
+
+  errno = ESRCH;
+  *retval = NULL;
+  return 0;
+}