Portability: Use stack-allocated arrays only if the compiler supports them.

5 files changed, 61 insertions, 6 deletions

diff --git a/ChangeLog b/ChangeLog
index ab7c47d..a74b52a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2002-12-12  Bruno Haible  <bruno@clisp.org>
 
+	* src/configure.in: Add test for stack-allocated variable-size arrays.
+	* src/config.h.in: Regenerated.
+	* src/search.cc: Include config.h.
+	(DYNAMIC_ARRAY, FREE_DYNAMIC_ARRAY): New macros.
+	(Search::find_alpha_inc, Search::count_possible_collisions,
+	Search::find_asso_values): Use them.
+	* src/Makefile.in (search.o): Depend on config.h.
+
 	* src/search.h (Search::keyword_list_length, Search::max_key_length,
 	Search::get_max_keysig_size, Search::prepare): Remove declarations.
 	(Search::prepare): Renamed from Search::preprepare.
diff --git a/src/Makefile.in b/src/Makefile.in
index 8774371..fd6d872 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -111,7 +111,7 @@ bool-array.o : bool-array.cc $(BOOL_ARRAY_H) $(OPTIONS_H)
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $(srcdir)/bool-array.cc
 hash-table.o : hash-table.cc $(HASH_TABLE_H) $(OPTIONS_H)
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $(srcdir)/hash-table.cc
-search.o : search.cc $(SEARCH_H) $(OPTIONS_H) $(HASH_TABLE_H)
+search.o : search.cc $(SEARCH_H) $(OPTIONS_H) $(HASH_TABLE_H) $(CONFIG_H)
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $(srcdir)/search.cc
 output.o : output.cc $(OUTPUT_H) $(OPTIONS_H) $(VERSION_H)
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $(srcdir)/output.cc
diff --git a/src/config.h.in b/src/config.h.in
index 4d3d762..3b55444 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -1,5 +1,9 @@
 /* config.h.in.  Generated automatically from configure.in by autoheader.  */
 
+/* Define if the C++ compiler supports stack-allocated variable-size arrays.
+   */
+#undef HAVE_DYNAMIC_ARRAY
+
 /* Define if the C++ compiler supports "throw ()" declarations.  */
 #undef HAVE_THROW_DECL
 
diff --git a/src/configure.in b/src/configure.in
index b80d48e..3a42d13 100644
--- a/src/configure.in
+++ b/src/configure.in
@@ -40,6 +40,19 @@ CL_PROG_INSTALL
 dnl
 dnl           checks for compiler characteristics
 dnl
+AC_MSG_CHECKING([for stack-allocated variable-size arrays])
+AC_CACHE_VAL(gp_cv_cxx_dynamic_array, [
+AC_LANG_SAVE()
+AC_LANG_CPLUSPLUS()
+AC_TRY_COMPILE([int func (int n) { int dynamic_array[n]; }], [],
+gp_cv_cxx_dynamic_array=yes, gp_cv_cxx_dynamic_array=no)
+AC_LANG_RESTORE()
+])
+AC_MSG_RESULT($gp_cv_cxx_dynamic_array)
+if test $gp_cv_cxx_dynamic_array = yes; then
+  AC_DEFINE(HAVE_DYNAMIC_ARRAY, 1,
+    [Define if the C++ compiler supports stack-allocated variable-size arrays.])
+fi
 dnl
 dnl           checks for functions and declarations
 dnl
diff --git a/src/search.cc b/src/search.cc
index 04608c1..a1e3d70 100644
--- a/src/search.cc
+++ b/src/search.cc
@@ -31,9 +31,33 @@
 #include <limits.h> /* defines INT_MIN, INT_MAX, UINT_MAX */
 #include "options.h"
 #include "hash-table.h"
+#include "config.h"
+
+/* ============================== Portability ============================== */
+
 /* Assume ISO C++ 'for' scoping rule.  */
 #define for if (0) ; else for
 
+/* Dynamically allocated array with dynamic extent:
+
+   Example:
+       DYNAMIC_ARRAY (my_array, int, n);
+       ...
+       FREE_DYNAMIC_ARRAY (my_array);
+
+   Attention: depending on your implementation my_array is either the array
+   itself or a pointer to the array! Always use my_array only as expression!
+ */
+#if HAVE_DYNAMIC_ARRAY
+  #define DYNAMIC_ARRAY(var,eltype,size) eltype var[size]
+  #define FREE_DYNAMIC_ARRAY(var)
+#else
+  #define DYNAMIC_ARRAY(var,eltype,size) eltype *var = new eltype[size]
+  #define FREE_DYNAMIC_ARRAY(var) delete[] var
+#endif
+
+/* ================================ Theory ================================= */
+
 /* The most general form of the hash function is
 
       hash (keyword) = sum (asso_values[keyword[i] + alpha_inc[i]] : i in Pos)
@@ -589,7 +613,7 @@ Search::find_alpha_inc ()
           }
       }
 
-      unsigned int indices[nindices];
+      DYNAMIC_ARRAY (indices, unsigned int, nindices);
       {
         unsigned int j = 0;
         PositionIterator iter = _key_positions.iterator(_max_key_len);
@@ -608,8 +632,8 @@ Search::find_alpha_inc ()
       /* Perform several rounds of searching for a good alpha increment.
          Each round reduces the number of artificial collisions by adding
          an increment in a single key position.  */
-      unsigned int best[_max_key_len];
-      unsigned int tryal[_max_key_len];
+      DYNAMIC_ARRAY (best, unsigned int, _max_key_len);
+      DYNAMIC_ARRAY (tryal, unsigned int, _max_key_len);
       do
         {
           /* An increment of 1 is not always enough.  Try higher increments
@@ -644,6 +668,8 @@ Search::find_alpha_inc ()
             }
         }
       while (current_duplicates_count > duplicates_goal);
+      FREE_DYNAMIC_ARRAY (tryal);
+      FREE_DYNAMIC_ARRAY (best);
 
       if (option[DEBUG])
         {
@@ -661,6 +687,7 @@ Search::find_alpha_inc ()
               }
           fprintf (stderr, "\n");
         }
+      FREE_DYNAMIC_ARRAY (indices);
     }
 
   _alpha_inc = current;
@@ -1003,7 +1030,7 @@ Search::count_possible_collisions (EquivalenceClass *partition, unsigned int c)
      Return the sum of this expression over all equivalence classes.  */
   unsigned int sum = 0;
   unsigned int m = _max_selchars_length;
-  unsigned int split_cardinalities[m+1];
+  DYNAMIC_ARRAY (split_cardinalities, unsigned int, m + 1);
   for (EquivalenceClass *cls = partition; cls; cls = cls->_next)
     {
       for (unsigned int i = 0; i <= m; i++)
@@ -1025,6 +1052,7 @@ Search::count_possible_collisions (EquivalenceClass *partition, unsigned int c)
       for (unsigned int i = 0; i <= m; i++)
         sum -= split_cardinalities[i] * split_cardinalities[i];
     }
+  FREE_DYNAMIC_ARRAY (split_cardinalities);
   return sum;
 }
 
@@ -1231,7 +1259,7 @@ Search::find_asso_values ()
         }
 
       unsigned int iterations = 0;
-      unsigned int iter[k];
+      DYNAMIC_ARRAY (iter, unsigned int, k);
       for (unsigned int i = 0; i < k; i++)
         iter[i] = 0;
       unsigned int ii = (_jump != 0 ? k - 1 : 0);
@@ -1384,6 +1412,8 @@ Search::find_asso_values ()
                 ii = 0;
             }
         }
+      FREE_DYNAMIC_ARRAY (iter);
+
       if (option[DEBUG])
         {
           fprintf (stderr, "Step %u chose _asso_values[", stepno);