X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/mLib/blobdiff_plain/412206fddb90693452fe0329689b93b0b23eb4e2..2ae5376b8a8158f38cbbe9c0238b5428ee3ce711:/sym.h

diff --git a/sym.h b/sym.h
index d9d270c..db49ff5 100644
--- a/sym.h
+++ b/sym.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: sym.h,v 1.11 2000/06/17 10:37:39 mdw Exp $
+ * $Id: sym.h,v 1.12 2001/01/20 11:49:37 mdw Exp $
  *
  * Symbol table management
  *
@@ -30,6 +30,12 @@
 /*----- Revision history --------------------------------------------------*
  *
  * $Log: sym.h,v $
+ * Revision 1.12  2001/01/20 11:49:37  mdw
+ * Export tuning parameters from header file, for the benefit of other
+ * hashtable implementations.  Change the storage of symbol names: store
+ * the name after the allocated symbol block in all cases.  This replaces
+ * the previous complicated and slightly wasteful arrangement.
+ *
  * Revision 1.11  2000/06/17 10:37:39  mdw
  * Add support for arena management.
  *
@@ -89,6 +95,27 @@
 #  include "sub.h"
 #endif
 
+/*----- Tuning parameters -------------------------------------------------*/
+
+/* --- Initial hash table size --- *
+ *
+ * This is the initial @mask@ value.  It must be of the form %$2^n - 1$%,
+ * so that it can be used to mask of the bottom bits of a hash value.
+ */
+
+#define SYM_INITSZ 32			/* Size of a new hash table */
+
+/* --- Maximum load factor --- *
+ *
+ * This parameter controls how much the table has to be loaded before the
+ * table is extended.  The number of elements %$n$%, the number of bins %$b$%
+ * and the limit %$l$% satisfy the relation %$n < bl$%; if a new item is
+ * added to the table and this relation is found to be false, the table is
+ * doubled in size.
+ */
+
+#define SYM_LIMIT(n) ((n) * 2)		/* Load factor for growing table */
+
 /*----- Type definitions --------------------------------------------------*/
 
 /* --- Symbol table --- *
@@ -113,23 +140,21 @@ typedef struct sym_table {
  * sufficient to allow me to manipulate such objects.
  */
 
-#define SYM_BUFSZ 16			/* Size of local string buffer */
-
 typedef struct sym_base {
-  hash_base b;
-  union {
-    char *p;				/* Pointer to name string */
-    char b[SYM_BUFSZ];			/* Buffer containing a short name */
-  } name;				/* Name of this symbol */
+  hash_base b;				/* Base structure */
+  char *name;				/* Pointer to name string */
   size_t len;				/* Length of the symbol's name */
 } sym_base;
 
-/* --- A macro to pick a symbol's name out from the mess --- */
+/* --- Macros for picking out useful information --- *
+ *
+ * Note that @SYM_LEN@ returns the size of the symbol key.  For textual keys,
+ * this will include the terminating null.
+ */
 
-#define SYM_NAME(sy)							\
-  (((sym_base *)(sy))->len > SYM_BUFSZ ?				\
-   ((sym_base *)(sy))->name.p :						\
-   ((sym_base *)(sy))->name.b)
+#define SYM_NAME(sy) ((const char *)(((sym_base *)(sy))->name))
+#define SYM_LEN(sy) (((sym_base *)(sy))->len + 0)
+#define SYM_HASH(sy) (((sym_base *)(sy))->b.hash + 0)
 
 /* --- An iterator block --- */