Rename $log to $log10.

Verilog-2005 defines the base-10 log function to be $log10. This makes
sense because in C the log() function is the natural log. So add the
$log10 function.

Since there may be legacy code that uses the $log function, leave it
defined, but we should consider at least printing a warning when the
$log function is used.

parse.y

@@ -1206,7 +1206,7 @@ expr_primary
       }
 
   | K_log '(' expression ')'
-      { perm_string tn = perm_string::literal("$log");
+      { perm_string tn = perm_string::literal("$log10");
 	PECallFunction*tmp = make_call_function(tn, $3);
 	FILE_NAME(tmp,@1);
 	$$ = tmp;

vpi/va_math.c

@@ -68,7 +68,12 @@ typedef struct s_single_data {
 static t_single_data va_single_data[]= {
     {"$sqrt",  sqrt},
     {"$ln",    log},
-    {"$log",   log10},
+    {"$log",   log10}, /* FIXME: The $log function is replaced by the
+			  $log10 function to eliminate confusion with
+			  the natural log. In C, "log" is ln and log10
+			  is log-base-10. The $log is being left in for
+			  compatibility. */
+    {"$log10", log10},
     {"$exp",   exp},
     {"$abs",   fabs},
     {"$ceil",  ceil},

vpi/va_math.sft

@@ -7,6 +7,7 @@
 $sqrt   vpiSysFuncReal
 $ln     vpiSysFuncReal
 $log    vpiSysFuncReal
+$log10  vpiSysFuncReal
 $exp    vpiSysFuncReal
 $abs    vpiSysFuncReal
 $ceil   vpiSysFuncReal