Merge branch 'double-0-check'

changes/double-0-check

@@ -0,0 +1,8 @@
+  o Build improvements (bizarre platform detection):
+    - Try to detect it if we are ever building on a platform where
+      memset(...,0,...) does not set the value of a double to 0.0.  Such
+      platforms are permitted by the C standard, though in practice
+      they're pretty rare (since IEEE 754 is nigh-ubiquitous). We don't
+      currently support them, but it's better to detect them and fail
+      than to perform erroneously.
+

configure.ac

@@ -1033,6 +1033,30 @@ if test "$tor_cv_null_is_zero" != no; then
             [Define to 1 iff memset(0) sets pointers to NULL])
 fi
 
+AC_CACHE_CHECK([whether memset(0) sets doubles to 0.0], tor_cv_dbl0_is_zero,
+[AC_RUN_IFELSE([AC_LANG_SOURCE(
+[[#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#ifdef HAVE_STDDEF_H
+#include <stddef.h>
+#endif
+int main () { double d1,d2; d1=0; memset(&d2,0,sizeof(d2));
+return memcmp(&d1,&d2,sizeof(d1))?1:0; }]])],
+       [tor_cv_dbl0_is_zero=yes],
+       [tor_cv_dbl0_is_zero=no],
+       [tor_cv_dbl0_is_zero=cross])])
+
+if test "$tor_cv_dbl0_is_zero" = cross ; then
+  # Cross-compiling; let's hope that the target isn't raving mad.
+  AC_MSG_NOTICE([Cross-compiling: we'll assume that 0.0 can be represented as a sequence of 0-valued bytes.])
+fi
+
+if test "$tor_cv_dbl0_is_zero" != no; then
+  AC_DEFINE([DOUBLE_0_REP_IS_ZERO_BYTES], 1,
+            [Define to 1 iff memset(0) sets doubles to 0.0])
+fi
+
 # And what happens when we malloc zero?
 AC_CACHE_CHECK([whether we can malloc(0) safely.], tor_cv_malloc_zero_works,
 [AC_RUN_IFELSE([AC_LANG_SOURCE(

src/common/compat.h

@@ -74,6 +74,11 @@
 #error "It seems your platform does not represent NULL as zero. We can't cope."
 #endif
 
+#ifndef DOUBLE_0_REP_IS_ZERO_BYTES
+#error "It seems your platform does not represent 0.0 as zeros. We can't cope."
+#endif
+
+
 #if 'a'!=97 || 'z'!=122 || 'A'!=65 || ' '!=32
 #error "It seems that you encode characters in something other than ASCII."
 #endif

src/win32/orconfig.h

@@ -151,6 +151,9 @@
 /* Define to 1 iff NULL is represented by a 0 in memory. */
 #define NULL_REP_IS_ZERO_BYTES 1
 
+/* Define to 1 iff memset(0) sets doubles to 0.0 */
+#define DOUBLE_0_REP_IS_ZERO_BYTES 1
+
 /* Name of package */
 #define PACKAGE "tor"