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@@ -195,6 +195,21 @@ if test $tor_cv_unaligned_ok = yes; then
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[Define to 1 iff unaligned int access is allowed])
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fi
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+# Now make sure that NULL can be represented as zero bytes.
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+AC_CACHE_CHECK([whether memset(0) sets pointers to NULL], tor_cv_null_is_zero,
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+[AC_RUN_IFELSE([AC_LANG_SOURCE(
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+[[#include <stdlib.h>
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+int main () { char *p1,*p2; p1=NULL; memset(&p2,0,sizeof(p2));
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+return memcmp(&p1,&p2,sizeof(char*)); }]])],
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+ [tor_cv_null_is_zero=yes],
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+ [tor_cv_null_is_zero=no],
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+ [tor_cv_null_is_zero=cross])])
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+
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+if test $tor_cv_null_is_zero = yes; then
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+ AC_DEFINE([NULL_REP_IS_ZERO_BYTES], 1,
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+ [Define to 1 iff memset(0) sets pointers to NULL])
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+fi
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+
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# $prefix stores the value of the --prefix command line option, or
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# NONE if the option wasn't set. In the case that it wasn't set, make
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# it be the default, so that we can use it to expand directories now.
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