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Diffstat (limited to 'configure.in')
| -rw-r--r-- | configure.in | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/configure.in b/configure.in index 26c933b156..e5db37060f 100644 --- a/configure.in +++ b/configure.in @@ -905,6 +905,24 @@ if test "$tor_cv_twos_complement" != no ; then [Define to 1 iff we represent negative integers with two's complement]) fi +# What does shifting a negative value do? +AC_CACHE_CHECK([whether right-shift on negative values does sign-extension], tor_cv_sign_extend, +[AC_RUN_IFELSE([AC_LANG_SOURCE( +[[int main () { int okay = (-60 >> 8) == -1; return okay ? 0 : 1; }]])], + [tor_cv_sign_extend=yes], + [tor_cv_sign_extend=no], + [tor_cv_sign_extend=cross])]) + +if test "$tor_cv_sign_extend" = cross ; then + # Cross-compiling; let's hope that the target isn't raving mad. + AC_MSG_NOTICE([Cross-compiling: we'll assume that right-shifting negative integers causes sign-extension]) +fi + +if test "$tor_cv_sign_extend" != no ; then + AC_DEFINE([RSHIFT_DOES_SIGN_EXTEND], 1, + [Define to 1 iff right-shifting a negative value performs sign-extension]) +fi + # Whether we should use the dmalloc memory allocation debugging library. AC_MSG_CHECKING(whether to use dmalloc (debug memory allocation library)) AC_ARG_WITH(dmalloc, |