lib: defend against locale-specific wcstod.

The wcstod function has locale-specific behavior. It uses a
locale-specific decimal separator character, which may not be
the period.  Though in TXR we never call setlocale in order to
activate localization, it is a good idea to put in code to
defend against this. If locale is ever unleashed on the code,
it really botches our floating-point handling. However, let's
keep that defensive logic disabled for now using the
preprocessor.

The strategy is to inquire about the locale's decimal
character at startup. Then, in the flo_str function, we
preprocess the input by converting the decimal period to
the locale-specific character before calling wcstod. On the
output side, we also deal with it in the format function; we
call sprintf, and then convert the locale-specific characer
to period.

I tested all this by temporarily introducing the setlocale
call, and switching to a locale with a comma as the separator,
geting make tests to pass, and doing some interactive testing.
This is not going to receive coverage in the test suite.

* lib.c (dec_point): New global variable.
(flo_str): If dec_point isn't '.', we must copy the
string into a local buffer, which we get from alloca, and
edit any '.' that it contains to dec_point.
(locale_init): New function; initializes dec_point.
(init): Call locale_init.

* lib.h (dec_point): Declared.

* stream.c (formatv): Don't look for a '.' in the result of
printing a double using %e; look for dec_point. Post-process
floating-point sprinf by substituting occurrences of dec_point
with the period.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib.h b/lib.h
index e9c1bd16..3a519905 100644
--- a/lib.h
+++ b/lib.h
@@ -538,6 +538,8 @@ extern val list_f, less_f, greater_f;
 
 extern val prog_string;
 
+extern char dec_point;
+
 #if HAVE_ULONGLONG_T
 typedef ulonglong_t alloc_bytes_t;
 #define SIZEOF_ALLOC_BYTES_T SIZEOF_LONGLONG_T