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, 32 insertions, 2 deletions

diff --git a/lib.c b/lib.c
index f6c57552..338ff9fc 100644
--- a/lib.c
+++ b/lib.c
@@ -37,6 +37,7 @@
 #include <math.h>
 #include <signal.h>
 #include <assert.h>
+#include <locale.h>
 #include "config.h"
 #include "alloca.h"
 #if HAVE_GETENVIRONMENTSTRINGS
@@ -130,6 +131,10 @@ val list_f, less_f, greater_f;
 
 val prog_string;
 
+#if CONFIG_LOCALE_TOLERANCE
+char dec_point = '.';
+#endif
+
 static val recycled_conses;
 
 const seq_kind_t seq_kind_tab[MAXTYPE+1] = {
@@ -5402,9 +5407,21 @@ val flo_str(val str)
 {
   const wchar_t *wcs = c_str(str);
   wchar_t *ptr;
+  double value;
+
+#if CONFIG_LOCALE_TOLERANCE
+  if (dec_point != '.') {
+    size_t size = c_unum(length_str(str), lit("flot-str")) + 1;
+    wchar_t *wcopy = alloca(sizeof *wcopy * size), *dot = wcopy;
+    wmemcpy(wcopy, wcs, size);
+    wcs = wcopy;
+    while ((dot = wcschr(dot, '.')) != 0)
+      *dot++ = dec_point;
+  }
+#endif
+
+  value = wcstod(wcs, &ptr);
 
-  /* TODO: detect if we have wcstod */
-  double value = wcstod(wcs, &ptr);
   if (value == 0 && ptr == wcs)
     return nil;
   if ((value == HUGE_VAL || value == -HUGE_VAL) && errno == ERANGE)
@@ -11888,6 +11905,16 @@ val in_range_star(val range, val num)
   }
 }
 
+#if CONFIG_LOCALE_TOLERANCE
+
+static void locale_init(void)
+{
+  struct lconv *lc = localeconv();
+  dec_point = *lc->decimal_point;
+}
+
+#endif
+
 static void obj_init(void)
 {
   /*
@@ -12970,6 +12997,9 @@ void init(val *stack_bottom)
 
   t = one;
   gc_init(stack_bottom);
+#if CONFIG_LOCALE_TOLERANCE
+  locale_init();
+#endif
   obj_init();
   uw_init();
   eval_init();