re PR c++/33067 (Awkward long decimal expansion for double literal in error.)

2011-10-11  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/33067
	* c-family/c-pretty-print.c (pp_c_floating_constant): Output
	max_digits10 (in the ISO C++ WG N1822 sense) decimal digits.

From-SVN: r179797

gcc/ChangeLog

+2011-10-11  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/33067
+	* c-family/c-pretty-print.c (pp_c_floating_constant): Output
+	max_digits10 (in the ISO C++ WG N1822 sense) decimal digits.
+
 2011-10-11  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	* modulo-sched.c: Fix comment typo.  Mention the possibility

gcc/c-family/c-pretty-print.c

@@ -1018,8 +1018,20 @@ pp_c_enumeration_constant (c_pretty_printer *pp, tree e)
 static void
 pp_c_floating_constant (c_pretty_printer *pp, tree r)
 {
+  const struct real_format *fmt
+    = REAL_MODE_FORMAT (TYPE_MODE (TREE_TYPE (r)));
+
+  REAL_VALUE_TYPE floating_cst = TREE_REAL_CST (r);
+  bool is_decimal = floating_cst.decimal;
+
+  /* See ISO C++ WG N1822.  Note: The fraction 643/2136 approximates
+     log10(2) to 7 significant digits.  */
+  int max_digits10 = 2 + (is_decimal ? fmt->p : fmt->p * 643L / 2136);
+
   real_to_decimal (pp_buffer (pp)->digit_buffer, &TREE_REAL_CST (r),
-		   sizeof (pp_buffer (pp)->digit_buffer), 0, 1);
+		   sizeof (pp_buffer (pp)->digit_buffer),
+		   max_digits10, 1);
+
   pp_string (pp, pp_buffer(pp)->digit_buffer);
   if (TREE_TYPE (r) == float_type_node)
     pp_character (pp, 'f');