Correct some buffer sizes.

- __vfprintf()'s 'buf' has never been used for floating point, so
  don't define it in terms of (incorrect) constants describing
  floating point numbers.  The actual size needed depends on
  sizeof(uintmax_t) and locale details, so I slightly overestimated.

- We don't need a 308-character buffer to store the string "308".
  With long doubles and %a we need more than three characters, though.

1 files changed, 11 insertions, 4 deletions

diff --git a/lib/libc/stdio/floatio.h b/lib/libc/stdio/floatio.h
index a40df00..22fedcd 100644
--- a/lib/libc/stdio/floatio.h
+++ b/lib/libc/stdio/floatio.h
@@ -41,7 +41,14 @@
  * Floating point scanf/printf (input/output) definitions.
  */
 
-/* 11-bit exponent (VAX G floating point) is 308 decimal digits */
-#define	MAXEXP		308
-/* 128 bit fraction takes up 39 decimal digits; max reasonable precision */
-#define	MAXFRACT	39
+/*
+ * MAXEXPDIG is the maximum number of decimal digits needed to store a
+ * floating point exponent in the largest supported format.  It should
+ * be ceil(log10(LDBL_MAX_10_EXP)) or, if hexadecimal floating point
+ * conversions are supported, ceil(log10(LDBL_MAX_EXP)).  But since it
+ * is presently never greater than 5 in practice, we fudge it.
+ */
+#define	MAXEXPDIG	6
+#if LDBL_MAX_EXP > 999999
+#error "floating point buffers too small"
+#endif