Add a macro of an upper bound on the formatted length of an integer

There are lots of places where Puzzles formats integers into
fixed-length buffers using sprintf() with a "%d" format.  This isn't
very safe, since C doesn't guarantee any particular maximum size for an
"int".  However, the restrictions on representations of integers means
we can infer an upper bound using sizeof(), CHAR_BIT, and an
approximation to the binary log of 10.

1 files changed, 3 insertions, 0 deletions

diff --git a/puzzles.h b/puzzles.h
index cbe7f88..2f49613 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -18,6 +18,9 @@
 #define STR_INT(x) #x
 #define STR(x) STR_INT(x)
 
+/* An upper bound on the length of sprintf'ed integers (signed or unsigned). */
+#define MAX_DIGITS(x) (sizeof(x) * CHAR_BIT / 3 + 2)
+
 /* NB not perfect because they evaluate arguments multiple times. */
 #ifndef max
 #define max(x,y) ( (x)>(y) ? (x) : (y) )