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making INT_STRLEN_BOUND tight for unsigned types
From: |
Jim Meyering |
Subject: |
making INT_STRLEN_BOUND tight for unsigned types |
Date: |
Tue, 27 Sep 2005 00:46:36 +0200 |
The fact that INT_STRLEN_BOUND would overestimate for common sizes like
2, 4, and 16-byte unsigned quantities has been a minor annoyance (albeit
more aesthetic/pedantic than practical). Today I saw how to fix it,
but only when compiling with gcc.
Reminder: we can't just use TYPE_SIGNED(t) directly because
that macro casts to type (t), and INT_STRLEN_BOUND's `t'
may be an expression as well as a type.
An unexpected bonus: this change makes the comment,
`Subtract 1 for the sign bit if T is signed;'
obviously true once again.
Any objection?
P.S. The first time I coded this, I did it with two
INT_STRLEN_BOUND definitions, but that definition has
enough grist that I prefer to define a new private macro.
P.P.S: At least two other compilers do support __typeof__,
but I don't think its worth the autoconf test required to
let them use the tighter bound here.
2005-09-27 Jim Meyering <address@hidden>
* intprops.h (signed_type_or_expr__): Define.
(INT_STRLEN_BOUND) [__GNUC__]: Use a slightly tighter bound
for unsigned types.
Index: lib/intprops.h
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/intprops.h,v
retrieving revision 1.6
diff -u -p -r1.6 intprops.h
--- lib/intprops.h 14 May 2005 06:03:58 -0000 1.6
+++ lib/intprops.h 26 Sep 2005 22:42:57 -0000
@@ -53,12 +53,25 @@
? (t) -1 \
: ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+/* Return zero if T can be determined to be an unsigned type.
+ Otherwise, return 1.
+ When compiling with GCC, INT_STRLEN_BOUND uses this macro to obtain a
+ tighter bound. Otherwise, it overestimates the true bound by one byte
+ when applied to unsigned types of size 2, 4, 16, ... bytes.
+ The symbol signed_type_or_expr__ is private to this header file. */
+#if __GNUC__
+# define signed_type_or_expr__(t) TYPE_SIGNED (__typeof__ (t))
+#else
+# define signed_type_or_expr__(t) 1
+#endif
+
/* Bound on length of the string representing an integer type or expression T.
- Subtract 1 for the sign bit if t is signed; log10 (2.0) < 146/485;
+ Subtract 1 for the sign bit if T is signed; log10 (2.0) < 146/485;
add 1 for integer division truncation; add 1 more for a minus sign
if needed. */
#define INT_STRLEN_BOUND(t) \
- ((sizeof (t) * CHAR_BIT - 1) * 146 / 485 + 2)
+ ((sizeof (t) * CHAR_BIT - signed_type_or_expr__ (t)) * 146 / 485 \
+ + signed_type_or_expr__ (t) + 1)
/* Bound on buffer size needed to represent an integer type or expression T,
including the terminating null. */
- making INT_STRLEN_BOUND tight for unsigned types,
Jim Meyering <=