+For example, strtod and mktime have some bugs on some platforms.
+You can work around some of these problems by requiring the relevant
+modules, e.g., the Gnulib 'mktime' module supplies a working and
+conforming 'mktime'.
+
+The GNU coding standards allow one departure from strict C99: Gnulib
+code can assume that standard internal types like size_t are no wider
+than 'long'. POSIX 1003.1-2001 and the GNU coding standards both
+require 'int' to be at least 32 bits wide, so Gnulib code assumes this
+as well. Gnulib code makes the following additional assumptions:
+
+ * Signed integer arithmetic is two's complement.
+
+ Previously, gnulib code sometimes assumed that signed integer
+ arithmetic wraps around, but modern compiler optimizations
+ sometimes do not guarantee this, and gnulib code with this
+ assumption is now considered to be questionable. For more, please
+ see the file doc/intprops.texi.
+
+ Some gnulib modules contain explicit support for the other signed
+ integer representations allowed by C99 (ones' complement and signed
+ magnitude), but these modules are the exception rather than the rule.
+ All practical gnulib targets use two's complement.
+
+ * There are no "holes" in integer values: all the bits of an integer
+ contribute to its value in the usual way.
+
+ * If two nonoverlapping objects have sizes S and T represented as
+ size_t values, then S + T cannot overflow. This assumption is true
+ for all practical hosts with flat address spaces, but it is not
+ always true for hosts with segmented address spaces.
+
+ * If an existing object has size S, and if T is sufficiently small
+ (e.g., 8 KiB), then S + T cannot overflow. Overflow in this case
+ would mean that the rest of your program fits into T bytes, which
+ can't happen in realistic flat-address-space hosts.
+
+ * Objects with all bits zero are treated as 0 or NULL. For example,
+ memset (A, 0, sizeof A) initializes an array A of pointers to NULL.
+
+ * Adding zero to a null pointer does not change the pointer.
+ For example, 0 + (char *) NULL == (char *) NULL.
+
+The above assumptions are not required by the C or POSIX standards but
+hold on all practical porting targets that we're familiar with. If
+you have a porting target where these assumptions are not true, we'd
+appreciate hearing of any fixes. We need fixes that do not increase
+runtime overhead on standard hosts and that are relatively easy to
+maintain.
+
+With the above caveats, Gnulib code should port without problem to new
+hosts, e.g., hosts conforming to C99 or to recent POSIX standards.
+Hence Gnulib code should avoid using constructs (e.g., undeclared
+functions return 'int') that do not conform to C99.