Propagating gettext into gnulib a bit better.

[gnulib.git] / lib / xalloc.h

diff --git a/lib/xalloc.h b/lib/xalloc.h
index 5ccea22..4b65858 100644 (file)
--- a/lib/xalloc.h
+++ b/lib/xalloc.h
@@ -62,8 +62,17 @@ char *xstrdup (const char *str);
 /* Return 1 if an array of N objects, each of size S, cannot exist due
    to size arithmetic overflow.  S must be positive and N must be
    nonnegative.  This is a macro, not an inline function, so that it
-   works correctly even when SIZE_MAX < N.  */
-#define xalloc_oversized(n, s) ((size_t) -1 / (s) < (n))
+   works correctly even when SIZE_MAX < N.
+
+   By gnulib convention, SIZE_MAX represents overflow in size
+   calculations, so the conservative dividend to use here is
+   SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
+   However, malloc (SIZE_MAX) fails on all known hosts where
+   sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for
+   exactly-SIZE_MAX allocations on such hosts; this avoids a test and
+   branch when S is known to be 1.  */
+# define xalloc_oversized(n, s) \
+    ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
 
 /* These macros are deprecated; they will go away soon, and are retained
    temporarily only to ease conversion to the functions described above.  */