diff options
Diffstat (limited to 'src/lisp.h')
| -rw-r--r-- | src/lisp.h | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/src/lisp.h b/src/lisp.h index c5f810a0746..a1bc794ead5 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -765,11 +765,19 @@ extern EMACS_INT string_bytes (struct Lisp_String *); #endif /* not GC_CHECK_STRING_BYTES */ -/* A string cannot contain more bytes than a fixnum can represent, - nor can it be so long that C pointer arithmetic stops working on - the string plus a terminating null. */ -#define STRING_BYTES_MAX \ - min (MOST_POSITIVE_FIXNUM, min (SIZE_MAX, PTRDIFF_MAX) - 1) +/* An upper bound on the number of bytes in a Lisp string, not + counting the terminating null. This a tight enough bound to + prevent integer overflow errors that would otherwise occur during + string size calculations. A string cannot contain more bytes than + a fixnum can represent, nor can it be so long that C pointer + arithmetic stops working on the string plus its terminating null. + Although the actual size limit (see STRING_BYTES_MAX in alloc.c) + may be a bit smaller than STRING_BYTES_BOUND, calculating it here + would expose alloc.c internal details that we'd rather keep + private. The cast to ptrdiff_t ensures that STRING_BYTES_BOUND is + signed. */ +#define STRING_BYTES_BOUND \ + min (MOST_POSITIVE_FIXNUM, (ptrdiff_t) min (SIZE_MAX, PTRDIFF_MAX) - 1) /* Mark STR as a unibyte string. */ #define STRING_SET_UNIBYTE(STR) \ |