+#ifdef GC_CHECK_STRING_BYTES
+
+static int check_string_bytes_count;
+
+void check_string_bytes P_ ((int));
+void check_sblock P_ ((struct sblock *));
+
+#define CHECK_STRING_BYTES(S) STRING_BYTES (S)
+
+
+/* Like GC_STRING_BYTES, but with debugging check. */
+
+int
+string_bytes (s)
+ struct Lisp_String *s;
+{
+ int nbytes = (s->size_byte < 0 ? s->size : s->size_byte) & ~MARKBIT;
+ if (!PURE_POINTER_P (s)
+ && s->data
+ && nbytes != SDATA_NBYTES (SDATA_OF_STRING (s)))
+ abort ();
+ return nbytes;
+}
+
+/* Check validity Lisp strings' string_bytes member in B. */
+
+void
+check_sblock (b)
+ struct sblock *b;
+{
+ struct sdata *from, *end, *from_end;
+
+ end = b->next_free;
+
+ for (from = &b->first_data; from < end; from = from_end)
+ {
+ /* Compute the next FROM here because copying below may
+ overwrite data we need to compute it. */
+ int nbytes;
+
+ /* Check that the string size recorded in the string is the
+ same as the one recorded in the sdata structure. */
+ if (from->string)
+ CHECK_STRING_BYTES (from->string);
+
+ if (from->string)
+ nbytes = GC_STRING_BYTES (from->string);
+ else
+ nbytes = SDATA_NBYTES (from);
+
+ nbytes = SDATA_SIZE (nbytes);
+ from_end = (struct sdata *) ((char *) from + nbytes);
+ }
+}
+
+
+/* Check validity of Lisp strings' string_bytes member. ALL_P
+ non-zero means check all strings, otherwise check only most
+ recently allocated strings. Used for hunting a bug. */
+
+void
+check_string_bytes (all_p)
+ int all_p;
+{
+ if (all_p)
+ {
+ struct sblock *b;
+
+ for (b = large_sblocks; b; b = b->next)
+ {
+ struct Lisp_String *s = b->first_data.string;
+ if (s)
+ CHECK_STRING_BYTES (s);
+ }
+
+ for (b = oldest_sblock; b; b = b->next)
+ check_sblock (b);
+ }
+ else
+ check_sblock (current_sblock);
+}
+
+#endif /* GC_CHECK_STRING_BYTES */
+
+