string-extend: don't use set macro to update length.

* lib.c (string_extend): We know that num_fast + delta is in
the fixnum range, because we checked this condition. So
we can just assign it without informing the garbage collector.
This yields about a 16% speedup in get-csv.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index e23c2ad3..d0667a57 100644
--- a/lib.c
+++ b/lib.c
@@ -5423,7 +5423,7 @@ val string_extend(val str, val tail, val finish_in)
       }
     }
 
-    set(mkloc(str->st.len, str), num(len + delta));
+    str->st.len = num_fast(len + delta);
 
     if (stringp(tail)) {
       wmemcpy(str->st.str + len, c_str(tail, self), delta + 1);