sub-vec: optimize no-op case.

* lib.c (sub_vec): If range covers entire vector, just
return it.

* txr.1: Clarify that the output of sub may share structure
with the input regardless of type, not only when the input
is a list. This should have been updated when the optimizatin
was done in sub-str.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 45e5b865..c462a238 100644
--- a/lib.c
+++ b/lib.c
@@ -7144,6 +7144,8 @@ val sub_vec(val vec_in, val from, val to)
 
   if (ge(from, to)) {
     return vector(zero, nil);
+  } else if (from == zero && eql(to, len)) {
+    return vec_in;
   } else {
     cnum cfrom = c_num(from);
     size_t nelem = c_num(to) - cfrom;