comb: bug: missing combinations.

The comb function is broken; some combinations of items
are missing in the output. This is because the iteration
reset step in comb_gen_fun_common handles only one
column of the state, neglecting to reset the other
columns: what is now done by the for (j = i ...
loop.  I'm changing the representation of the state from
a list of lists to a vector of lists. Moreover, it is not
reversed. This allows the loop in comb_gen_fun_common
to perform random access.

* combi.c (k_conses): Return a vector, that is not
reversed.
(comb_init): New helper function to slightly abstract
the use of k_conses.
(comb_while_fun): Termination now occurs if the state
vector is nil (degenerate case, like k items chosen
from n, when k > n), or if the vector has nil in
element zero (special flag situation).
(comb_gen_fun_common): Rewritten, with correction.
The logic is similar. Since we have random access,
we don't need the "prev" variable. When we reset
a column iterator, we now also populate all the
columns to the right of it. For instance, if a
given column resets to (a b c), the one to the right
must reset to (b c), and so on. In the broken function,
this is what was not done, resulting in missing
items due to, say, a column resetting to (a b c)
but the one next to it remaining at (c).
(comb_list_gen_fun): Drop nreverse.
(comb_vec_gen_fun, comb_str_gen_fun, comb_hash_gen_fun):
Use the same i iterator for the state and the output object,
accessing the vector directly.
(comb_list, comb_vec, comb_str, comb_hash): Use comb_init.

* tests/015/comb.tl: New file.

1 files changed, 116 insertions, 0 deletions

diff --git a/tests/015/comb.tl b/tests/015/comb.tl
new file mode 100644
index 00000000..c60b8f2a
--- /dev/null
+++ b/tests/015/comb.tl
@@ -0,0 +1,116 @@
+(load "../common")
+
+(defun normtype (obj)
+  (etypecase obj
+    (null 'list)
+    (cons 'list)
+    (lit 'string)
+    (str 'string)
+    (vec 'vec)))
+
+(defun test-comb (s k)
+  (let ((out (comb s k))
+        (nCk (n-choose-k (len s) k)))
+    (if (> k (len s))
+      (test out nil)
+      (mvtest
+        (len out) nCk
+        (len (uniq out)) nCk))
+    (vtest
+      (sort out) out)
+    (unless (empty out)
+      (let ((stype (normtype s))
+            (otype (normtype (first out))))
+        (vtest stype otype)))))
+
+(test-comb #() 0)
+(test-comb #() 1)
+(test-comb #(1) 0)
+(test-comb #(1) 1)
+(test-comb #(1) 2)
+(test-comb #(1 2) 0)
+(test-comb #(1 2) 1)
+(test-comb #(1 2) 2)
+(test-comb #(1 2) 3)
+(test-comb #(1 2 3) 0)
+(test-comb #(1 2 3) 1)
+(test-comb #(1 2 3) 2)
+(test-comb #(1 2 3) 3)
+(test-comb #(1 2 3) 4)
+(test-comb #(1 2 3 4) 0)
+(test-comb #(1 2 3 4) 1)
+(test-comb #(1 2 3 4) 2)
+(test-comb #(1 2 3 4) 3)
+(test-comb #(1 2 3 4) 4)
+(test-comb #(1 2 3 4) 5)
+(test-comb #(1 2 3 4 5) 0)
+(test-comb #(1 2 3 4 5) 1)
+(test-comb #(1 2 3 4 5) 2)
+(test-comb #(1 2 3 4 5) 3)
+(test-comb #(1 2 3 4 5) 4)
+(test-comb #(1 2 3 4 5) 5)
+(test-comb #(1 2 3 4 5) 5)
+
+(test-comb '() 0)
+(test-comb '() 1)
+(test-comb '(1) 0)
+(test-comb '(1) 1)
+(test-comb '(1) 2)
+(test-comb '(1 2) 0)
+(test-comb '(1 2) 1)
+(test-comb '(1 2) 2)
+(test-comb '(1 2) 3)
+(test-comb '(1 2 3) 0)
+(test-comb '(1 2 3) 1)
+(test-comb '(1 2 3) 2)
+(test-comb '(1 2 3) 3)
+(test-comb '(1 2 3) 4)
+(test-comb '(1 2 3 4) 0)
+(test-comb '(1 2 3 4) 1)
+(test-comb '(1 2 3 4) 2)
+(test-comb '(1 2 3 4) 3)
+(test-comb '(1 2 3 4) 4)
+(test-comb '(1 2 3 4) 5)
+(test-comb '(1 2 3 4 5) 0)
+(test-comb '(1 2 3 4 5) 1)
+(test-comb '(1 2 3 4 5) 2)
+(test-comb '(1 2 3 4 5) 3)
+(test-comb '(1 2 3 4 5) 4)
+(test-comb '(1 2 3 4 5) 5)
+(test-comb '(1 2 3 4 5) 5)
+
+(test-comb "" 0)
+(test-comb "" 1)
+(test-comb "1" 0)
+(test-comb "1" 1)
+(test-comb "1" 2)
+(test-comb "12" 0)
+(test-comb "12" 1)
+(test-comb "12" 2)
+(test-comb "12" 3)
+(test-comb "123" 0)
+(test-comb "123" 1)
+(test-comb "123" 2)
+(test-comb "123" 3)
+(test-comb "123" 4)
+(test-comb "1234" 0)
+(test-comb "1234" 1)
+(test-comb "1234" 2)
+(test-comb "1234" 3)
+(test-comb "1234" 4)
+(test-comb "1234" 5)
+(test-comb "12345" 0)
+(test-comb "12345" 1)
+(test-comb "12345" 2)
+(test-comb "12345" 3)
+(test-comb "12345" 4)
+(test-comb "12345" 5)
+(test-comb "12345" 5)
+
+(mtest
+  (comb #() -1) :error
+  (comb #(1) -1) :error
+  (comb () -1) :error
+  (comb '(1) -1) :error
+  (comb "" -1) :error
+  (comb "a" -1) :error)