1 files changed, 83 insertions, 0 deletions
diff --git a/vere/pkg/noun/jets/d/by_dif.c b/vere/pkg/noun/jets/d/by_dif.c
new file mode 100644
index 0000000..44dcd1a
--- /dev/null
+++ b/vere/pkg/noun/jets/d/by_dif.c
@@ -0,0 +1,83 @@
+/// @file
+
+#include "jets/q.h"
+#include "jets/w.h"
+
+#include "noun.h"
+
+/* internal functions
+*/
+
+/* RETAIN
+*/
+static u3_noun
+_b_dif_join(u3_noun d,
+            u3_noun e)
+{
+  if ( u3_nul == d ) {
+    return u3k(e);
+  }
+  else if ( u3_nul == e ) {
+    return u3k(d);
+  }
+  else {
+    u3_noun n_d, lr_d;
+    u3_noun n_e, lr_e;
+    u3x_cell(d, &n_d, &lr_d);
+    u3x_cell(e, &n_e, &lr_e);
+
+    if ( c3y == u3qc_mor(u3h(n_d), u3h(n_e)) ) {
+      u3_noun l_d, r_d;
+      u3x_cell(lr_d, &l_d, &r_d);
+
+      return u3nt(u3k(n_d),
+                  u3k(l_d),
+                  _b_dif_join(r_d, e));
+    }
+    else {
+      u3_noun l_e, r_e;
+      u3x_cell(lr_e, &l_e, &r_e);
+
+      return u3nt(u3k(n_e),
+                  _b_dif_join(d, l_e),
+                  u3k(r_e));
+    }
+  }
+}
+
+u3_noun
+u3wdb_dif(u3_noun cor)
+{
+  u3_noun a, b;
+  u3x_mean(cor, u3x_sam, &b, u3x_con_sam, &a, 0);
+  return u3qdb_dif(a, b);
+}
+
+u3_noun
+u3qdb_dif(u3_noun a,
+          u3_noun b)
+{
+  if ( u3_nul == b ) {
+    return u3k(a);
+  }
+  else {
+    u3_noun n_b, p_n_b, q_n_b, l_b, r_b;
+    u3_noun c, l_c, r_c;
+    u3x_trel(b, &n_b, &l_b, &r_b);
+    u3x_cell(n_b, &p_n_b, &q_n_b);
+
+    c = u3qdb_bif(a, p_n_b);
+    u3x_cell(c, &l_c, &r_c);
+
+    u3_noun d = u3qdb_dif(l_c, l_b);
+    u3_noun e = u3qdb_dif(r_c, r_b);
+
+    u3z(c);
+
+    u3_noun pro = _b_dif_join(d, e);
+    u3z(d);
+    u3z(e);
+
+    return pro;
+  }
+}