1 files changed, 85 insertions, 0 deletions
diff --git a/vere/pkg/noun/jets/e/rub.c b/vere/pkg/noun/jets/e/rub.c
new file mode 100644
index 0000000..81739be
--- /dev/null
+++ b/vere/pkg/noun/jets/e/rub.c
@@ -0,0 +1,85 @@
+/// @file
+
+#include "jets/q.h"
+#include "jets/w.h"
+
+#include "noun.h"
+
+
+  u3_noun
+  u3qe_rub(u3_atom a,
+           u3_atom b)
+  {
+    u3_atom c, d, e;
+    u3_atom w, x, y, z;
+    u3_atom p, q;
+
+    u3_atom m;
+    {
+      c3_w  bit_w = u3r_met(0, b);
+      u3_noun bit = u3i_words(1, &bit_w);
+      m = u3qa_add(a, bit);
+      u3z(bit);
+    }
+
+    //  Compute c and d.
+    {
+      x = u3k(a);
+
+      while ( 0 == u3qc_cut(0, x, 1, b) ) {
+        u3_atom y = u3qa_inc(x);
+
+        //  Sanity check: crash if decoding more bits than available
+        if ( c3y == u3qa_gth(x, m)) {
+          //  u3l_log("[%%rub-hard %d %d %d]", a, x, m);
+          return u3m_bail(c3__exit);
+        }
+
+        u3z(x);
+        x = y;
+      }
+      if ( c3y == u3r_sing(x, a) ) {
+        u3z(x);
+        return u3nc(1, 0);
+      }
+      c = u3qa_sub(x, a);
+      d = u3qa_inc(x);
+
+      u3z(x);
+    }
+
+    //  Compute e, p, q.
+    {
+      x = u3qa_dec(c);
+      y = u3qc_bex(x);
+      z = u3qc_cut(0, d, x, b);
+
+      e = u3qa_add(y, z);
+      u3z(y); u3z(z);
+
+      w = u3qa_add(c, c);
+      y = u3qa_add(w, e);
+      z = u3qa_add(d, x);
+
+      p = u3qa_add(w, e);
+      q = u3qc_cut(0, z, e, b);
+
+      u3z(w); u3z(x); u3z(y); u3z(z);
+
+      return u3nc(p, q);
+    }
+  }
+  u3_noun
+  u3we_rub(u3_noun cor)
+  {
+    u3_noun a, b;
+
+    if ( (c3n == u3r_mean(cor, u3x_sam_2, &a, u3x_sam_3, &b, 0)) ||
+         (c3n == u3ud(a)) ||
+         (c3n == u3ud(b)) )
+    {
+      return u3m_bail(c3__fail);
+    } else {
+      return u3qe_rub(a, b);
+    }
+  }