jets: first pass as (scow %da ...)

When trying to hook this up to +scot, I can reliably crash vere,
so there's still a bug here around memory.

pkg/urbit/jets/e/scow.c

@@ -5,6 +5,167 @@
 
 #include <ctype.h>
 
+static
+c3_y to_digit(u3_atom tig)
+{
+  if (tig >= 10) {
+    return 87 + tig;
+  } else {
+    return '0' + tig;
+  }
+}
+
+// gives the characters for a four 'digit' small hex atom.
+static
+void
+_x_co_four(u3_atom src, c3_y* a, c3_y* b, c3_y* c, c3_y* d)
+{
+  *d = to_digit(src & 0xF);
+  src >>= 4;
+  *c = to_digit(src & 0xF);
+  src >>= 4;
+  *b = to_digit(src & 0xF);
+  src >>= 4;
+  *a = to_digit(src & 0xF);
+}
+
+// The parser always prints two digits on 0 in y-co.
+static
+void
+_y_co_two(u3_atom src, c3_y* a, c3_y* b)
+{
+  *b = to_digit(src % 10);
+  *a = to_digit(src / 10);
+}
+
+//
+static
+u3_noun
+_add_year(u3_atom year, u3_noun out)
+{
+  while (year > 0) {
+    out = u3nc(to_digit(year % 10), out);
+    year = year / 10;
+  }
+
+  return out;
+}
+
+static
+u3_noun
+_print_da(u3_atom cor, u3_atom raw_da)
+{
+  u3_noun hok = u3j_cook("u3we_scow_print_da", u3k(cor), "yore");
+  u3_noun yod = u3n_slam_on(hok, u3k(raw_da));
+
+  u3_noun out = 0;
+  u3m_p("yod", yod);
+
+  u3_atom age, year, month, day, hour, min, sec, f;
+  if (c3n == u3r_mean(yod, 4, &age,
+                      5, &year,
+                      6, &month,
+                      14, &day,
+                      30, &hour,
+                      62, &min,
+                      126, &sec,
+                      127, &f,
+                      0)) {
+    return u3m_bail(c3__exit);
+  }
+
+  if (c3n == u3r_sing(f, 0)) {
+    u3_noun f_list = u3qb_flop(f);
+
+    for (u3_noun cur = f_list;
+         _(u3a_is_cell(cur));
+         cur = u3t(cur)) {
+      if (_(u3a_is_cat(u3h(cur)))) {
+        c3_y a, b, c, d;
+        _x_co_four(u3h(cur), &a, &b, &c, &d);
+        out = u3nq('.', a, b, u3nt(c, d, out));
+      } else {
+        // No way to deal with big atoms. fall back.
+        u3z(yod);
+        u3z(out);
+        u3z(f_list);
+        return u3_none;
+      }
+    }
+
+    u3z(f_list);
+    out = u3nc('.', out);
+  }
+
+  // if there isn't a hex list and the h/m/s are all 0, skip printing hours.
+  if (c3n == u3r_sing(f, 0) ||
+      c3n == u3r_sing(hour, 0) ||
+      c3n == u3r_sing(min, 0) ||
+      c3n == u3r_sing(sec, 0)) {
+    if (!_(u3a_is_cat(hour)) ||
+        !_(u3a_is_cat(min)) ||
+        !_(u3a_is_cat(sec))) {
+      // Input is weird, fallback to nock.
+      u3z(yod);
+      u3z(out);
+      return u3_none;
+    }
+
+    c3_y sa, sb, ma, mb, ha, hb;
+    _y_co_two(sec, &sa, &sb);
+    out = u3nq('.', sa, sb, out);
+
+    _y_co_two(min, &ma, &mb);
+    out = u3nq('.', ma, mb, out);
+
+    _y_co_two(hour, &ha, &hb);
+    out = u3nq('.', ha, hb, out);
+
+    out = u3nc('.', out);
+  }
+
+  // We always print the Y.M.D. Unlike others, these numbers are unconstrained
+  // by length, but in practice, the month number and day number can only be up
+  // to two digits because of +yore. We still need to remove 0 prefixes,
+  // though.
+  if (!_(u3a_is_cat(day)) || day > 99 ||
+      !_(u3a_is_cat(month)) || month > 99 ||
+      !_(u3a_is_cat(year))) {
+    // Input is weird, fallback to nock.
+    u3z(yod);
+    u3z(out);
+    return u3_none;
+  }
+
+  c3_y da, db;
+  _y_co_two(day, &da, &db);
+  out = u3nc(db, out);
+  if (da != '0')
+    out = u3nc(da, out);
+  out = u3nc('.', out);
+
+  c3_y ma, mb;
+  _y_co_two(month, &ma, &mb);
+  out = u3nc(mb, out);
+  if (ma != '0')
+    out = u3nc(ma, out);
+  out = u3nc('.', out);
+
+  // suffix the year with a '-' for BC dates
+  if (age == c3n) {
+    out = u3nc('-', out);
+  }
+
+  // The year part is the only place where we have to explicitly loop over the
+  // input because it can be arbitrarily large or small.
+  out = _add_year(year, out);
+
+  out = u3nc('~', out);
+
+  u3z(yod);
+  return out;
+}
+
 static
 u3_noun
 _print_p(u3_atom p)
@@ -83,12 +244,13 @@ u3we_scow(u3_noun cor)
   if (c3n == u3r_mean(cor, u3x_sam_2, &mod,
                       u3x_sam_3, &atom, 0) ||
       !_(u3a_is_cat(mod))) {
+    u3l_log("u3we_scow fail\r\n");
     return u3m_bail(c3__fail);
   }
 
   switch (mod) {
-    /* case c3__da: */
-    /*   return _parse_da(cor, txt); */
+    case c3__da:
+      return _print_da(cor, atom);
 
     case 'p':
       return _print_p(atom);
@@ -115,10 +277,21 @@ u3we_scot(u3_noun cor)
   if (c3n == u3r_mean(cor, u3x_sam_2, &mod,
                       u3x_sam_3, &atom, 0) ||
       !_(u3a_is_cat(mod))) {
+    u3l_log("u3we_scot fail\r\n");
     return u3m_bail(c3__fail);
   }
 
   switch (mod) {
+    // TODO: This causes a bail fail. why?
+    /* case c3__da: { */
+    /*   u3_noun x = _print_da(cor, atom); */
+    /*   if (x == u3_none) { */
+    /*     return x; */
+    /*   } */
+
+    /*   return u3qc_rap(3, x); */
+    /* } */
+
     case 'p':
       return u3qc_rap(3, _print_p(atom));