1 files changed, 90 insertions, 0 deletions
diff --git a/vere/pkg/noun/jets/e/fein_ob.c b/vere/pkg/noun/jets/e/fein_ob.c
new file mode 100644
index 0000000..65d0f3a
--- /dev/null
+++ b/vere/pkg/noun/jets/e/fein_ob.c
@@ -0,0 +1,90 @@
+/// @file
+
+#include "jets/q.h"
+#include "jets/w.h"
+
+#include "noun.h"
+#include "murmur3.h"
+
+//  +feis:ob constant parameters to +fe:ob
+//
+static const c3_w a_w =     0xffff;
+static const c3_w b_w =    0x10000;
+static const c3_w k_w = 0xffff0000;
+
+//  +raku:ob
+//
+static const c3_w rak_w[4] = { 0xb76d5eed, 0xee281300, 0x85bcae01, 0x4b387af7 };
+
+/* _fe_ob(): +fe:ob, with constant parameters factored out.
+**           correct over the domain [0x0, 0xfffe.ffff]
+*/
+static c3_w
+_fe_ob(c3_w m_w)
+{
+  c3_w l_w = m_w % a_w;
+  c3_w r_w = m_w / a_w;
+  c3_w f_w, t_w;
+  c3_y j_y, k_y[2];
+
+  for ( j_y = 0; j_y < 4; j_y++ ) {
+    k_y[0] = r_w & 0xff;
+    k_y[1] = (r_w >> 8) & 0xff;
+
+    MurmurHash3_x86_32(k_y, 2, rak_w[j_y], &f_w);
+
+    //  NB: this addition can overflow a c3_w (before mod)
+    //
+    t_w = ((c3_d)f_w + l_w) % (!(j_y & 1) ? a_w : b_w);
+    l_w = r_w;
+    r_w = t_w;
+  }
+
+  //  legendary @max19
+  //
+  return ( a_w == r_w )
+         ? (r_w * a_w) + l_w
+         : (l_w * a_w) + r_w;
+}
+
+/* _feis_ob(): +feis:ob, also offsetting by 0x1.000 (as in +fein:ob).
+**             correct over the domain [0x1.0000, 0xffff.ffff]
+*/
+static c3_w
+_feis_ob(c3_w m_w)
+{
+  c3_w c_w = _fe_ob(m_w - b_w);
+  return b_w + (( c_w < k_w ) ? c_w : _fe_ob(c_w));
+}
+
+u3_atom
+u3qe_fein_ob(u3_atom pyn)
+{
+  c3_w sor_w = u3r_met(4, pyn);
+
+  if ( (sor_w < 2) || (sor_w > 4) ) {
+    return u3k(pyn);
+  }
+
+  if ( 2 == sor_w ) {
+    return u3i_word(_feis_ob(u3r_word(0, pyn)));
+  }
+  else {
+    c3_w pyn_w[2];
+    u3r_words(0, 2, pyn_w, pyn);
+
+    if ( pyn_w[0] < b_w ) {
+      return u3k(pyn);
+    }
+    else {
+      pyn_w[0] = _feis_ob(pyn_w[0]);
+      return u3i_words(2, pyn_w);
+    }
+  }
+}
+
+u3_noun
+u3we_fein_ob(u3_noun cor)
+{
+  return u3qe_fein_ob(u3x_atom(u3x_at(u3x_sam, cor)));
+}