diff --git a/pkg/urbit/jets/e/fein_ob.c b/pkg/urbit/jets/e/fein_ob.c
index fd9333126c..80e1135120 100644
--- a/pkg/urbit/jets/e/fein_ob.c
+++ b/pkg/urbit/jets/e/fein_ob.c
@@ -14,15 +14,16 @@ static const c3_w k_w = 0xffff0000;
 //
 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
-_feis_fe(c3_w m_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, tmp_w;
-  c3_d tmp_d;
-  c3_y k_y[2];
-  c3_y j_y;
+  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;
@@ -30,20 +31,28 @@ _feis_fe(c3_w m_w)
 
     MurmurHash3_x86_32(k_y, 2, rak_w[j_y], &f_w);
 
-    tmp_d = (c3_d)f_w + l_w;
-    tmp_w = tmp_d % (!(j_y & 1) ? a_w: b_w);
-    l_w   = r_w;
-    r_w   = tmp_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;
   }
 
-  return ( a_w == r_w ) ? (r_w * a_w) + l_w : (l_w * a_w) + r_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(c3_w m_w)
+_feis_ob(c3_w m_w)
 {
-  c3_w c_w = _feis_fe(m_w);
-  return ( c_w < k_w ) ? c_w : _feis_fe(c_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
@@ -56,10 +65,7 @@ u3qe_fein_ob(u3_atom pyn)
   }
 
   if ( 2 == sor_w ) {
-    c3_w pyn_w = u3r_word(0, pyn);
-    c3_w out_w = b_w + _feis(pyn_w - b_w);
-
-    return u3i_word(out_w);
+    return u3i_word(_feis_ob(u3r_word(0, pyn)));
   }
   else {
     c3_w pyn_w[2];
@@ -69,7 +75,7 @@ u3qe_fein_ob(u3_atom pyn)
       return u3k(pyn);
     }
     else {
-      pyn_w[0] = b_w + _feis(pyn_w[0] - b_w);
+      pyn_w[0] = _feis_ob(pyn_w[0]);
       return u3i_words(2, pyn_w);
     }
   }
diff --git a/pkg/urbit/jets/e/fynd_ob.c b/pkg/urbit/jets/e/fynd_ob.c
index f32ca1a74f..203d94f4d7 100644
--- a/pkg/urbit/jets/e/fynd_ob.c
+++ b/pkg/urbit/jets/e/fynd_ob.c
@@ -10,46 +10,53 @@ static const c3_w a_w =     0xffff;
 static const c3_w b_w =    0x10000;
 static const c3_w k_w = 0xffff0000;
 
-//  +raku:ob
+//  (flop raku:ob)
 //
-static const c3_w rak_w[4] = { 0xb76d5eed, 0xee281300, 0x85bcae01, 0x4b387af7 };
+static const c3_w kar_w[4] = { 0x4b387af7, 0x85bcae01, 0xee281300, 0xb76d5eed };
 
+/* _fen_ob(): +fen:ob, with constant parameters factored out.
+**           correct over the domain [0x0 ... 0xfffe.ffff]
+*/
 static c3_w
-_tail_fen(c3_w m_w)
+_fen_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, tmp_w;
-  c3_y k_y[2];
-  c3_y j_y;
+  c3_w f_w, t_w;
+  c3_y j_y, k_y[2];
 
+  //  legendary @max19
+  //
   if ( a_w == l_w ) {
-    tmp_w = l_w;
+    t_w = l_w;
     l_w = r_w;
-    r_w = tmp_w;
+    r_w = t_w;
   }
 
-  for ( j_y = 4; j_y > 0; j_y-- ) {
+  for ( j_y = 0; j_y < 4; j_y++ ) {
     k_y[0] = l_w & 0xff;
     k_y[1] = (l_w >> 8) & 0xff;
 
-    MurmurHash3_x86_32(k_y, 2, rak_w[j_y - 1], &f_w);
+    MurmurHash3_x86_32(k_y, 2, kar_w[j_y], &f_w);
 
-    tmp_w = ( j_y & 1 )
-            ? ((r_w + a_w) - (f_w % a_w)) % a_w
-            : ((r_w + b_w) - (f_w % b_w)) % b_w;
+    t_w = ( j_y & 1 )
+          ? ((r_w + a_w) - (f_w % a_w)) % a_w
+          : ((r_w + b_w) - (f_w % b_w)) % b_w;
     r_w = l_w;
-    l_w = tmp_w;
+    l_w = t_w;
   }
 
   return (r_w * a_w) + l_w;
 }
 
+/* _tail_ob(): +feis:ob, also offsetting by 0x1.000 (as in +fynd:ob).
+**             correct over the domain [0x1.0000, 0xffff.ffff]
+*/
 static c3_w
-_tail(c3_w m_w)
+_tail_ob(c3_w m_w)
 {
-  c3_w c_w = _tail_fen(m_w);
-  return ( c_w < k_w ) ? c_w : _tail_fen(c_w);
+  c3_w c_w = _fen_ob(m_w - b_w);
+  return b_w + (( c_w < k_w ) ? c_w : _fen_ob(c_w));
 }
 
 u3_atom
@@ -62,10 +69,7 @@ u3qe_fynd_ob(u3_atom pyn)
   }
 
   if ( 2 == sor_w ) {
-    c3_w pyn_w = u3r_word(0, pyn);
-    c3_w out_w = b_w + _tail(pyn_w - b_w);
-
-    return u3i_word(out_w);
+    return u3i_word(_tail_ob(u3r_word(0, pyn)));
   }
   else {
     c3_w pyn_w[2];
@@ -75,7 +79,7 @@ u3qe_fynd_ob(u3_atom pyn)
       return u3k(pyn);
     }
     else {
-      pyn_w[0] = b_w + _tail(pyn_w[0] - b_w);
+      pyn_w[0] = _tail_ob(pyn_w[0]);
       return u3i_words(2, pyn_w);
     }
   }