From 6f39faeb7d75af7818e7fdc7f8e72769b3e9474e Mon Sep 17 00:00:00 2001
From: Joe Bryan <joemfb@gmail.com>
Date: Mon, 14 Sep 2020 15:20:42 -0700
Subject: [PATCH] u3: refactors u3a_walk_fore/unsafe(), using road stack api

---
 pkg/urbit/noun/allocate.c | 91 +++++++++++----------------------------
 1 file changed, 26 insertions(+), 65 deletions(-)

diff --git a/pkg/urbit/noun/allocate.c b/pkg/urbit/noun/allocate.c
index 6ab0317886..939b9e7987 100644
--- a/pkg/urbit/noun/allocate.c
+++ b/pkg/urbit/noun/allocate.c
@@ -2668,59 +2668,33 @@ u3a_walk_fore(u3_noun    a,
               void     (*pat_f)(u3_atom, void*),
               c3_o     (*cel_f)(u3_noun, void*))
 {
-  //  initialize signed stack offsets (relative to N or S road)
-  //
-  c3_o nor_o = u3a_is_north(u3R);
-  c3_ys mov_ys, off_ys;
-  {
-    c3_y wis_y = c3_wiseof(u3_noun);
-    mov_ys = ( c3y == nor_o ? -wis_y : wis_y );
-    off_ys = ( c3y == nor_o ? 0 : -wis_y );
-  }
+  u3_noun*   top;
+  u3a_pile pil_u;
 
-  //  set stack root, push argument
+  //  initialize stack control; push argument
   //
-  u3_noun *top, *don;
-  {
-    don         = u3to(u3_noun, u3R->cap_p + off_ys);
-    u3R->cap_p += mov_ys;
-    top         = u3to(u3_noun, u3R->cap_p + off_ys);
-    *top        = a;
-  }
+  u3a_pile_prep(&pil_u, sizeof(u3_noun));
+  top  = u3a_push(&pil_u);
+  *top = a;
 
-  while ( top != don ) {
+  while ( c3n == u3a_pile_done(&pil_u) ) {
     //  visit an atom, then pop the stack
     //
     if ( c3y == u3a_is_atom(a) ) {
       pat_f(a, ptr_v);
-      u3R->cap_p -= mov_ys;
-      top         = u3to(u3_noun, u3R->cap_p + off_ys);
+      top = u3a_pop(&pil_u);
     }
     //  vist a cell, if c3n, pop the stack
     //
     else if ( c3n == cel_f(a, ptr_v) ) {
-      u3R->cap_p -= mov_ys;
-      top         = u3to(u3_noun, u3R->cap_p + off_ys);
-
+      top = u3a_pop(&pil_u);
     }
     //  otherwise, push the tail and continue into the head
     //
     else {
-      *top        = u3t(a);
-      u3R->cap_p += mov_ys;
-
-      if ( c3y == nor_o ) {
-        if( !(u3R->cap_p > u3R->hat_p) ) {
-          u3m_bail(c3__meme);
-        }
-      }
-      else {
-        if( !(u3R->cap_p < u3R->hat_p) ) {
-          u3m_bail(c3__meme);
-        }
-      }
-
-      top  = u3to(u3_noun, u3R->cap_p + off_ys);
+      *top = u3t(a);
+      top  = u3a_push(&pil_u);
+      u3a_pile_sane(&pil_u);
       *top = u3h(a);
     }
 
@@ -2736,48 +2710,35 @@ u3a_walk_fore_unsafe(u3_noun    a,
                      void     (*pat_f)(u3_atom, void*),
                      c3_o     (*cel_f)(u3_noun, void*))
 {
-  //  initialize signed stack offsets (relative to N or S road)
-  //
-  c3_ys mov_ys, off_ys;
-  {
-    c3_y wis_y = c3_wiseof(u3_noun);
-    c3_o nor_o = u3a_is_north(u3R);
-    mov_ys = ( c3y == nor_o ? -wis_y : wis_y );
-    off_ys = ( c3y == nor_o ? 0 : -wis_y );
-  }
+  u3_noun*   top;
+  u3a_pile pil_u;
 
-  //  set stack root, push argument
+  //  initialize stack control; push argument
   //
-  u3_noun *top, *don;
-  {
-    don         = u3to(u3_noun, u3R->cap_p + off_ys);
-    u3R->cap_p += mov_ys;
-    top         = u3to(u3_noun, u3R->cap_p + off_ys);
-    *top        = a;
-  }
+  u3a_pile_prep(&pil_u, sizeof(u3_noun));
+  top  = u3a_push(&pil_u);
+  *top = a;
 
-  while ( top != don ) {
+  while ( c3n == u3a_pile_done(&pil_u) ) {
     //  visit an atom, then pop the stack
     //
     if ( c3y == u3a_is_atom(a) ) {
       pat_f(a, ptr_v);
-      u3R->cap_p -= mov_ys;
-      top         = u3to(u3_noun, u3R->cap_p + off_ys);
+      top = u3a_pop(&pil_u);
     }
     //  vist a cell, if c3n, pop the stack
     //
     else if ( c3n == cel_f(a, ptr_v) ) {
-      u3R->cap_p -= mov_ys;
-      top         = u3to(u3_noun, u3R->cap_p + off_ys);
-
+      top = u3a_pop(&pil_u);
     }
     //  otherwise, push the tail and continue into the head
     //
     else {
-      *top        = u3t(a);
-      u3R->cap_p += mov_ys;
-      top         = u3to(u3_noun, u3R->cap_p + off_ys);
-      *top        = u3h(a);
+      *top = u3t(a);
+      //  NB: overflow check elided here
+      //
+      top  = u3a_push(&pil_u);
+      *top = u3h(a);
     }
 
     a = *top;