From ecb9c23e0811e219ac622133add5c1524c35e649 Mon Sep 17 00:00:00 2001
From: Joe Bryan <joemfb@gmail.com>
Date: Mon, 28 Sep 2020 11:30:42 -0700
Subject: [PATCH] u3: adds u3i_slab_from(), removes unnecessary uses of
 u3r_chop()

---
 pkg/urbit/include/noun/imprison.h |  5 +++++
 pkg/urbit/jets/c/cat.c            |  3 +--
 pkg/urbit/jets/c/con.c            |  5 +----
 pkg/urbit/jets/c/dis.c            |  5 +----
 pkg/urbit/jets/c/mix.c            |  7 +++----
 pkg/urbit/noun/imprison.c         | 12 ++++++++++++
 6 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/pkg/urbit/include/noun/imprison.h b/pkg/urbit/include/noun/imprison.h
index 7c5e55c0b..577cec02f 100644
--- a/pkg/urbit/include/noun/imprison.h
+++ b/pkg/urbit/include/noun/imprison.h
@@ -32,6 +32,11 @@
           void
           u3i_slab_bare(u3i_slab* sab_u, c3_g met_g, c3_w len_w);
 
+        /* u3i_slab_from(): configure bloq-length slab, initialize with [a].
+        */
+          void
+          u3i_slab_from(u3i_slab* sab_u, u3_atom a, c3_g met_g, c3_w len_w);
+
         /* u3i_slab_grow(): resize slab, reallocating as necessary.
         */
           void
diff --git a/pkg/urbit/jets/c/cat.c b/pkg/urbit/jets/c/cat.c
index 0851ddc7c..2648c2303 100644
--- a/pkg/urbit/jets/c/cat.c
+++ b/pkg/urbit/jets/c/cat.c
@@ -25,9 +25,8 @@
       }
       else {
         u3i_slab sab_u;
-        u3i_slab_init(&sab_u, a_g, all_w);
+        u3i_slab_from(&sab_u, b, a_g, all_w);
 
-        u3r_chop(a_g, 0, lew_w, 0, sab_u.buf_w, b);
         u3r_chop(a_g, 0, ler_w, lew_w, sab_u.buf_w, c);
 
         return u3i_slab_mint(&sab_u);
diff --git a/pkg/urbit/jets/c/con.c b/pkg/urbit/jets/c/con.c
index 09db8cbc4..9fa8df142 100644
--- a/pkg/urbit/jets/c/con.c
+++ b/pkg/urbit/jets/c/con.c
@@ -20,10 +20,7 @@
       c3_w     len_w = c3_max(lna_w, lnb_w);
       c3_w       i_w;
       u3i_slab sab_u;
-
-      u3i_slab_init(&sab_u, 5, len_w);
-
-      u3r_chop(5, 0, lna_w, 0, sab_u.buf_w, a);
+      u3i_slab_from(&sab_u, a, 5, len_w);
 
       for ( i_w = 0; i_w < lnb_w; i_w++ ) {
         sab_u.buf_w[i_w] |= u3r_word(i_w, b);
diff --git a/pkg/urbit/jets/c/dis.c b/pkg/urbit/jets/c/dis.c
index cdeae3dd2..a0f478a94 100644
--- a/pkg/urbit/jets/c/dis.c
+++ b/pkg/urbit/jets/c/dis.c
@@ -20,10 +20,7 @@
       c3_w     len_w = c3_max(lna_w, lnb_w);
       c3_w       i_w;
       u3i_slab sab_u;
-
-      u3i_slab_init(&sab_u, 5, len_w);
-
-      u3r_chop(5, 0, lna_w, 0, sab_u.buf_w, a);
+      u3i_slab_from(&sab_u, a, 5, len_w);
 
       for ( i_w = 0; i_w < len_w; i_w++ ) {
         sab_u.buf_w[i_w] &= (i_w >= lnb_w) ? 0 : u3r_word(i_w, b);
diff --git a/pkg/urbit/jets/c/mix.c b/pkg/urbit/jets/c/mix.c
index bc013dabc..ccb008c05 100644
--- a/pkg/urbit/jets/c/mix.c
+++ b/pkg/urbit/jets/c/mix.c
@@ -20,11 +20,10 @@
       c3_w     len_w = c3_max(lna_w, lnb_w);
       c3_w       i_w;
       u3i_slab sab_u;
+      u3i_slab_from(&sab_u, a, 5, len_w);
 
-      u3i_slab_init(&sab_u, 5, len_w);
-
-      u3r_chop(5, 0, lna_w, 0, sab_u.buf_w, a);
-
+      //  XX use u3r_chop for XOR?
+      //
       for ( i_w = 0; i_w < lnb_w; i_w++ ) {
         sab_u.buf_w[i_w] ^= u3r_word(i_w, b);
       }
diff --git a/pkg/urbit/noun/imprison.c b/pkg/urbit/noun/imprison.c
index 2ae4dd70e..13198d209 100644
--- a/pkg/urbit/noun/imprison.c
+++ b/pkg/urbit/noun/imprison.c
@@ -155,6 +155,18 @@ u3i_slab_bare(u3i_slab* sab_u, c3_g met_g, c3_w len_w)
   u3t_off(mal_o);
 }
 
+/* u3i_slab_from(): configure bloq-length slab, initialize with [a].
+*/
+void
+u3i_slab_from(u3i_slab* sab_u, u3_atom a, c3_g met_g, c3_w len_w)
+{
+  u3i_slab_bare(sab_u, met_g, len_w);
+
+  //  copies [a], zero-initializes any additional space
+  //
+  u3r_words(0, sab_u->wor_w, sab_u->buf_w, a);
+}
+
 /* u3i_slab_grow(): resize slab, reallocating as necessary.
 */
 void