repn jets pass without jet.

pkg/arvo/tests/sys/hoon/bits.hoon

@@ -1,9 +1,15 @@
 /+  *test
 |%
+++  repn
+  |=  [bits=@ud x=(list @)]
+  =|  c=@ud
+  |-  ^-  @
+  ?~  x  0
+  (add (lsh 0 (mul bits c) (end 0 bits i.x)) $(c +(c), x t.x))
 ++  test-bits
   ;:  weld
     ::
-    ::  Random sanity testing
+    ::  ripn: Random sanity testing
     ::
     %+  expect-eq
       !>  ~[0x3 0x7 0x7]
@@ -15,13 +21,13 @@
       !>  ~[0x1 0xe 0xe 0xf 0xf]
       !>  (flop (ripn 4 0x1.eeff))
     ::
-    :: Typical use-cases
+    :: ripn: Typical use-cases
     ::
     %+  expect-eq
       !>  ~[0x1 0x23.4567 0x89.abcd]
       !>  (flop (ripn 24 0x1.2345.6789.abcd))
     ::
-    ::  Edge cases
+    ::  ripn: Edge cases
     ::
     %+  expect-eq
       !>  ~
@@ -30,7 +36,7 @@
       !>  ~
       !>  (flop (ripn 1 0x0))
     ::
-    ::  Word boundaries
+    ::  ripn: Word boundaries
     ::
     %+  expect-eq
       !>  ~[0x7fff.ffff]
@@ -50,6 +56,54 @@
     %+  expect-eq
       !>  ~[0x123 0x456 0x789 0xabc 0xdef 0x12 0x345 0x678]
       !>  (flop (ripn 12 0x1234.5678.9abc.def0.1234.5678))
+    ::
+    ::  repn: Random sanity testing
+    ::
+    %+  expect-eq
+      !>  0xff
+      !>  (repn 3 (flop ~[0x3 0x7 0x7]))
+    %+  expect-eq
+      !>  0x1.eeff
+      !>  (repn 8 (flop ~[0x1 0xee 0xff]))
+    %+  expect-eq
+      !>  0x1.eeff
+      !>  (repn 4 (flop ~[0x1 0xe 0xe 0xf 0xf]))
+    ::
+    :: repn: Typical use-cases
+    ::
+    %+  expect-eq
+      !>  0x1.2345.6789.abcd
+      !>  (repn 24 (flop ~[0x1 0x23.4567 0x89.abcd]))
+    ::
+    ::  repn: Edge cases
+    ::
+    %+  expect-eq
+      !>  0x0
+      !>  (repn 31 (flop ~))
+    %+  expect-eq
+      !>  0x0
+      !>  (repn 1 (flop ~))
+    ::
+    ::  repn: Word boundaries
+    ::
+    %+  expect-eq
+      !>  0x7fff.ffff
+      !>  (repn 31 (flop ~[0x7fff.ffff]))
+    %+  expect-eq
+      !>  0xffff.ffff
+      !>  (repn 31 (flop ~[0x1 0x7fff.ffff]))
+    %+  expect-eq
+      !>  0x1.ffff.ffff
+      !>  (repn 31 (flop ~[0x3 0x7fff.ffff]))
+    %+  expect-eq
+      !>  0xffff.ffff.ffff.ffff
+      !>  (repn 31 (flop ~[0x3 0x7fff.ffff 0x7fff.ffff]))
+    %+  expect-eq
+      !>  0x7.ffff.ffff
+      !>  (repn 17 (flop ~[0x1 0x1.ffff 0x1.ffff]))
+    %+  expect-eq
+      !>  0x1234.5678.9abc.def0.1234.5678
+      !>  (repn 12 (flop ~[0x123 0x456 0x789 0xabc 0xdef 0x12 0x345 0x678]))
   ==
 ::
 --

pkg/urbit/jets/c/repn.c

@@ -0,0 +1,74 @@
+#include "all.h"
+
+/*
+  Get the lowest `n` bits of a word `w` using a bitmask.
+*/
+#define TAKEBITS(n,w) \
+  ((n)==32) ? (w) :   \
+  ((n)==0)  ? 0   :   \
+  ((w) & ((1 << (n)) - 1))
+
+/*
+  Divide, rounding up.
+*/
+#define DIVCEIL(x,y) \
+  (x==0) ? 0 :       \
+  1 + ((x - 1) / y);
+
+u3_noun u3qc_repn(u3_atom bits, u3_atom atom) {
+  if ( !_(u3a_is_cat(bits) || bits==0 || bits>31) ) {
+    return u3m_bail(c3__fail);
+  }
+
+  c3_w bit_width  = u3r_met(0, atom);
+  c3_w num_blocks = DIVCEIL(bit_width, bits);
+
+  u3_noun res = u3_nul;
+
+  for ( c3_w blk = 0; blk < num_blocks; blk++ ) {
+    c3_w next_blk = blk + 1;
+    c3_w blks_rem = num_blocks - next_blk;
+    c3_w bits_rem = blks_rem * bits;
+    c3_w ins_idx  = bits_rem / 32;
+    c3_w sig_idx  = ins_idx + 1;
+
+    c3_w bits_rem_in_ins_word = bits_rem % 32;
+
+    c3_w ins_word  = u3r_word(ins_idx, atom);
+    c3_w sig_word  = u3r_word(sig_idx, atom);
+    c3_w nbits_ins = c3_min(bits, 32 - bits_rem_in_ins_word);
+    c3_w nbits_sig = bits - nbits_ins;
+
+    c3_w ins_word_bits = TAKEBITS(nbits_ins, ins_word >> bits_rem_in_ins_word);
+    c3_w sig_word_bits = TAKEBITS(nbits_sig, sig_word);
+
+    c3_w item = ins_word_bits | (sig_word_bits << nbits_ins);
+
+    res = u3nc(item, res);
+  }
+
+  return res;
+}
+
+u3_noun u3wc_repn(u3_noun cor) {
+  u3_noun bits, atom=0;
+
+  u3l_log("WE'RE ALL GOING TO DIE\n");
+
+  return 0;
+
+  if ( (c3n == u3r_mean(cor, u3x_sam_2, &bits, u3x_sam_3, &atom, 0)) ||
+       (c3n == u3ud(bits)) ||
+       (c3n == u3ud(atom)) )
+  {
+    return u3m_bail(c3__exit);
+  }
+
+  return u3qc_repn(bits, atom);
+}
+
+u3_noun u3kc_repn(u3_atom bits, u3_atom atom) {
+  u3_noun res = u3qc_repn(bits, atom);
+  u3z(bits), u3z(atom);
+  return res;
+}