From eac235e3da6d2246b545cc6656a1f5b6f46f9abd Mon Sep 17 00:00:00 2001
From: Peter <peter.harpending@gmail.com>
Date: Thu, 11 May 2023 16:14:54 -0600
Subject: [PATCH] bitstring concat test cases

---
 libs/vdk/test/cases/testgen/bits.erl | 79 ++++++++++++++++++++++++----
 1 file changed, 69 insertions(+), 10 deletions(-)

diff --git a/libs/vdk/test/cases/testgen/bits.erl b/libs/vdk/test/cases/testgen/bits.erl
index b7b4053..2d14938 100644
--- a/libs/vdk/test/cases/testgen/bits.erl
+++ b/libs/vdk/test/cases/testgen/bits.erl
@@ -3,21 +3,80 @@
 -compile([export_all, nowarn_export_all]).
 
 
-empty() ->
-    <<>>.
-
-rand_bit() ->
-    case rand:uniform(2) of
-        1 -> <<0:1>>;
-        2 -> <<1:1>>
-    end.
-
 rand_bits(N) when N =< 8 ->
     <<Foo:N, _/bits>> = rand:bytes(1),
-    <<Foo:N>>.
+    <<Foo:N>>;
 rand_bits(N) when N > 8 ->
     Num_Bytes         = N div 8,
     Num_Trailing_Bits = N rem 8,
     <<( rand_bits(Num_Trailing_Bits) )/bits,
       ( rand:bytes(Num_Bytes)        )/binary>>.
 
+
+
+fmt(Bits) ->
+    io:format("~ts~n", [format_bits(Bits)]).
+
+
+
+format_bits(Bits) ->
+    ["<<", format_bits2(Bits), ">>"].
+
+
+format_bits2(Bits)                                          when 8 =< bit_size(Bits) ->
+    NBits  = bit_size(Bits),
+    NBytes = NBits div 8,
+    NRem   = NBits rem 8,
+    <<Bytes:NBytes/bytes, NewBits:NRem/bits>> = Bits,
+    case NRem of
+        0 ->
+            format_bytes(Bytes);
+        _ ->
+            [format_bytes(Bytes), ", ", format_bits2(NewBits)]
+    end;
+format_bits2(Bits = <<Start:4/bits, Rem/bits>>)             when 5 =< bit_size(Bits) ->
+    [format_bits2(Start), "_", format_bits2(Rem)];
+format_bits2(Bits = <<B:1, Rest/bits>>)                     when 1 =< bit_size(Bits) ->
+    case B of
+        0 ->
+            ["0", format_bits2(Rest)];
+        1 ->
+            ["1", format_bits2(Rest)]
+    end;
+format_bits2(<<>>) ->
+    [].
+
+
+%% hack: split into two groups of 4 bits
+format_bytes(<<A:4/bits, B:4/bits>>) ->
+    [format_bits2(A), "_", format_bits2(B)];
+%% byte_size(Rest) >= 1 by previous case
+format_bytes(<<N:1/bytes, Rest/bytes>>) ->
+    [format_bytes(N), ", ", format_bytes(Rest)];
+format_bytes(<<>>) ->
+    [].
+
+
+
+%% ten random cases for each pair of bit lengths, 0 =< N =< 8
+rand_cases() ->
+    rand_cases(0, 0, []).
+
+%% ten random cases for 
+rand_cases(8, 8, Acc) ->
+    [ten_cases(8, 8) | Acc];
+rand_cases(N, 8, Acc) ->
+    NewAcc = [ten_cases(N, 8) | Acc],
+    rand_cases(N + 1, 0, NewAcc);
+rand_cases(N, M, Acc) ->
+    rand_cases(N, M + 1, [ten_cases(N, M) | Acc]).
+
+
+ten_cases(N, M) ->
+    [cs(N, M) || _ <- lists:seq(1, 10)].
+
+cs(N, M) ->
+    A = rand_bits(N),
+    B = rand_bits(M),
+    C = <<A/bits, B/bits>>,
+    {A, B, C}.