beam_asm: Speed up encoding of large numbers

The misc_SUITE:integer_encoding/1 test case is annoyingly slow.

Rewrite the encoding of integers in beam_asm to use the
binary:encode_unsigned/1 BIF.

Also tweak the test case itself. Scale the down the maximum
size of the numbers being generated, but also add test of
numbers around boundaries of power of two (which are the numbers
most likely to expose bugs in the encoding).

1 files changed, 17 insertions, 27 deletions

diff --git a/lib/compiler/src/beam_asm.erl b/lib/compiler/src/beam_asm.erl
index 084686def7..73694b96ce 100644
--- a/lib/compiler/src/beam_asm.erl
+++ b/lib/compiler/src/beam_asm.erl
@@ -431,45 +431,35 @@ encode_alloc_list_1([], Dict, Acc) ->
     {iolist_to_binary(Acc),Dict}.
 
 encode(Tag, N) when N < 0 ->
-    encode1(Tag, negative_to_bytes(N, []));
+    encode1(Tag, negative_to_bytes(N));
 encode(Tag, N) when N < 16 ->
     (N bsl 4) bor Tag;
 encode(Tag, N) when N < 16#800  ->
     [((N bsr 3) band 2#11100000) bor Tag bor 2#00001000, N band 16#ff];
 encode(Tag, N) ->
-    encode1(Tag, to_bytes(N, [])).
+    encode1(Tag, to_bytes(N)).
 
 encode1(Tag, Bytes) ->
-    case length(Bytes) of
+    case iolist_size(Bytes) of
 	Num when 2 =< Num, Num =< 8 ->
 	    [((Num-2) bsl 5) bor 2#00011000 bor Tag| Bytes];
 	Num when 8 < Num ->
 	    [2#11111000 bor Tag, encode(?tag_u, Num-9)| Bytes]
     end.
 
-
-to_bytes(N0, Acc) ->
-    Bits = 3*128,
-    case N0 bsr Bits of
-	0 ->
-	    to_bytes_1(N0, Acc);
-	N ->
-	    to_bytes(N, binary_to_list(<<N0:Bits>>) ++ Acc)
-    end.
-    
-to_bytes_1(0, [B|_]=Done) when B < 128 -> Done;
-to_bytes_1(N, Acc) -> to_bytes(N bsr 8, [N band 16#ff|Acc]).
-
-negative_to_bytes(N0, Acc) ->
-    Bits = 3*128,
-    case N0 bsr Bits of
-	-1 ->
-	    negative_to_bytes_1(N0, Acc);
-	N ->
-	    negative_to_bytes_1(N, binary_to_list(<<N0:Bits>>) ++ Acc)
+to_bytes(N) ->
+    Bin = binary:encode_unsigned(N),
+    case Bin of
+	<<0:1,_/bits>> -> Bin;
+	<<1:1,_/bits>> -> [0,Bin]
     end.
 
-negative_to_bytes_1(-1, [B1,_B2|_]=Done) when B1 > 127 ->
-    Done;
-negative_to_bytes_1(N, Acc) ->
-    negative_to_bytes_1(N bsr 8, [N band 16#ff|Acc]).
+negative_to_bytes(N) when N >= -16#8000 ->
+    <<N:16>>;
+negative_to_bytes(N) ->
+    Bytes = byte_size(binary:encode_unsigned(-N)),
+    Bin = <<N:Bytes/unit:8>>,
+    case Bin of
+	<<0:1,_/bits>> -> [16#ff,Bin];
+	<<1:1,_/bits>> -> Bin
+    end.