Make sub-binaries of sub-binaries sub-binaries

Fix a bug where sub-binaries of sub-binaries were reallocated, thus wasting memory. Signed-off-by: Paul Guyot <[email protected]>
atomvm · Oct 28, 2023 · dcc47d3 · dcc47d3
1 parent 92eed62
commit dcc47d3
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Showing 2 changed files with 23 additions and 3 deletions.
diff --git a/src/libAtomVM/term.h b/src/libAtomVM/term.h
@@ -1040,6 +1040,9 @@ static inline term term_maybe_create_sub_binary(term binary, size_t offset, size
 {
     if (term_is_refc_binary(binary) && len >= SUB_BINARY_MIN) {
         return term_alloc_sub_binary(binary, offset, len, heap);
+    } else if (term_is_sub_binary(binary) && len >= SUB_BINARY_MIN) {
+        const term *boxed_value = term_to_const_term_ptr(binary);
+        return term_alloc_sub_binary(boxed_value[3], boxed_value[2] + offset, len, heap);
     } else {
         const char *data = term_binary_data(binary);
         return term_from_literal_binary(data + offset, len, heap, glb);

diff --git a/tests/erlang_tests/test_sub_binaries.erl b/tests/erlang_tests/test_sub_binaries.erl
@@ -56,6 +56,7 @@ start() ->
 
 test_common() ->
     ok = run_test(fun() -> test_count_binary() end),
+    ok = run_test(fun() -> test_sub_sub_binary() end),
     ok.
 
 test_atom() ->
@@ -72,6 +73,14 @@ test_atom() ->
     ok = run_test(fun() -> test_bit_syntax_get_binary() end),
     ok.
 
+test_sub_sub_binary() ->
+    Bin = create_binary(get_largest_heap_binary_size()),
+
+    SubBin = binary:part(Bin, 1, 7),
+    <<2, 3, 4, 5, 6, 7, 8>> = SubBin,
+    <<4, 5, 6, 7, 8>> = binary:part(SubBin, 2, 5),
+    ok.
+
 test_heap_sub_binary() ->
     MemoryBinarySize = erlang:memory(binary),
     HeapSize0 = get_heap_size(),
@@ -80,7 +89,7 @@ test_heap_sub_binary() ->
     HeapSize1 = get_heap_size(),
     ?VERIFY(HeapSize0 < HeapSize1),
 
-    SubBin = binary:part(Bin, 1, 7),
+    SubBin = binary:part(Bin, 1, 47),
     HeapSize2 = get_heap_size(),
     ?VERIFY(HeapSize1 < HeapSize2),
     ?VERIFY((HeapSize2 - HeapSize1) >= 8),
@@ -104,11 +113,19 @@ test_const_sub_binary() ->
 
     LargeSubBin = binary:part(?LITERAL_BIN, 1, BinarySize - 1),
     HeapSize2 = get_heap_size(),
-    ?VERIFY(HeapSize2 < HeapSize1 + erlang:byte_size(LargeSubBin)),
+    ?VERIFY((HeapSize2 - HeapSize1) >= 8),
+    ?VERIFY((HeapSize2 - HeapSize1) < BinarySize div 4),
+    ?VERIFY(MemoryBinarySize == erlang:memory(binary)),
+
+    SubSubBin = binary:part(LargeSubBin, 0, BinarySize - 2),
+    HeapSize3 = get_heap_size(),
+    ?VERIFY((HeapSize3 - HeapSize2) >= 8),
+    ?VERIFY((HeapSize3 - HeapSize2) < BinarySize div 4),
     ?VERIFY(MemoryBinarySize == erlang:memory(binary)),
 
     id(SmallSubBin),
     id(LargeSubBin),
+    id(SubSubBin),
     ok.
 
 test_non_const_sub_binary() ->
@@ -126,7 +143,7 @@ test_non_const_sub_binary() ->
 
     LargeSubBin = binary:part(Bin, 1, BinarySize - 1),
     HeapSize3 = get_heap_size(),
-    ?VERIFY(HeapSize3 < HeapSize2 + erlang:byte_size(LargeSubBin)),
+    ?VERIFY((HeapSize3 - HeapSize2) < BinarySize div 4),
     ?VERIFY(MemoryBinarySize + 1024 == erlang:memory(binary)),
 
     id(String),