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[Relax][Frontend][TFLite] Read the keys vector byte width in FlexBufferDecoder #20830

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[Relax][Frontend][TFLite] Read the keys vector byte width in FlexBufferDecoder #20830

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9 changes: 7 additions & 2 deletions python/tvm/relax/frontend/tflite/tflite_flexbuffer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -135,10 +135,15 @@ def decode_map(self, end, byte_width, parent_byte_width):
size_fmt = {1: "<b", 2: "<h", 4: "<i", 8: "<q"}[byte_width]
map_size = struct.unpack(size_fmt, self.buffer[mid_loc - byte_width : mid_loc])[0]

# Find keys
# Find keys. The map header also stores the byte width of the keys vector, which is
# wider than one byte once a key string sits more than 255 bytes before it.
keys_offset = mid_loc - byte_width * 3
keys_end = self.indirect_jump(keys_offset, byte_width)
keys = self.decode_keys(keys_end, map_size, 1)
keys_byte_width_fmt = {1: "<B", 2: "<H", 4: "<I", 8: "<Q"}[byte_width]
keys_byte_width = struct.unpack(
keys_byte_width_fmt, self.buffer[mid_loc - byte_width * 2 : mid_loc - byte_width]
)[0]
keys = self.decode_keys(keys_end, map_size, keys_byte_width)

# Find values
values_end = self.indirect_jump(end, parent_byte_width)
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17 changes: 17 additions & 0 deletions tests/python/relax/test_frontend_tflite.py
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Expand Up @@ -3741,6 +3741,23 @@ def test_detection_postprocess_rejects_invalid_class_count():
_build_detection_postprocess_mod(num_classes=2, input_num_classes=5)


@pytest.mark.parametrize(
"custom_options",
[
pytest.param({f"option_{i}_" + "x" * 40: i for i in range(8)}, id="long_keys"),
pytest.param({f"key_{i:03d}": i for i in range(40)}, id="many_keys"),
],
)
def test_flexbuffer_decoder_wide_key_vector(custom_options):
# Over 255 bytes of key strings make the keys vector use 2-byte offsets.
from flatbuffers import flexbuffers

from tvm.relax.frontend.tflite.tflite_flexbuffer import FlexBufferDecoder

flexbuffer = bytes(flexbuffers.Dumps(custom_options))
assert FlexBufferDecoder(flexbuffer).decode() == custom_options


def _make_resize_expected(
input_shape, output_size, method, coordinate_transformation_mode, rounding_method
):
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