Sotfmax bw inference fix

[calad0i]

Description

Fix edge in softmax stable impl norm_t type inference: consider fixed<2,2> *arr of range {-2,-1,0,1} max(arr) - arr can be all {0,1,2,3}, so iwidth and width shall be kept if was signed.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Tests

Checklist

• all

[JanFSchulte]

These test failures seem to be reproducible, so I think this requires a further check before merging:

FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vivado_io_parallel_resource] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vivado_io_parallel_latency] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vivado_io_stream_latency] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vivado_io_stream_resource] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vitis_io_parallel_resource] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vitis_io_parallel_latency] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vitis_io_stream_latency] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)
FAILED test_cnn_mnist_qkeras.py::test_accuracy[Vitis_io_stream_resource] - assert (0.988 > 0.92 and 0.011133603238866406 < 0.01)