Just for the record.
>> If the selected floating-point hardware includes the NEON extension (e.g.
>> -mfpu='neon'), note that floating-point operations are not generated by
>> GCC's auto-vectorization pass unless -funsafe-math-optimizations is also
>> specified. This is because NEON hardware does not fully implement the IEEE
>> 754 standard for floating-point arithmetic (in particular denormal values
>> are treated as zero), so the use of NEON instructions may lead to a loss of
>> precision.
Regarding loss of precision: my target is able to use '-mfpu=neon-vfpv4' which
selects floating point fused operations instead of chained. I tried it, but a
new test error surfaces due to accuracy (v3.7.0):
/src/gnuradio/build # ctest -V -R qa_ofdm_frame_equalizer_vcvc
UpdateCTestConfiguration from :/src/gnuradio/build/DartConfiguration.tcl
UpdateCTestConfiguration from :/src/gnuradio/build/DartConfiguration.tcl
Test project /src/gnuradio/build
Constructing a list of tests
Done constructing a list of tests
Checking test dependency graph...
Checking test dependency graph end
test 142
Start 142: qa_ofdm_frame_equalizer_vcvc
142: Test command: /bin/sh
"/src/gnuradio/build/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc_test.sh"
142: Test timeout computed to be: 9.99988e+06
142: .....F.
142: ======================================================================
142: FAIL: test_002_static (__main__.qa_ofdm_frame_equalizer_vcvc)
142: ----------------------------------------------------------------------
142: Traceback (most recent call last):
142: File
"/src/gnuradio/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc.py", line
244, in test_002_static
142: self.assertEqual(tag_dict, expected_dict)
142: AssertionError: {'frame_len': 4L, 'ofdm_sync_chan_taps': [0j, 0j,
(-2.2037331959268158e-08+1j), [truncated]... != {'frame_len': 4,
'ofdm_sync_chan_taps': [0, 0, 1j, 1j, 0, 1j, 1j, 0]}
142: + {'frame_len': 4, 'ofdm_sync_chan_taps': [0, 0, 1j, 1j, 0, 1j, 1j, 0]}
142: - {'frame_len': 4L,
142: - 'ofdm_sync_chan_taps': [0j,
142: - 0j,
142: - (-2.2037331959268158e-08+1j),
142: - (-2.2037331959268158e-08+1j),
142: - 0j,
142: - (2.2037331959268158e-08+1j),
142: - (-2.2037331959268158e-08+1j),
142: - 0j]}
So I went back to just '-mfpu=neon'.
I didn't log this as a GR bug, since it feels like the "Doctor, it hurts when I
do this" variety of problems.
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