core/conv: SCH decoding problem

Hi Tomas, I again have a question related to your SSE accelerated Viterbi decoder, and I hope it's the last issue, which prevents us from finishing this work. In short, SSE based implementation provides one-byte different decoding result for SCH transcoding test. So, the whole GSM 05.03 coding test fails. I have done some debugging, and would like to share some results. Have a look at the tests/coding/test_sch(), which first encodes a L3 packet into ubits and sbits, then some bits are getting destroyed, then the gsm0503_sch_decode() is being called to get decoded bytes back, and finally decoded bytes are being compared with original bytes. As long as encoder implementation is not covered by SSE code, it works as before. But SSE accelerated decoder outputs one-byte different result in case of SCH: int gsm0503_sch_decode(uint8_t *sb_info, sbit_t *burst) { ubit_t conv[35]; int rv; osmo_conv_decode(&gsm0503_sch, burst, conv); rv = osmo_crc16gen_check_bits(&gsm0503_sch_crc10, conv, 25, conv + 25); if (rv) return -1; // ... } // Original implementation ubit_t conv[35] = { 0x01 0x01 0x00 0x01 0x00 0x00 0x00 0x00 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x01 0x01 0x01 0x00 0x01 0x00 }; // Accelerated implementation ubit_t conv[35] = { 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x01 0x01 0x01 0x00 0x01 0x00 }; As you can see, the conv[3] isn't the same in both cases. So, at the next step the osmo_crc16gen_check_bits() returns -1. Latest version of this change: https://gerrit.osmocom.org/#/c/2454/ Do you have any ideas? Despite SCH decoding isn't required on BTS side, the problem may be more global, than the test shows. With best regards, Vadim Yanitskiy.