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annotate libutil/tfo_msg_enc.c @ 275:def9f6e4f49e default tip

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doc/Use-outside-USA: Fake-NANP-numbers article is here
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 27 Nov 2023 21:49:19 -0800
parents 05d01e810217
children
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05d01e810217 libutil: add TFO message gen function based on Osmocom crc8gen
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1 /*
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2 * The function implemented in this module encodes a GSM 08.62 Extension_Block.
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3 */
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4
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5 #include <stdint.h>
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6 #include "osmo_bits.h"
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7
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8 /*
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9 * EFR TRAU parity
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10 *
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11 * g(x) = x^3 + x^1 + 1
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12 */
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13 static const struct osmo_crc8gen_code gsm0860_efr_crc3 = {
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14 .bits = 3,
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15 .poly = 0x3,
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16 .init = 0x0,
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17 .remainder = 0x7,
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18 };
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19
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20 void
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21 encode_tfo_ext_words(bits_2_10, bits_12_15, ex, out)
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22 unsigned bits_2_10, bits_12_15, ex;
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23 uint16_t *out;
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24 {
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25 ubit_t crc_in[13];
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26 uint8_t crc;
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27
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28 uint16_to_bits(bits_2_10, crc_in, 9);
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29 uint16_to_bits(bits_12_15, crc_in + 9, 4);
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30 crc = osmo_crc8gen_compute_bits(&gsm0860_efr_crc3, crc_in, 13);
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31 out[0] = bits_2_10;
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32 out[1] = (bits_12_15 << 5) | (crc << 2) | ex;
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33 }