FreeCalypso > hg > gsm-codec-lib
view libgsmfr2/prng.c @ 261:cfcb3ce9c778
libgsmfr2: implement gsmfr_unpack_to_array()
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Fri, 12 Apr 2024 23:29:18 +0000 |
parents | a33edf624061 |
children | 573afa985df6 |
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/* * We use a pseudorandom sequence generator function in two places: * when generating comfort noise (GSM 06.12 section 6.1), and when * randomizing grid position parameters as part of speech muting * during error handling (GSM 06.11 section 6). * * Our PRNG is a copy of the pseudonoise() function from ETSI EFR code, * where it is used for similar purposes. */ #include <stdint.h> #include "tw_gsmfr.h" #include "pp_internal.h" uint16_t gsmfr_preproc_prng(struct gsmfr_preproc_state *st, uint16_t no_bits) { uint16_t noise_bits, Sn, i; noise_bits = 0; for (i = 0; i < no_bits; i++) { /* State n == 31 */ if ((st->cn_random_lfsr & 0x00000001L) != 0) { Sn = 1; } else { Sn = 0; } /* State n == 3 */ if ((st->cn_random_lfsr & 0x10000000L) != 0) { Sn = Sn ^ 1; } else { Sn = Sn ^ 0; } noise_bits = noise_bits << 1; noise_bits = noise_bits | st->cn_random_lfsr & 1; st->cn_random_lfsr >>= 1; if (Sn & 1) { st->cn_random_lfsr |= 0x40000000L; } } return noise_bits; }