diff options
| -rw-r--r-- | include/osmocom/core/conv.h | 31 | ||||
| -rw-r--r-- | src/conv.c | 126 |
2 files changed, 119 insertions, 38 deletions
diff --git a/include/osmocom/core/conv.h b/include/osmocom/core/conv.h index ba490b45..159a055b 100644 --- a/include/osmocom/core/conv.h +++ b/include/osmocom/core/conv.h @@ -35,6 +35,19 @@ #include <osmocom/core/bits.h> +/*! \brief possibe termination types + * + * The termination type will determine which state the encoder/decoder + * can start/end with. This is mostly taken care of in the high level API + * call. So if you use the low level API, you must take care of making the + * proper calls yourself. + */ +enum osmo_conv_term { + CONV_TERM_FLUSH = 0, /*!< \brief Flush encoder state */ + CONV_TERM_TRUNCATION, /*!< \brief Direct truncation */ + CONV_TERM_TAIL_BITING, /*!< \brief Tail biting */ +}; + /*! \brief structure describing a given convolutional code * * The only required fields are N,K and the next_output/next_state arrays. The @@ -46,6 +59,8 @@ struct osmo_conv_code { int K; /*!< \brief Constraint length */ int len; /*!< \brief # of data bits */ + enum osmo_conv_term term; /*!< \brief Termination type */ + const uint8_t (*next_output)[2];/*!< \brief Next output array */ const uint8_t (*next_state)[2]; /*!< \brief Next state array */ @@ -70,9 +85,11 @@ struct osmo_conv_encoder { void osmo_conv_encode_init(struct osmo_conv_encoder *encoder, const struct osmo_conv_code *code); +void osmo_conv_encode_load_state(struct osmo_conv_encoder *encoder, + const ubit_t *input); int osmo_conv_encode_raw(struct osmo_conv_encoder *encoder, const ubit_t *input, ubit_t *output, int n); -int osmo_conv_encode_finish(struct osmo_conv_encoder *encoder, ubit_t *output); +int osmo_conv_encode_flush(struct osmo_conv_encoder *encoder, ubit_t *output); /* All-in-one */ int osmo_conv_encode(const struct osmo_conv_code *code, @@ -100,16 +117,18 @@ struct osmo_conv_decoder { }; void osmo_conv_decode_init(struct osmo_conv_decoder *decoder, - const struct osmo_conv_code *code, int len); -void osmo_conv_decode_reset(struct osmo_conv_decoder *decoder); + const struct osmo_conv_code *code, + int len, int start_state); +void osmo_conv_decode_reset(struct osmo_conv_decoder *decoder, int start_state); +void osmo_conv_decode_rewind(struct osmo_conv_decoder *decoder); void osmo_conv_decode_deinit(struct osmo_conv_decoder *decoder); int osmo_conv_decode_scan(struct osmo_conv_decoder *decoder, const sbit_t *input, int n); -int osmo_conv_decode_finish(struct osmo_conv_decoder *decoder, - const sbit_t *input); +int osmo_conv_decode_flush(struct osmo_conv_decoder *decoder, + const sbit_t *input); int osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, - ubit_t *output, int has_finish); + ubit_t *output, int has_flush, int end_state); /* All-in-one */ int osmo_conv_decode(const struct osmo_conv_code *code, @@ -57,6 +57,19 @@ osmo_conv_encode_init(struct osmo_conv_encoder *encoder, encoder->code = code; } +void +osmo_conv_encode_load_state(struct osmo_conv_encoder *encoder, + const ubit_t *input) +{ + int i; + uint8_t state = 0; + + for (i=0; i<(encoder->code->K-1); i++) + state = (state << 1) | input[i]; + + encoder->state = state; +} + static inline int _conv_encode_do_output(struct osmo_conv_encoder *encoder, uint8_t out, ubit_t *output) @@ -117,8 +130,8 @@ osmo_conv_encode_raw(struct osmo_conv_encoder *encoder, } int -osmo_conv_encode_finish(struct osmo_conv_encoder *encoder, - ubit_t *output) +osmo_conv_encode_flush(struct osmo_conv_encoder *encoder, + ubit_t *output) { const struct osmo_conv_code *code = encoder->code; uint8_t state; @@ -159,8 +172,8 @@ osmo_conv_encode_finish(struct osmo_conv_encoder *encoder, * \return Number of produced output bits * * This is an all-in-one function, taking care of - * \ref osmo_conv_init, \ref osmo_conv_encode_raw and - * \ref osmo_conv_encode_finish. + * \ref osmo_conv_init, \ref osmo_conv_encode_load_state, + * \ref osmo_conv_encode_raw and \ref osmo_conv_encode_flush as needed. */ int osmo_conv_encode(const struct osmo_conv_code *code, @@ -170,8 +183,16 @@ osmo_conv_encode(const struct osmo_conv_code *code, int l; osmo_conv_encode_init(&encoder, code); - l = osmo_conv_encode_raw(&encoder, input, output, code->len); - l += osmo_conv_encode_finish(&encoder, &output[l]); + + if (code->term == CONV_TERM_TAIL_BITING) { + int eidx = code->len - code->K + 1; + osmo_conv_encode_load_state(&encoder, &input[eidx]); + } + + l = osmo_conv_encode_raw(&encoder, input, output, code->len); + + if (code->term == CONV_TERM_FLUSH) + l += osmo_conv_encode_flush(&encoder, &output[l]); return l; } @@ -185,7 +206,7 @@ osmo_conv_encode(const struct osmo_conv_code *code, void osmo_conv_decode_init(struct osmo_conv_decoder *decoder, - const struct osmo_conv_code *code, int len) + const struct osmo_conv_code *code, int len, int start_state) { int n_states; @@ -208,11 +229,11 @@ osmo_conv_decode_init(struct osmo_conv_decoder *decoder, decoder->state_history = malloc(sizeof(uint8_t) * n_states * (len + decoder->code->K - 1)); /* Classic reset */ - osmo_conv_decode_reset(decoder); + osmo_conv_decode_reset(decoder, start_state); } void -osmo_conv_decode_reset(struct osmo_conv_decoder *decoder) +osmo_conv_decode_reset(struct osmo_conv_decoder *decoder, int start_state) { int i; @@ -220,14 +241,39 @@ osmo_conv_decode_reset(struct osmo_conv_decoder *decoder) decoder->o_idx = 0; decoder->p_idx = 0; - /* Initial error (only state 0 is valid) */ - decoder->ae[0] = 0; - for (i=1; i<decoder->n_states; i++) { - decoder->ae[i] = MAX_AE; + /* Initial error */ + if (start_state < 0) { + /* All states possible */ + memset(decoder->ae, 0x00, sizeof(unsigned int) * decoder->n_states); + } else { + /* Fixed start state */ + for (i=0; i<decoder->n_states; i++) { + decoder->ae[i] = (i == start_state) ? 0 : MAX_AE; + } } } void +osmo_conv_decode_rewind(struct osmo_conv_decoder *decoder) +{ + int i; + unsigned int min_ae = MAX_AE; + + /* Reset indexes */ + decoder->o_idx = 0; + decoder->p_idx = 0; + + /* Initial error normalize (remove constant) */ + for (i=0; i<decoder->n_states; i++) { + if (decoder->ae[i] < min_ae) + min_ae = decoder->ae[i]; + } + + for (i=0; i<decoder->n_states; i++) + decoder->ae[i] -= min_ae; +} + +void osmo_conv_decode_deinit(struct osmo_conv_decoder *decoder) { free(decoder->ae); @@ -339,8 +385,8 @@ osmo_conv_decode_scan(struct osmo_conv_decoder *decoder, } int -osmo_conv_decode_finish(struct osmo_conv_decoder *decoder, - const sbit_t *input) +osmo_conv_decode_flush(struct osmo_conv_decoder *decoder, + const sbit_t *input) { const struct osmo_conv_code *code = decoder->code; @@ -445,7 +491,7 @@ osmo_conv_decode_finish(struct osmo_conv_decoder *decoder, int osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, - ubit_t *output, int has_finish) + ubit_t *output, int has_flush, int end_state) { const struct osmo_conv_code *code = decoder->code; @@ -455,20 +501,26 @@ osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, uint8_t *sh_ptr; - /* Find state with least error */ - min_ae = MAX_AE; - min_state = 0xff; + /* End state ? */ + if (end_state < 0) { + /* Find state with least error */ + min_ae = MAX_AE; + min_state = 0xff; - for (s=0; s<decoder->n_states; s++) - { - if (decoder->ae[s] < min_ae) { - min_ae = decoder->ae[s]; - min_state = s; + for (s=0; s<decoder->n_states; s++) + { + if (decoder->ae[s] < min_ae) { + min_ae = decoder->ae[s]; + min_state = s; + } } - } - if (min_state == 0xff) - return -1; + if (min_state == 0xff) + return -1; + } else { + min_state = (uint8_t) end_state; + min_ae = decoder->ae[end_state]; + } /* Traceback */ cur_state = min_state; @@ -478,7 +530,7 @@ osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, sh_ptr = &decoder->state_history[decoder->n_states * (n-1)]; /* No output for the K-1 termination input bits */ - if (has_finish) { + if (has_flush) { for (i=0; i<code->K-1; i++) { cur_state = sh_ptr[cur_state]; sh_ptr -= decoder->n_states; @@ -510,7 +562,7 @@ osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, * * This is an all-in-one function, taking care of * \ref osmo_conv_decode_init, \ref osmo_conv_decode_scan, - * \ref osmo_conv_decode_finish, \ref osmo_conv_decode_get_output and + * \ref osmo_conv_decode_flush, \ref osmo_conv_decode_get_output and * \ref osmo_conv_decode_deinit. */ int @@ -520,12 +572,22 @@ osmo_conv_decode(const struct osmo_conv_code *code, struct osmo_conv_decoder decoder; int rv, l; - osmo_conv_decode_init(&decoder, code, 0); + osmo_conv_decode_init(&decoder, code, 0, 0); + + if (code->term == CONV_TERM_TAIL_BITING) { + osmo_conv_decode_scan(&decoder, input, code->len); + osmo_conv_decode_rewind(&decoder); + } l = osmo_conv_decode_scan(&decoder, input, code->len); - l = osmo_conv_decode_finish(&decoder, &input[l]); - rv = osmo_conv_decode_get_output(&decoder, output, 1); + if (code->term == CONV_TERM_FLUSH) + l = osmo_conv_decode_flush(&decoder, &input[l]); + + rv = osmo_conv_decode_get_output(&decoder, output, + code->term == CONV_TERM_FLUSH, /* has_flush */ + code->term == CONV_TERM_FLUSH ? 0 : -1 /* end_state */ + ); osmo_conv_decode_deinit(&decoder); |