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Sylvain Munaut 246tnt at gmail.comHi Thomas,
I've just only seen this. I'll try to test and comment on them ASAP.
Some quick things I saw from a quick glance though:
- Some things that should be 'static' are not and they pollute the
global namespace
- Anything that is in the global namespace needs the osmo_ (or even
osmo_conv_ here) prefix
- Did you check (and test in make test) that it works for all codes
that matches
"if ((code->N <= 4) && ((code->K == 5) || (code->K == 7)))" ?
- The viterbi_gen file seems fairly easy to generate, maybe in the
future it'd be worth autogenerating it
Also, to avoid exporting those internal symbols, I'm wondering if
#including the viterbi_gen.c from viterbi.c instead of compiling
separately wouldn't be better. But that's just a random idea ...
> A beneficial change would be to modify the API to allow persistent
> decoder objects instead of performing an allocation and tear-down on
> every decoding call. From a performance standpoint, the current
> implementation is unnecessarily restricted by memory access and page
> faults for that reason.
You can't change the existing API without breaking existing stuff, but you can
add a new all-in-one function that allows to give a persistent decoder object.
like osmo_conv_decode_persist or whatever you want to call it.
Cheers,
Sylvain
On Tue, Apr 29, 2014 at 6:12 AM, Thomas Tsou <tom at tsou.cc> wrote:
> Add a separate, faster convolution decoding implementation for rates
> up to N=4 and constraint lengths of K=5 and K=7, which covers the
> most GSM code uses. The decoding algorithm exploits the symmetric
> structure of the Viterbi add-compare-select (ACS) operation - commonly
> known as the ACS butterfly. This shift-register optimization can be
> found in the well-known text by Dave Forney.
>
> Forney, G.D., "The Viterbi Algorithm," Proc. of the IEEE, March 1973.
>
> Implementation is non-architecture specific and improves performance on
> x86 as well as ARM processors. Existing API is unchanged with optimized
> code being called internally for supported codes.
>
> Signed-off-by: Thomas Tsou <tom at tsou.cc>
> ---
> src/Makefile.am | 3 +-
> src/conv.c | 9 +
> src/viterbi.c | 603 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> src/viterbi_gen.c | 182 ++++++++++++++++
> 4 files changed, 796 insertions(+), 1 deletion(-)
> create mode 100644 src/viterbi.c
> create mode 100644 src/viterbi_gen.c
>
> diff --git a/src/Makefile.am b/src/Makefile.am
> index e68c29a..262a4e6 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -13,7 +13,8 @@ libosmocore_la_SOURCES = timer.c select.c signal.c msgb.c bits.c \
> logging.c logging_syslog.c rate_ctr.c \
> gsmtap_util.c crc16.c panic.c backtrace.c \
> conv.c application.c rbtree.c strrb.c \
> - loggingrb.c crc8gen.c crc16gen.c crc32gen.c crc64gen.c
> + loggingrb.c crc8gen.c crc16gen.c crc32gen.c crc64gen.c \
> + viterbi.c viterbi_gen.c
>
> BUILT_SOURCES = crc8gen.c crc16gen.c crc32gen.c crc64gen.c
>
> diff --git a/src/conv.c b/src/conv.c
> index f13deef..79b3a7c 100644
> --- a/src/conv.c
> +++ b/src/conv.c
> @@ -238,6 +238,11 @@ osmo_conv_encode(const struct osmo_conv_code *code,
>
> #define MAX_AE 0x00ffffff
>
> +/* Forward declaration for accerlated decoding with certain codes */
> +int
> +osmo_conv_decode_acc(const struct osmo_conv_code *code,
> + const sbit_t *input, ubit_t *output);
> +
> void
> osmo_conv_decode_init(struct osmo_conv_decoder *decoder,
> const struct osmo_conv_code *code, int len, int start_state)
> @@ -606,6 +611,10 @@ osmo_conv_decode(const struct osmo_conv_code *code,
> struct osmo_conv_decoder decoder;
> int rv, l;
>
> + /* Use accelerated implementation for supported codes */
> + if ((code->N <= 4) && ((code->K == 5) || (code->K == 7)))
> + return osmo_conv_decode_acc(code, input, output);
> +
> osmo_conv_decode_init(&decoder, code, 0, 0);
>
> if (code->term == CONV_TERM_TAIL_BITING) {
> diff --git a/src/viterbi.c b/src/viterbi.c
> new file mode 100644
> index 0000000..db8d5c8
> --- /dev/null
> +++ b/src/viterbi.c
> @@ -0,0 +1,603 @@
> +/*
> + * Viterbi decoder
> + * Copyright (C) 2013, 2014 Thomas Tsou <tom at tsou.cc>
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include "config.h"
> +
> +#include <stdlib.h>
> +#include <malloc.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <osmocom/core/conv.h>
> +
> +/* Forward Metric Units */
> +void gen_metrics_k5_n2(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +void gen_metrics_k5_n3(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +void gen_metrics_k5_n4(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +void gen_metrics_k7_n2(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +void gen_metrics_k7_n3(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +void gen_metrics_k7_n4(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm);
> +/* Trellis State
> + * state - Internal lshift register value
> + * prev - Register values of previous 0 and 1 states
> + */
> +struct vstate {
> + unsigned state;
> + unsigned prev[2];
> +};
> +
> +/* Trellis Object
> + * num_states - Number of states in the trellis
> + * sums - Accumulated path metrics
> + * outputs - Trellis ouput values
> + * vals - Input value that led to each state
> + */
> +struct vtrellis {
> + int num_states;
> + int16_t *sums;
> + int16_t *outputs;
> + uint8_t *vals;
> +};
> +
> +/* Viterbi Decoder
> + * n - Code order
> + * k - Constraint length
> + * len - Horizontal length of trellis
> + * recursive - Set to '1' if the code is recursive
> + * intrvl - Normalization interval
> + * trellis - Trellis object
> + * punc - Puncturing sequence
> + * paths - Trellis paths
> + */
> +struct vdecoder {
> + int n;
> + int k;
> + int len;
> + int recursive;
> + int intrvl;
> + struct vtrellis *trellis;
> + int *punc;
> + int16_t **paths;
> +
> + void (*metric_func)(const int8_t *, const int16_t *,
> + int16_t *, int16_t *, int);
> +};
> +
> +/* Aligned Memory Allocator
> + * SSE requires 16-byte memory alignment. We store relevant trellis values
> + * (accumulated sums, outputs, and path decisions) as 16 bit signed integers
> + * so the allocated memory is casted as such.
> + */
> +#define SSE_ALIGN 16
> +
> +static int16_t *vdec_malloc(size_t n)
> +{
> +#ifdef HAVE_SSE3
> + return (int16_t *) memalign(SSE_ALIGN, sizeof(int16_t) * n);
> +#else
> + return (int16_t *) malloc(sizeof(int16_t) * n);
> +#endif
> +}
> +
> +/* Accessor calls */
> +inline int conv_code_recursive(const struct osmo_conv_code *code)
> +{
> + return code->next_term_output ? 1 : 0;
> +}
> +
> +/* Left shift and mask for finding the previous state */
> +static unsigned vstate_lshift(unsigned reg, int k, int val)
> +{
> + unsigned mask;
> +
> + if (k == 5)
> + mask = 0x0e;
> + else if (k == 7)
> + mask = 0x3e;
> + else
> + mask = 0;
> +
> + return ((reg << 1) & mask) | val;
> +}
> +
> +/* Bit endian manipulators */
> +inline unsigned bitswap2(unsigned v)
> +{
> + return ((v & 0x02) >> 1) | ((v & 0x01) << 1);
> +}
> +
> +inline unsigned bitswap3(unsigned v)
> +{
> + return ((v & 0x04) >> 2) | ((v & 0x02) >> 0) |
> + ((v & 0x01) << 2);
> +}
> +
> +inline unsigned bitswap4(unsigned v)
> +{
> + return ((v & 0x08) >> 3) | ((v & 0x04) >> 1) |
> + ((v & 0x02) << 1) | ((v & 0x01) << 3);
> +}
> +
> +inline unsigned bitswap5(unsigned v)
> +{
> + return ((v & 0x10) >> 4) | ((v & 0x08) >> 2) | ((v & 0x04) >> 0) |
> + ((v & 0x02) << 2) | ((v & 0x01) << 4);
> +}
> +
> +inline unsigned bitswap6(unsigned v)
> +{
> + return ((v & 0x20) >> 5) | ((v & 0x10) >> 3) | ((v & 0x08) >> 1) |
> + ((v & 0x04) << 1) | ((v & 0x02) << 3) | ((v & 0x01) << 5);
> +}
> +
> +static unsigned bitswap(unsigned v, unsigned n)
> +{
> + switch (n) {
> + case 1:
> + return v;
> + case 2:
> + return bitswap2(v);
> + case 3:
> + return bitswap3(v);
> + case 4:
> + return bitswap4(v);
> + case 5:
> + return bitswap5(v);
> + case 6:
> + return bitswap6(v);
> + default:
> + break;
> + }
> +
> + return 0;
> +}
> +
> +/* Generate non-recursive state output from generator state table
> + * Note that the shift register moves right (i.e. the most recent bit is
> + * shifted into the register at k-1 bit of the register), which is typical
> + * textbook representation. The API transition table expects the most recent
> + * bit in the low order bit, or left shift. A bitswap operation is required
> + * to accommodate the difference.
> + */
> +static unsigned gen_output(struct vstate *state, int val,
> + const struct osmo_conv_code *code)
> +{
> + unsigned out, prev;
> +
> + prev = bitswap(state->prev[0], code->K - 1);
> + out = code->next_output[prev][val];
> + out = bitswap(out, code->N);
> +
> + return out;
> +}
> +
> +#define BIT2NRZ(REG,N) (((REG >> N) & 0x01) * 2 - 1) * -1
> +
> +/* Populate non-recursive trellis state
> + * For a given state defined by the k-1 length shift register, find the
> + * value of the input bit that drove the trellis to that state. Also
> + * generate the N outputs of the generator polynomial at that state.
> + */
> +static int gen_state_info(uint8_t *val, unsigned reg,
> + int16_t *output, const struct osmo_conv_code *code)
> +{
> + int i;
> + unsigned out;
> + struct vstate state;
> +
> + /* Previous '0' state */
> + state.state = reg;
> + state.prev[0] = vstate_lshift(reg, code->K, 0);
> + state.prev[1] = vstate_lshift(reg, code->K, 1);
> +
> + *val = (reg >> (code->K - 2)) & 0x01;
> +
> + /* Transition output */
> + out = gen_output(&state, *val, code);
> +
> + /* Unpack to NRZ */
> + for (i = 0; i < code->N; i++)
> + output[i] = BIT2NRZ(out, i);
> +
> + return 0;
> +}
> +
> +/* Generate recursive state output from generator state table */
> +static unsigned gen_recursive_output(struct vstate *state,
> + uint8_t *val, unsigned reg,
> + const struct osmo_conv_code *code, int pos)
> +{
> + int val0, val1;
> + unsigned out, prev;
> +
> + /* Previous '0' state */
> + prev = vstate_lshift(reg, code->K, 0);
> + prev = bitswap(prev, code->K - 1);
> +
> + /* Input value */
> + val0 = (reg >> (code->K - 2)) & 0x01;
> + val1 = (code->next_term_output[prev] >> pos) & 0x01;
> + *val = val0 == val1 ? 0 : 1;
> +
> + /* Wrapper for osmocom state access */
> + prev = bitswap(state->prev[0], code->K - 1);
> +
> + /* Compute the transition output */
> + out = code->next_output[prev][*val];
> + out = bitswap(out, code->N);
> +
> + return out;
> +}
> +
> +#define NUM_STATES(K) (K == 7 ? 64 : 16)
> +
> +/* Populate recursive trellis state
> + * The bit position of the systematic bit is not explicitly marked by the
> + * API, so it must be extracted from the generator table. Otherwise,
> + * populate the trellis similar to the non-recursive version.
> + * Non-systematic recursive codes are not supported.
> + */
> +static int gen_recursive_state_info(uint8_t *val,
> + unsigned reg,
> + int16_t *output,
> + const struct osmo_conv_code *code)
> +{
> + int i, j, pos = -1;
> + int ns = NUM_STATES(code->K);
> + unsigned out;
> + struct vstate state;
> +
> + /* Previous '0' and '1' states */
> + state.state = reg;
> + state.prev[0] = vstate_lshift(reg, code->K, 0);
> + state.prev[1] = vstate_lshift(reg, code->K, 1);
> +
> + /* Find recursive bit location */
> + for (i = 0; i < code->N; i++) {
> + for (j = 0; j < ns; j++) {
> + if ((code->next_output[j][0] >> i) & 0x01)
> + break;
> + }
> + if (j == ns) {
> + pos = i;
> + break;
> + }
> + }
> +
> + /* Non-systematic recursive code not supported */
> + if (pos < 0)
> + return -EPROTO;
> +
> + /* Transition output */
> + out = gen_recursive_output(&state, val, reg, code, pos);
> +
> + /* Unpack to NRZ */
> + for (i = 0; i < code->N; i++)
> + output[i] = BIT2NRZ(out, i);
> +
> + return 0;
> +}
> +
> +/* Release the trellis */
> +static void free_trellis(struct vtrellis *trellis)
> +{
> + if (!trellis)
> + return;
> +
> + free(trellis->vals);
> + free(trellis->outputs);
> + free(trellis->sums);
> + free(trellis);
> +}
> +
> +/* Allocate and initialize the trellis object
> + * Initialization consists of generating the outputs and output value of a
> + * given state. Due to trellis symmetry and anti-symmetry, only one of the
> + * transition paths is utilized by the butterfly operation in the forward
> + * recursion, so only one set of N outputs is required per state variable.
> + */
> +static struct vtrellis *generate_trellis(const struct osmo_conv_code *code)
> +{
> + int i, rc = -1;
> + struct vtrellis *trellis;
> + int16_t *outputs;
> +
> + int ns = NUM_STATES(code->K);
> + int recursive = conv_code_recursive(code);
> + int olen = (code->N == 2) ? 2 : 4;
> +
> + trellis = (struct vtrellis *) calloc(1, sizeof(struct vtrellis));
> + trellis->num_states = ns;
> + trellis->sums = vdec_malloc(ns);
> + trellis->outputs = vdec_malloc(ns * olen);
> + trellis->vals = (uint8_t *) malloc(ns * sizeof(uint8_t));
> +
> + if (!trellis->sums || !trellis->outputs)
> + goto fail;
> +
> + /* Populate the trellis state objects */
> + for (i = 0; i < ns; i++) {
> + outputs = &trellis->outputs[olen * i];
> +
> + if (recursive)
> + rc = gen_recursive_state_info(&trellis->vals[i],
> + i, outputs, code);
> + else
> + rc = gen_state_info(&trellis->vals[i],
> + i, outputs, code);
> + }
> +
> + if (rc < 0)
> + goto fail;
> +
> + return trellis;
> +fail:
> + free_trellis(trellis);
> + return NULL;
> +}
> +
> +/* Reset decoder
> + * Set accumulated path metrics to zero. For termination other than
> + * tail-biting, initialize the zero state as the encoder starting state.
> + * Intialize with the maximum accumulated sum at length equal to the
> + * constraint length.
> + */
> +static void reset_decoder(struct vdecoder *dec, int term)
> +{
> + int ns = dec->trellis->num_states;
> +
> + memset(dec->trellis->sums, 0, sizeof(int16_t) * ns);
> +
> + if (term != CONV_TERM_TAIL_BITING)
> + dec->trellis->sums[0] = INT8_MAX * dec->n * dec->k;
> +}
> +
> +static void _traceback(struct vdecoder *dec,
> + unsigned state, uint8_t *out, int len)
> +{
> + int i;
> + unsigned path;
> +
> + for (i = len - 1; i >= 0; i--) {
> + path = dec->paths[i][state] + 1;
> + out[i] = dec->trellis->vals[state];
> + state = vstate_lshift(state, dec->k, path);
> + }
> +}
> +
> +static void _traceback_rec(struct vdecoder *dec,
> + unsigned state, uint8_t *out, int len)
> +{
> + int i;
> + unsigned path;
> +
> + for (i = len - 1; i >= 0; i--) {
> + path = dec->paths[i][state] + 1;
> + out[i] = path ^ dec->trellis->vals[state];
> + state = vstate_lshift(state, dec->k, path);
> + }
> +}
> +
> +/* Traceback and generate decoded output
> + * Find the largest accumulated path metric at the final state except for
> + * the zero terminated case, where we assume the final state is always zero.
> + */
> +static int traceback(struct vdecoder *dec, uint8_t *out, int term, int len)
> +{
> + int i, sum, max = -1;
> + unsigned path, state = 0;
> +
> + if (term != CONV_TERM_FLUSH) {
> + for (i = 0; i < dec->trellis->num_states; i++) {
> + sum = dec->trellis->sums[i];
> + if (sum > max) {
> + max = sum;
> + state = i;
> + }
> + }
> +
> + if (max < 0)
> + return -EPROTO;
> + }
> +
> + for (i = dec->len - 1; i >= len; i--) {
> + path = dec->paths[i][state] + 1;
> + state = vstate_lshift(state, dec->k, path);
> + }
> +
> + if (dec->recursive)
> + _traceback_rec(dec, state, out, len);
> + else
> + _traceback(dec, state, out, len);
> +
> + return 0;
> +}
> +
> +/* Release decoder object */
> +static void free_vdec(struct vdecoder *dec)
> +{
> + if (!dec)
> + return;
> +
> + free(dec->paths[0]);
> + free(dec->paths);
> + free_trellis(dec->trellis);
> + free(dec);
> +}
> +
> +/* Allocate decoder object
> + * Subtract the constraint length K on the normalization interval to
> + * accommodate the initialization path metric at state zero.
> + */
> +static struct vdecoder *alloc_vdec(const struct osmo_conv_code *code)
> +{
> + int i, ns;
> + struct vdecoder *dec;
> +
> + ns = NUM_STATES(code->K);
> +
> + dec = (struct vdecoder *) calloc(1, sizeof(struct vdecoder));
> + dec->n = code->N;
> + dec->k = code->K;
> + dec->recursive = conv_code_recursive(code);
> + dec->intrvl = INT16_MAX / (dec->n * INT8_MAX) - dec->k;
> +
> + if (dec->k == 5) {
> + switch (dec->n) {
> + case 2:
> + dec->metric_func = gen_metrics_k5_n2;
> + break;
> + case 3:
> + dec->metric_func = gen_metrics_k5_n3;
> + break;
> + case 4:
> + dec->metric_func = gen_metrics_k5_n4;
> + break;
> + default:
> + goto fail;
> + }
> + } else if (dec->k == 7) {
> + switch (dec->n) {
> + case 2:
> + dec->metric_func = gen_metrics_k7_n2;
> + break;
> + case 3:
> + dec->metric_func = gen_metrics_k7_n3;
> + break;
> + case 4:
> + dec->metric_func = gen_metrics_k7_n4;
> + break;
> + default:
> + goto fail;
> + }
> + } else {
> + goto fail;
> + }
> +
> + if (code->term == CONV_TERM_FLUSH)
> + dec->len = code->len + code->K - 1;
> + else
> + dec->len = code->len;
> +
> + dec->trellis = generate_trellis(code);
> + if (!dec->trellis)
> + goto fail;
> +
> + dec->paths = (int16_t **) malloc(sizeof(int16_t *) * dec->len);
> + dec->paths[0] = vdec_malloc(ns * dec->len);
> + for (i = 1; i < dec->len; i++)
> + dec->paths[i] = &dec->paths[0][i * ns];
> +
> + return dec;
> +fail:
> + free_vdec(dec);
> + return NULL;
> +}
> +
> +/* Depuncture sequence with nagative value terminated puncturing matrix */
> +static int depuncture(const int8_t *in, const int *punc, int8_t *out, int len)
> +{
> + int i, n = 0, m = 0;
> +
> + for (i = 0; i < len; i++) {
> + if (i == punc[n]) {
> + out[i] = 0;
> + n++;
> + continue;
> + }
> +
> + out[i] = in[m++];
> + }
> +
> + return 0;
> +}
> +
> +/* Forward trellis recursion
> + * Generate branch metrics and path metrics with a combined function. Only
> + * accumulated path metric sums and path selections are stored. Normalize on
> + * the interval specified by the decoder.
> + */
> +static void _conv_decode(struct vdecoder *dec, const int8_t *seq, int _cnt)
> +{
> + int i, len = dec->len;
> + struct vtrellis *trellis = dec->trellis;
> +
> + for (i = 0; i < len; i++) {
> + dec->metric_func(&seq[dec->n * i],
> + trellis->outputs,
> + trellis->sums,
> + dec->paths[i],
> + !(i % dec->intrvl));
> + }
> +}
> +
> +/* Convolutional decode with a decoder object
> + * Initial puncturing run if necessary followed by the forward recursion.
> + * For tail-biting perform a second pass before running the backward
> + * traceback operation.
> + */
> +static int conv_decode(struct vdecoder *dec, const int8_t *seq,
> + const int *punc, uint8_t *out, int len, int term)
> +{
> + int cnt = 0;
> + int8_t depunc[dec->len * dec->n];
> +
> + reset_decoder(dec, term);
> +
> + if (punc) {
> + depuncture(seq, punc, depunc, dec->len * dec->n);
> + seq = depunc;
> + }
> +
> + /* Propagate through the trellis with interval normalization */
> + _conv_decode(dec, seq, cnt);
> +
> + if (term == CONV_TERM_TAIL_BITING)
> + _conv_decode(dec, seq, cnt);
> +
> + return traceback(dec, out, term, len);
> +}
> +
> +/* All-in-one viterbi decoding */
> +int osmo_conv_decode_acc(const struct osmo_conv_code *code,
> + const sbit_t *input, ubit_t *output)
> +{
> + int rc;
> + struct vdecoder *vdec;
> +
> + if ((code->N < 2) || (code->N > 4) || (code->len < 1) ||
> + ((code->K != 5) && (code->K != 7)))
> + return -EINVAL;
> +
> + vdec = alloc_vdec(code);
> + if (!vdec)
> + return -EFAULT;
> +
> + rc = conv_decode(vdec, input, code->puncture,
> + output, code->len, code->term);
> +
> + free_vdec(vdec);
> +
> + return rc;
> +}
> diff --git a/src/viterbi_gen.c b/src/viterbi_gen.c
> new file mode 100644
> index 0000000..894d5ae
> --- /dev/null
> +++ b/src/viterbi_gen.c
> @@ -0,0 +1,182 @@
> +/*
> + * Viterbi decoder
> + * Copyright (C) 2013, 2014 Thomas Tsou <tom at tsou.cc>
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <stdint.h>
> +#include <string.h>
> +
> +/* Add-Compare-Select (ACS-Butterfly)
> + * Compute 4 accumulated path metrics and 4 path selections. Note that path
> + * selections are store as -1 and 0 rather than 0 and 1. This is to match
> + * the output format of the SSE packed compare instruction 'pmaxuw'.
> + */
> +void acs_butterfly(int state, int num_states,
> + int16_t metric, int16_t *sum,
> + int16_t *new_sum, int16_t *path)
> +{
> + int state0, state1;
> + int sum0, sum1, sum2, sum3;
> +
> + state0 = *(sum + (2 * state + 0));
> + state1 = *(sum + (2 * state + 1));
> +
> + sum0 = state0 + metric;
> + sum1 = state1 - metric;
> + sum2 = state0 - metric;
> + sum3 = state1 + metric;
> +
> + if (sum0 > sum1) {
> + *new_sum = sum0;
> + *path = -1;
> + } else {
> + *new_sum = sum1;
> + *path = 0;
> + }
> +
> + if (sum2 > sum3) {
> + *(new_sum + num_states / 2) = sum2;
> + *(path + num_states / 2) = -1;
> + } else {
> + *(new_sum + num_states / 2) = sum3;
> + *(path + num_states / 2) = 0;
> + }
> +}
> +
> +/* Branch metrics unit N=2 */
> +void _gen_branch_metrics_n2(int num_states, const int8_t *seq,
> + const int16_t *out, int16_t *metrics)
> +{
> + int i;
> +
> + for (i = 0; i < num_states / 2; i++) {
> + metrics[i] = seq[0] * out[2 * i + 0] +
> + seq[1] * out[2 * i + 1];
> + }
> +}
> +
> +/* Branch metrics unit N=3 */
> +void _gen_branch_metrics_n3(int num_states, const int8_t *seq,
> + const int16_t *out, int16_t *metrics)
> +{
> + int i;
> +
> + for (i = 0; i < num_states / 2; i++)
> + metrics[i] = seq[0] * out[4 * i + 0] +
> + seq[1] * out[4 * i + 1] +
> + seq[2] * out[4 * i + 2];
> +}
> +
> +/* Branch metrics unit N=4 */
> +void _gen_branch_metrics_n4(int num_states, const int8_t *seq,
> + const int16_t *out, int16_t *metrics)
> +{
> + int i;
> +
> + for (i = 0; i < num_states / 2; i++)
> + metrics[i] = seq[0] * out[4 * i + 0] +
> + seq[1] * out[4 * i + 1] +
> + seq[2] * out[4 * i + 2] +
> + seq[3] * out[4 * i + 3];
> +}
> +
> +/* Path metric unit */
> +void _gen_path_metrics(int num_states, int16_t *sums,
> + int16_t *metrics, int16_t *paths, int norm)
> +{
> + int i;
> + int16_t min;
> + int16_t new_sums[num_states];
> +
> + for (i = 0; i < num_states / 2; i++) {
> + acs_butterfly(i, num_states, metrics[i],
> + sums, &new_sums[i], &paths[i]);
> + }
> +
> + if (norm) {
> + min = new_sums[0];
> + for (i = 1; i < num_states; i++) {
> + if (new_sums[i] < min)
> + min = new_sums[i];
> + }
> +
> + for (i = 0; i < num_states; i++)
> + new_sums[i] -= min;
> + }
> +
> + memcpy(sums, new_sums, num_states * sizeof(int16_t));
> +}
> +
> +/* 16-state branch-path metrics units (K=5) */
> +void gen_metrics_k5_n2(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[8];
> +
> + _gen_branch_metrics_n2(16, seq, out, metrics);
> + _gen_path_metrics(16, sums, metrics, paths, norm);
> +}
> +
> +void gen_metrics_k5_n3(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[8];
> +
> + _gen_branch_metrics_n3(16, seq, out, metrics);
> + _gen_path_metrics(16, sums, metrics, paths, norm);
> +
> +}
> +
> +void gen_metrics_k5_n4(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[8];
> +
> + _gen_branch_metrics_n4(16, seq, out, metrics);
> + _gen_path_metrics(16, sums, metrics, paths, norm);
> +
> +}
> +
> +/* 64-state branch-path metrics units (K=7) */
> +void gen_metrics_k7_n2(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[32];
> +
> + _gen_branch_metrics_n2(64, seq, out, metrics);
> + _gen_path_metrics(64, sums, metrics, paths, norm);
> +
> +}
> +
> +void gen_metrics_k7_n3(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[32];
> +
> + _gen_branch_metrics_n3(64, seq, out, metrics);
> + _gen_path_metrics(64, sums, metrics, paths, norm);
> +
> +}
> +
> +void gen_metrics_k7_n4(const int8_t *seq, const int16_t *out,
> + int16_t *sums, int16_t *paths, int norm)
> +{
> + int16_t metrics[32];
> +
> + _gen_branch_metrics_n4(64, seq, out, metrics);
> + _gen_path_metrics(64, sums, metrics, paths, norm);
> +}
> --
> 1.9.0
>