Tom Tsou | 3553680 | 2016-11-24 19:24:32 +0700 | [diff] [blame] | 1 | /* |
| 2 | * Viterbi decoder |
| 3 | * |
| 4 | * Copyright (C) 2013, 2014 Thomas Tsou <tom@tsou.cc> |
| 5 | * |
| 6 | * All Rights Reserved |
| 7 | * |
| 8 | * This program is free software; you can redistribute it and/or modify |
| 9 | * it under the terms of the GNU General Public License as published by |
| 10 | * the Free Software Foundation; either version 2 of the License, or |
| 11 | * (at your option) any later version. |
| 12 | * |
| 13 | * This program is distributed in the hope that it will be useful, |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 16 | * GNU General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU General Public License along |
| 19 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 20 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 21 | */ |
| 22 | |
| 23 | #include <stdint.h> |
| 24 | #include <string.h> |
| 25 | |
| 26 | /* Add-Compare-Select (ACS-Butterfly) |
| 27 | * Compute 4 accumulated path metrics and 4 path selections. Note that path |
| 28 | * selections are store as -1 and 0 rather than 0 and 1. This is to match |
| 29 | * the output format of the SSE packed compare instruction 'pmaxuw'. |
| 30 | */ |
| 31 | |
| 32 | static void acs_butterfly(int state, int num_states, |
| 33 | int16_t metric, int16_t *sum, |
| 34 | int16_t *new_sum, int16_t *path) |
| 35 | { |
| 36 | int state0, state1; |
| 37 | int sum0, sum1, sum2, sum3; |
| 38 | |
| 39 | state0 = *(sum + (2 * state + 0)); |
| 40 | state1 = *(sum + (2 * state + 1)); |
| 41 | |
| 42 | sum0 = state0 + metric; |
| 43 | sum1 = state1 - metric; |
| 44 | sum2 = state0 - metric; |
| 45 | sum3 = state1 + metric; |
| 46 | |
| 47 | if (sum0 >= sum1) { |
| 48 | *new_sum = sum0; |
| 49 | *path = -1; |
| 50 | } else { |
| 51 | *new_sum = sum1; |
| 52 | *path = 0; |
| 53 | } |
| 54 | |
| 55 | if (sum2 >= sum3) { |
| 56 | *(new_sum + num_states / 2) = sum2; |
| 57 | *(path + num_states / 2) = -1; |
| 58 | } else { |
| 59 | *(new_sum + num_states / 2) = sum3; |
| 60 | *(path + num_states / 2) = 0; |
| 61 | } |
| 62 | } |
| 63 | |
| 64 | /* Branch metrics unit N=2 */ |
| 65 | static void gen_branch_metrics_n2(int num_states, const int8_t *seq, |
| 66 | const int16_t *out, int16_t *metrics) |
| 67 | { |
| 68 | int i; |
| 69 | |
| 70 | for (i = 0; i < num_states / 2; i++) { |
| 71 | metrics[i] = seq[0] * out[2 * i + 0] + |
| 72 | seq[1] * out[2 * i + 1]; |
| 73 | } |
| 74 | } |
| 75 | |
| 76 | /* Branch metrics unit N=3 */ |
| 77 | static void gen_branch_metrics_n3(int num_states, const int8_t *seq, |
| 78 | const int16_t *out, int16_t *metrics) |
| 79 | { |
| 80 | int i; |
| 81 | |
| 82 | for (i = 0; i < num_states / 2; i++) { |
| 83 | metrics[i] = seq[0] * out[4 * i + 0] + |
| 84 | seq[1] * out[4 * i + 1] + |
| 85 | seq[2] * out[4 * i + 2]; |
| 86 | } |
| 87 | } |
| 88 | |
| 89 | /* Branch metrics unit N=4 */ |
| 90 | static void gen_branch_metrics_n4(int num_states, const int8_t *seq, |
| 91 | const int16_t *out, int16_t *metrics) |
| 92 | { |
| 93 | int i; |
| 94 | |
| 95 | for (i = 0; i < num_states / 2; i++) { |
| 96 | metrics[i] = seq[0] * out[4 * i + 0] + |
| 97 | seq[1] * out[4 * i + 1] + |
| 98 | seq[2] * out[4 * i + 2] + |
| 99 | seq[3] * out[4 * i + 3]; |
| 100 | } |
| 101 | } |
| 102 | |
| 103 | /* Path metric unit */ |
| 104 | static void gen_path_metrics(int num_states, int16_t *sums, |
| 105 | int16_t *metrics, int16_t *paths, int norm) |
| 106 | { |
| 107 | int i; |
| 108 | int16_t min; |
| 109 | int16_t new_sums[num_states]; |
| 110 | |
| 111 | for (i = 0; i < num_states / 2; i++) |
| 112 | acs_butterfly(i, num_states, metrics[i], |
| 113 | sums, &new_sums[i], &paths[i]); |
| 114 | |
| 115 | if (norm) { |
| 116 | min = new_sums[0]; |
| 117 | |
| 118 | for (i = 1; i < num_states; i++) |
| 119 | if (new_sums[i] < min) |
| 120 | min = new_sums[i]; |
| 121 | |
| 122 | for (i = 0; i < num_states; i++) |
| 123 | new_sums[i] -= min; |
| 124 | } |
| 125 | |
| 126 | memcpy(sums, new_sums, num_states * sizeof(int16_t)); |
| 127 | } |
| 128 | |
| 129 | /* 16-state branch-path metrics units (K=5) */ |
| 130 | __attribute__ ((visibility("hidden"))) |
| 131 | void osmo_conv_gen_metrics_k5_n2(const int8_t *seq, const int16_t *out, |
| 132 | int16_t *sums, int16_t *paths, int norm) |
| 133 | { |
| 134 | int16_t metrics[8]; |
| 135 | |
| 136 | gen_branch_metrics_n2(16, seq, out, metrics); |
| 137 | gen_path_metrics(16, sums, metrics, paths, norm); |
| 138 | } |
| 139 | |
| 140 | __attribute__ ((visibility("hidden"))) |
| 141 | void osmo_conv_gen_metrics_k5_n3(const int8_t *seq, const int16_t *out, |
| 142 | int16_t *sums, int16_t *paths, int norm) |
| 143 | { |
| 144 | int16_t metrics[8]; |
| 145 | |
| 146 | gen_branch_metrics_n3(16, seq, out, metrics); |
| 147 | gen_path_metrics(16, sums, metrics, paths, norm); |
| 148 | |
| 149 | } |
| 150 | |
| 151 | __attribute__ ((visibility("hidden"))) |
| 152 | void osmo_conv_gen_metrics_k5_n4(const int8_t *seq, const int16_t *out, |
| 153 | int16_t *sums, int16_t *paths, int norm) |
| 154 | { |
| 155 | int16_t metrics[8]; |
| 156 | |
| 157 | gen_branch_metrics_n4(16, seq, out, metrics); |
| 158 | gen_path_metrics(16, sums, metrics, paths, norm); |
| 159 | |
| 160 | } |
| 161 | |
| 162 | /* 64-state branch-path metrics units (K=7) */ |
| 163 | __attribute__ ((visibility("hidden"))) |
| 164 | void osmo_conv_gen_metrics_k7_n2(const int8_t *seq, const int16_t *out, |
| 165 | int16_t *sums, int16_t *paths, int norm) |
| 166 | { |
| 167 | int16_t metrics[32]; |
| 168 | |
| 169 | gen_branch_metrics_n2(64, seq, out, metrics); |
| 170 | gen_path_metrics(64, sums, metrics, paths, norm); |
| 171 | |
| 172 | } |
| 173 | |
| 174 | __attribute__ ((visibility("hidden"))) |
| 175 | void osmo_conv_gen_metrics_k7_n3(const int8_t *seq, const int16_t *out, |
| 176 | int16_t *sums, int16_t *paths, int norm) |
| 177 | { |
| 178 | int16_t metrics[32]; |
| 179 | |
| 180 | gen_branch_metrics_n3(64, seq, out, metrics); |
| 181 | gen_path_metrics(64, sums, metrics, paths, norm); |
| 182 | |
| 183 | } |
| 184 | |
| 185 | __attribute__ ((visibility("hidden"))) |
| 186 | void osmo_conv_gen_metrics_k7_n4(const int8_t *seq, const int16_t *out, |
| 187 | int16_t *sums, int16_t *paths, int norm) |
| 188 | { |
| 189 | int16_t metrics[32]; |
| 190 | |
| 191 | gen_branch_metrics_n4(64, seq, out, metrics); |
| 192 | gen_path_metrics(64, sums, metrics, paths, norm); |
| 193 | } |