Bill Yi | 4e213d5 | 2015-06-23 13:53:11 -0700 | [diff] [blame] | 1 | /* K=15 r=1/6 Viterbi decoder for x86 SSE2 |
| 2 | * Copyright Mar 2004, Phil Karn, KA9Q |
| 3 | * May be used under the terms of the GNU Lesser General Public License (LGPL) |
| 4 | */ |
| 5 | #include <emmintrin.h> |
| 6 | #include <stdio.h> |
| 7 | #include <stdlib.h> |
| 8 | #include <memory.h> |
| 9 | #include <limits.h> |
| 10 | #include "fec.h" |
| 11 | |
| 12 | typedef union { unsigned long w[512]; unsigned short s[1024];} decision_t; |
| 13 | typedef union { signed short s[16384]; __m128i v[2048];} metric_t; |
| 14 | |
| 15 | static union branchtab615 { unsigned short s[8192]; __m128i v[1024];} Branchtab615[6]; |
| 16 | static int Init = 0; |
| 17 | |
| 18 | /* State info for instance of Viterbi decoder */ |
| 19 | struct v615 { |
| 20 | metric_t metrics1; /* path metric buffer 1 */ |
| 21 | metric_t metrics2; /* path metric buffer 2 */ |
| 22 | void *dp; /* Pointer to current decision */ |
| 23 | metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ |
| 24 | void *decisions; /* Beginning of decisions for block */ |
| 25 | }; |
| 26 | |
| 27 | /* Initialize Viterbi decoder for start of new frame */ |
| 28 | int init_viterbi615_sse2(void *p,int starting_state){ |
| 29 | struct v615 *vp = p; |
| 30 | int i; |
| 31 | |
| 32 | if(p == NULL) |
| 33 | return -1; |
| 34 | for(i=0;i<16384;i++) |
| 35 | vp->metrics1.s[i] = (SHRT_MIN+5000); |
| 36 | |
| 37 | vp->old_metrics = &vp->metrics1; |
| 38 | vp->new_metrics = &vp->metrics2; |
| 39 | vp->dp = vp->decisions; |
| 40 | vp->old_metrics->s[starting_state & 16383] = SHRT_MIN; /* Bias known start state */ |
| 41 | return 0; |
| 42 | } |
| 43 | |
| 44 | /* Create a new instance of a Viterbi decoder */ |
| 45 | void *create_viterbi615_sse2(int len){ |
| 46 | void *p; |
| 47 | struct v615 *vp; |
| 48 | |
| 49 | if(!Init){ |
| 50 | int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF }; |
| 51 | set_viterbi615_polynomial_sse2(polys); |
| 52 | } |
| 53 | |
| 54 | /* Ordinary malloc() only returns 8-byte alignment, we need 16 */ |
| 55 | if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v615))) |
| 56 | return NULL; |
| 57 | |
| 58 | vp = (struct v615 *)p; |
| 59 | if((p = malloc((len+14)*sizeof(decision_t))) == NULL){ |
| 60 | free(vp); |
| 61 | return NULL; |
| 62 | } |
| 63 | vp->decisions = (decision_t *)p; |
| 64 | init_viterbi615_sse2(vp,0); |
| 65 | return vp; |
| 66 | } |
| 67 | |
| 68 | void set_viterbi615_polynomial_sse2(int polys[6]){ |
| 69 | int state; |
| 70 | int i; |
| 71 | |
| 72 | for(state=0;state < 8192;state++){ |
| 73 | for(i=0;i<6;i++) |
| 74 | Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0; |
| 75 | } |
| 76 | Init++; |
| 77 | } |
| 78 | |
| 79 | /* Viterbi chainback */ |
| 80 | int chainback_viterbi615_sse2( |
| 81 | void *p, |
| 82 | unsigned char *data, /* Decoded output data */ |
| 83 | unsigned int nbits, /* Number of data bits */ |
| 84 | unsigned int endstate){ /* Terminal encoder state */ |
| 85 | struct v615 *vp = p; |
| 86 | decision_t *d = (decision_t *)vp->decisions; |
| 87 | |
| 88 | endstate %= 16384; |
| 89 | |
| 90 | /* The store into data[] only needs to be done every 8 bits. |
| 91 | * But this avoids a conditional branch, and the writes will |
| 92 | * combine in the cache anyway |
| 93 | */ |
| 94 | d += 14; /* Look past tail */ |
| 95 | while(nbits-- != 0){ |
| 96 | int k; |
| 97 | |
| 98 | k = (d[nbits].w[endstate/32] >> (endstate%32)) & 1; |
| 99 | endstate = (k << 13) | (endstate >> 1); |
| 100 | data[nbits>>3] = endstate >> 6; |
| 101 | } |
| 102 | return 0; |
| 103 | } |
| 104 | |
| 105 | /* Delete instance of a Viterbi decoder */ |
| 106 | void delete_viterbi615_sse2(void *p){ |
| 107 | struct v615 *vp = p; |
| 108 | |
| 109 | if(vp != NULL){ |
| 110 | free(vp->decisions); |
| 111 | free(vp); |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | |
| 116 | int update_viterbi615_blk_sse2(void *p,unsigned char *syms,int nbits){ |
| 117 | struct v615 *vp = p; |
| 118 | decision_t *d = (decision_t *)vp->dp; |
| 119 | |
| 120 | while(nbits--){ |
| 121 | __m128i sym0v,sym1v,sym2v,sym3v,sym4v,sym5v; |
| 122 | void *tmp; |
| 123 | int i; |
| 124 | |
| 125 | /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */ |
| 126 | sym0v = _mm_set1_epi16(syms[0]); |
| 127 | sym1v = _mm_set1_epi16(syms[1]); |
| 128 | sym2v = _mm_set1_epi16(syms[2]); |
| 129 | sym3v = _mm_set1_epi16(syms[3]); |
| 130 | sym4v = _mm_set1_epi16(syms[4]); |
| 131 | sym5v = _mm_set1_epi16(syms[5]); |
| 132 | syms += 6; |
| 133 | |
| 134 | /* SSE2 doesn't support saturated adds on unsigned shorts, so we have to use signed shorts */ |
| 135 | for(i=0;i<1024;i++){ |
| 136 | __m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1; |
| 137 | |
| 138 | /* Form branch metrics |
| 139 | * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255, |
| 140 | * the XOR operations constitute conditional negation. |
| 141 | * metric and m_metric (-metric) are in the range 0-1530 |
| 142 | */ |
| 143 | m0 = _mm_add_epi16(_mm_xor_si128(Branchtab615[0].v[i],sym0v),_mm_xor_si128(Branchtab615[1].v[i],sym1v)); |
| 144 | m1 = _mm_add_epi16(_mm_xor_si128(Branchtab615[2].v[i],sym2v),_mm_xor_si128(Branchtab615[3].v[i],sym3v)); |
| 145 | m2 = _mm_add_epi16(_mm_xor_si128(Branchtab615[4].v[i],sym4v),_mm_xor_si128(Branchtab615[5].v[i],sym5v)); |
| 146 | metric = _mm_add_epi16(m0,_mm_add_epi16(m1,m2)); |
| 147 | m_metric = _mm_sub_epi16(_mm_set1_epi16(1530),metric); |
| 148 | |
| 149 | /* Add branch metrics to path metrics */ |
| 150 | m0 = _mm_adds_epi16(vp->old_metrics->v[i],metric); |
| 151 | m3 = _mm_adds_epi16(vp->old_metrics->v[1024+i],metric); |
| 152 | m1 = _mm_adds_epi16(vp->old_metrics->v[1024+i],m_metric); |
| 153 | m2 = _mm_adds_epi16(vp->old_metrics->v[i],m_metric); |
| 154 | |
| 155 | /* Compare and select */ |
| 156 | survivor0 = _mm_min_epi16(m0,m1); |
| 157 | survivor1 = _mm_min_epi16(m2,m3); |
| 158 | decision0 = _mm_cmpeq_epi16(survivor0,m1); |
| 159 | decision1 = _mm_cmpeq_epi16(survivor1,m3); |
| 160 | |
| 161 | /* Pack each set of decisions into 8 8-bit bytes, then interleave them and compress into 16 bits */ |
| 162 | d->s[i] = _mm_movemask_epi8(_mm_unpacklo_epi8(_mm_packs_epi16(decision0,_mm_setzero_si128()),_mm_packs_epi16(decision1,_mm_setzero_si128()))); |
| 163 | |
| 164 | /* Store surviving metrics */ |
| 165 | vp->new_metrics->v[2*i] = _mm_unpacklo_epi16(survivor0,survivor1); |
| 166 | vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi16(survivor0,survivor1); |
| 167 | } |
| 168 | /* See if we need to renormalize |
| 169 | * Max metric spread for this code with 0-90 branch metrics is 405 |
| 170 | */ |
| 171 | if(vp->new_metrics->s[0] >= SHRT_MAX-12750){ |
| 172 | int i,adjust; |
| 173 | __m128i adjustv; |
| 174 | union { __m128i v; signed short w[8]; } t; |
| 175 | |
| 176 | /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */ |
| 177 | adjustv = vp->new_metrics->v[0]; |
| 178 | for(i=1;i<2048;i++) |
| 179 | adjustv = _mm_min_epi16(adjustv,vp->new_metrics->v[i]); |
| 180 | |
| 181 | adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,8)); |
| 182 | adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,4)); |
| 183 | adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,2)); |
| 184 | t.v = adjustv; |
| 185 | adjust = t.w[0] - SHRT_MIN; |
| 186 | adjustv = _mm_set1_epi16(adjust); |
| 187 | |
| 188 | /* We cannot use a saturated subtract, because we often have to adjust by more than SHRT_MAX |
| 189 | * This is okay since it can't overflow anyway |
| 190 | */ |
| 191 | for(i=0;i<2048;i++) |
| 192 | vp->new_metrics->v[i] = _mm_sub_epi16(vp->new_metrics->v[i],adjustv); |
| 193 | } |
| 194 | d++; |
| 195 | /* Swap pointers to old and new metrics */ |
| 196 | tmp = vp->old_metrics; |
| 197 | vp->old_metrics = vp->new_metrics; |
| 198 | vp->new_metrics = tmp; |
| 199 | } |
| 200 | vp->dp = d; |
| 201 | return 0; |
| 202 | } |
| 203 | |
| 204 | |