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 } 203 204 205
