1 /* K=9 r=1/3 Viterbi decoder for x86 SSE 2 * Copyright Aug 2006, Phil Karn, KA9Q 3 * May be used under the terms of the GNU Lesser General Public License (LGPL) 4 */ 5 #include <xmmintrin.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[8]; unsigned char c[32];} decision_t; 13 typedef union { signed short s[256]; __m64 v[64];} metric_t; 14 15 static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3]; 16 static int Init = 0; 17 18 /* State info for instance of Viterbi decoder */ 19 struct v39 { 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_viterbi39_sse(void *p,int starting_state){ 29 struct v39 *vp = p; 30 int i; 31 32 if(p == NULL) 33 return -1; 34 for(i=0;i<256;i++) 35 vp->metrics1.s[i] = (SHRT_MIN+1000); 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 & 255] = SHRT_MIN; /* Bias known start state */ 41 return 0; 42 } 43 44 /* Create a new instance of a Viterbi decoder */ 45 void *create_viterbi39_sse(int len){ 46 struct v39 *vp; 47 48 if(!Init){ 49 int polys[3] = { V39POLYA, V39POLYB, V39POLYC }; 50 51 set_viterbi39_polynomial_sse(polys); 52 } 53 if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL){ 54 return NULL; 55 } 56 if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){ 57 free(vp); 58 return NULL; 59 } 60 init_viterbi39_sse(vp,0); 61 return vp; 62 } 63 64 void set_viterbi39_polynomial_sse(int polys[3]){ 65 int state; 66 67 for(state=0;state < 128;state++){ 68 Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0; 69 Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0; 70 Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0; 71 } 72 Init++; 73 } 74 75 /* Viterbi chainback */ 76 int chainback_viterbi39_sse( 77 void *p, 78 unsigned char *data, /* Decoded output data */ 79 unsigned int nbits, /* Number of data bits */ 80 unsigned int endstate){ /* Terminal encoder state */ 81 struct v39 *vp = p; 82 decision_t *d; 83 int path_metric; 84 85 if(p == NULL) 86 return -1; 87 d = (decision_t *)vp->decisions; 88 endstate %= 256; 89 90 path_metric = vp->old_metrics->s[endstate]; 91 92 /* The store into data[] only needs to be done every 8 bits. 93 * But this avoids a conditional branch, and the writes will 94 * combine in the cache anyway 95 */ 96 d += 8; /* Look past tail */ 97 while(nbits-- != 0){ 98 int k; 99 100 /* k = (d[nbits].w[endstate/32] >> (endstate%32)) & 1;*/ 101 k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1; 102 endstate = (k << 7) | (endstate >> 1); 103 data[nbits>>3] = endstate; 104 } 105 return path_metric - SHRT_MIN; 106 } 107 108 /* Delete instance of a Viterbi decoder */ 109 void delete_viterbi39_sse(void *p){ 110 struct v39 *vp = p; 111 112 if(vp != NULL){ 113 free(vp->decisions); 114 free(vp); 115 } 116 } 117 118 119 int update_viterbi39_blk_sse(void *p,unsigned char *syms,int nbits){ 120 struct v39 *vp = p; 121 decision_t *d; 122 int path_metric = 0; 123 124 if(p == NULL) 125 return -1; 126 d = (decision_t *)vp->dp; 127 while(nbits--){ 128 __m64 sym0v,sym1v,sym2v; 129 void *tmp; 130 int i; 131 132 /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */ 133 sym0v = _mm_set1_pi16(syms[0]); 134 sym1v = _mm_set1_pi16(syms[1]); 135 sym2v = _mm_set1_pi16(syms[2]); 136 syms += 3; 137 138 for(i=0;i<32;i++){ 139 __m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1; 140 141 /* Form branch metrics 142 * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255, 143 * the XOR operations constitute conditional negation. 144 * metric and m_metric (-metric) are in the range 0-765 145 */ 146 m0 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v)); 147 metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0); 148 m_metric = _mm_sub_pi16(_mm_set1_pi16(765),metric); 149 150 /* Add branch metrics to path metrics */ 151 m0 = _mm_adds_pi16(vp->old_metrics->v[i],metric); 152 m3 = _mm_adds_pi16(vp->old_metrics->v[32+i],metric); 153 m1 = _mm_adds_pi16(vp->old_metrics->v[32+i],m_metric); 154 m2 = _mm_adds_pi16(vp->old_metrics->v[i],m_metric); 155 156 /* Compare and select */ 157 survivor0 = _mm_min_pi16(m0,m1); 158 survivor1 = _mm_min_pi16(m2,m3); 159 decision0 = _mm_cmpeq_pi16(survivor0,m1); 160 decision1 = _mm_cmpeq_pi16(survivor1,m3); 161 162 /* Pack decisions into 8 bits and store */ 163 d->c[i] = _mm_movemask_pi8(_mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64()))); 164 165 /* Store surviving metrics */ 166 vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1); 167 vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1); 168 } 169 /* See if we need to renormalize 170 * Max metric spread for this code with 0-255 branch metrics is 12750 171 */ 172 if(vp->new_metrics->s[0] >= SHRT_MAX-5000){ 173 int i,adjust; 174 __m64 adjustv; 175 union { __m64 v; signed short w[4]; } t; 176 177 /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */ 178 adjustv = vp->new_metrics->v[0]; 179 for(i=1;i<64;i++) 180 adjustv = _mm_min_pi16(adjustv,vp->new_metrics->v[i]); 181 182 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,32)); 183 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,16)); 184 t.v = adjustv; 185 adjust = t.w[0] - SHRT_MIN; 186 path_metric += adjust; 187 adjustv = _mm_set1_pi16(adjust); 188 189 for(i=0;i<64;i++) 190 vp->new_metrics->v[i] = _mm_sub_pi16(vp->new_metrics->v[i],adjustv); 191 } 192 d++; 193 /* Swap pointers to old and new metrics */ 194 tmp = vp->old_metrics; 195 vp->old_metrics = vp->new_metrics; 196 vp->new_metrics = tmp; 197 } 198 vp->dp = d; 199 _mm_empty(); 200 return path_metric; 201 } 202
