1 /* K=15 r=1/6 Viterbi decoder for x86 MMX 2 * Mar 2004, Phil Karn, KA9Q 3 * May be used under the terms of the GNU Lesser General Public License (LGPL) 4 */ 5 #include <mmintrin.h> 6 #include <stdio.h> 7 #include <stdlib.h> 8 #include <memory.h> 9 #include "fec.h" 10 11 typedef union { unsigned char c[16384]; __m64 v[2048];} decision_t; 12 typedef union { unsigned short s[16384]; __m64 v[4096];} metric_t; 13 14 static union branchtab615 { unsigned short s[8192]; __m64 v[2048];} Branchtab615[6]; 15 static int Init = 0; 16 17 /* State info for instance of Viterbi decoder */ 18 struct v615 { 19 metric_t metrics1; /* path metric buffer 1 */ 20 metric_t metrics2; /* path metric buffer 2 */ 21 void *dp; /* Pointer to current decision */ 22 metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ 23 void *decisions; /* Beginning of decisions for block */ 24 }; 25 26 /* Initialize Viterbi decoder for start of new frame */ 27 int init_viterbi615_mmx(void *p,int starting_state){ 28 struct v615 *vp = p; 29 int i; 30 31 if(p == NULL) 32 return -1; 33 for(i=0;i<16384;i++) 34 vp->metrics1.s[i] = 5000; 35 36 vp->old_metrics = &vp->metrics1; 37 vp->new_metrics = &vp->metrics2; 38 vp->dp = vp->decisions; 39 vp->old_metrics->s[starting_state & 16383] = 0; /* Bias known start state */ 40 return 0; 41 } 42 43 /* Create a new instance of a Viterbi decoder */ 44 void *create_viterbi615_mmx(int len){ 45 struct v615 *vp; 46 47 if(!Init){ 48 int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF }; 49 set_viterbi615_polynomial_mmx(polys); 50 } 51 52 if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL) 53 return NULL; 54 if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){ 55 free(vp); 56 return NULL; 57 } 58 init_viterbi615_mmx(vp,0); 59 return vp; 60 } 61 62 void set_viterbi615_polynomial_mmx(int polys[6]){ 63 int state; 64 int i; 65 66 for(state=0;state < 8192;state++){ 67 for(i=0;i<6;i++) 68 Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0; 69 } 70 Init++; 71 } 72 73 /* Viterbi chainback */ 74 int chainback_viterbi615_mmx( 75 void *p, 76 unsigned char *data, /* Decoded output data */ 77 unsigned int nbits, /* Number of data bits */ 78 unsigned int endstate){ /* Terminal encoder state */ 79 struct v615 *vp = p; 80 decision_t *d; 81 82 if(p == NULL) 83 return -1; 84 85 d = (decision_t *)vp->decisions; 86 87 endstate %= 16384; 88 89 /* The store into data[] only needs to be done every 8 bits. 90 * But this avoids a conditional branch, and the writes will 91 * combine in the cache anyway 92 */ 93 d += 14; /* Look past tail */ 94 while(nbits-- != 0){ 95 int k; 96 97 k = d[nbits].c[endstate] & 1; 98 endstate = (k << 13) | (endstate >> 1); 99 data[nbits>>3] = endstate >> 6; 100 } 101 return 0; 102 } 103 104 /* Delete instance of a Viterbi decoder */ 105 void delete_viterbi615_mmx(void *p){ 106 struct v615 *vp = p; 107 108 if(vp != NULL){ 109 free(vp->decisions); 110 free(vp); 111 } 112 } 113 114 115 int update_viterbi615_blk_mmx(void *p,unsigned char *syms,int nbits){ 116 struct v615 *vp = p; 117 decision_t *d; 118 119 if(p == NULL) 120 return -1; 121 122 d = (decision_t *)vp->dp; 123 124 while(nbits--){ 125 __m64 sym0v,sym1v,sym2v,sym3v,sym4v,sym5v; 126 void *tmp; 127 int i; 128 129 /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */ 130 sym0v = _mm_set1_pi16(syms[0]); 131 sym1v = _mm_set1_pi16(syms[1]); 132 sym2v = _mm_set1_pi16(syms[2]); 133 sym3v = _mm_set1_pi16(syms[3]); 134 sym4v = _mm_set1_pi16(syms[4]); 135 sym5v = _mm_set1_pi16(syms[5]); 136 syms += 6; 137 138 for(i=0;i<2048;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 0-1530 145 */ 146 m0 = _mm_add_pi16(_mm_xor_si64(Branchtab615[0].v[i],sym0v),_mm_xor_si64(Branchtab615[1].v[i],sym1v)); 147 m1 = _mm_add_pi16(_mm_xor_si64(Branchtab615[2].v[i],sym2v),_mm_xor_si64(Branchtab615[3].v[i],sym3v)); 148 m2 = _mm_add_pi16(_mm_xor_si64(Branchtab615[4].v[i],sym4v),_mm_xor_si64(Branchtab615[5].v[i],sym5v)); 149 metric = _mm_add_pi16(m0,_mm_add_pi16(m1,m2)); 150 m_metric = _mm_sub_pi16(_mm_set1_pi16(1530),metric); 151 152 /* Add branch metrics to path metrics */ 153 m0 = _mm_add_pi16(vp->old_metrics->v[i],metric); 154 m3 = _mm_add_pi16(vp->old_metrics->v[2048+i],metric); 155 m1 = _mm_add_pi16(vp->old_metrics->v[2048+i],m_metric); 156 m2 = _mm_add_pi16(vp->old_metrics->v[i],m_metric); 157 158 /* Compare and select 159 * There's no packed min instruction in MMX, so we use modulo arithmetic 160 * to form the decisions and then do the select the hard way 161 */ 162 decision0 = _mm_cmpgt_pi16(_mm_sub_pi16(m0,m1),_mm_setzero_si64()); 163 decision1 = _mm_cmpgt_pi16(_mm_sub_pi16(m2,m3),_mm_setzero_si64()); 164 survivor0 = _mm_or_si64(_mm_and_si64(decision0,m1),_mm_andnot_si64(decision0,m0)); 165 survivor1 = _mm_or_si64(_mm_and_si64(decision1,m3),_mm_andnot_si64(decision1,m2)); 166 167 /* Merge decisions and store as bytes */ 168 d->v[i] = _mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64())); 169 170 /* Store surviving metrics */ 171 vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1); 172 vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1); 173 } 174 d++; 175 /* Swap pointers to old and new metrics */ 176 tmp = vp->old_metrics; 177 vp->old_metrics = vp->new_metrics; 178 vp->new_metrics = tmp; 179 } 180 vp->dp = d; 181 _mm_empty(); 182 return 0; 183 } 184
