1 /* K=7 r=1/2 Viterbi decoder for SSE2 2 * Feb 2004, Phil Karn, KA9Q 3 */ 4 #include <stdio.h> 5 #include <stdlib.h> 6 #include <memory.h> 7 #include <xmmintrin.h> 8 #include "fec.h" 9 10 typedef union { unsigned char c[64]; __m128i v[4]; } metric_t; 11 typedef union { unsigned long w[2]; unsigned char c[8]; unsigned short s[4]; __m64 v[1];} decision_t; 12 union branchtab27 { unsigned char c[32]; __m128i v[2];} Branchtab27_sse2[2]; 13 static int Init = 0; 14 15 /* State info for instance of Viterbi decoder 16 * Don't change this without also changing references in sse2bfly27.s! 17 */ 18 struct v27 { 19 metric_t metrics1; /* path metric buffer 1 */ 20 metric_t metrics2; /* path metric buffer 2 */ 21 decision_t *dp; /* Pointer to current decision */ 22 metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ 23 decision_t *decisions; /* Beginning of decisions for block */ 24 }; 25 26 /* Initialize Viterbi decoder for start of new frame */ 27 int init_viterbi27_sse2(void *p,int starting_state){ 28 struct v27 *vp = p; 29 int i; 30 31 if(p == NULL) 32 return -1; 33 for(i=0;i<64;i++) 34 vp->metrics1.c[i] = 63; 35 36 vp->old_metrics = &vp->metrics1; 37 vp->new_metrics = &vp->metrics2; 38 vp->dp = vp->decisions; 39 vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */ 40 return 0; 41 } 42 43 void set_viterbi27_polynomial_sse2(int polys[2]){ 44 int state; 45 46 for(state=0;state < 32;state++){ 47 Branchtab27_sse2[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0; 48 Branchtab27_sse2[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0; 49 } 50 Init++; 51 } 52 53 54 /* Create a new instance of a Viterbi decoder */ 55 void *create_viterbi27_sse2(int len){ 56 void *p; 57 struct v27 *vp; 58 59 if(!Init){ 60 int polys[2] = { V27POLYA, V27POLYB }; 61 set_viterbi27_polynomial_sse2(polys); 62 } 63 /* Ordinary malloc() only returns 8-byte alignment, we need 16 */ 64 if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v27))) 65 return NULL; 66 vp = (struct v27 *)p; 67 68 if((p = malloc((len+6)*sizeof(decision_t))) == NULL){ 69 free(vp); 70 return NULL; 71 } 72 vp->decisions = (decision_t *)p; 73 init_viterbi27_sse2(vp,0); 74 75 return vp; 76 } 77 78 /* Viterbi chainback */ 79 int chainback_viterbi27_sse2( 80 void *p, 81 unsigned char *data, /* Decoded output data */ 82 unsigned int nbits, /* Number of data bits */ 83 unsigned int endstate){ /* Terminal encoder state */ 84 struct v27 *vp = p; 85 decision_t *d; 86 87 if(p == NULL) 88 return -1; 89 d = vp->decisions; 90 /* Make room beyond the end of the encoder register so we can 91 * accumulate a full byte of decoded data 92 */ 93 endstate %= 64; 94 endstate <<= 2; 95 96 /* The store into data[] only needs to be done every 8 bits. 97 * But this avoids a conditional branch, and the writes will 98 * combine in the cache anyway 99 */ 100 d += 6; /* Look past tail */ 101 while(nbits-- != 0){ 102 int k; 103 104 k = (d[nbits].c[(endstate>>2)/8] >> ((endstate>>2)%8)) & 1; 105 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7); 106 } 107 return 0; 108 } 109 110 /* Delete instance of a Viterbi decoder */ 111 void delete_viterbi27_sse2(void *p){ 112 struct v27 *vp = p; 113 114 if(vp != NULL){ 115 free(vp->decisions); 116 free(vp); 117 } 118 } 119 120 121 #if 0 122 /* This code is turned off because it's slower than my hand-crafted assembler in sse2bfly27.s. But it does work. */ 123 void update_viterbi27_blk_sse2(void *p,unsigned char *syms,int nbits){ 124 struct v27 *vp = p; 125 decision_t *d; 126 127 if(p == NULL) 128 return; 129 d = (decision_t *)vp->dp; 130 while(nbits--){ 131 __m128i sym0v,sym1v; 132 void *tmp; 133 int i; 134 135 /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */ 136 sym0v = _mm_set1_epi8(syms[0]); 137 sym1v = _mm_set1_epi8(syms[1]); 138 syms += 2; 139 140 for(i=0;i<2;i++){ 141 __m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1; 142 143 /* Form branch metrics */ 144 metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[i],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[i],sym1v)); 145 /* There's no packed bytes right shift in SSE2, so we use the word version and mask 146 * (I'm *really* starting to like Altivec...) 147 */ 148 metric = _mm_srli_epi16(metric,3); 149 metric = _mm_and_si128(metric,_mm_set1_epi8(31)); 150 m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric); 151 152 /* Add branch metrics to path metrics */ 153 m0 = _mm_add_epi8(vp->old_metrics->v[i],metric); 154 m3 = _mm_add_epi8(vp->old_metrics->v[2+i],metric); 155 m1 = _mm_add_epi8(vp->old_metrics->v[2+i],m_metric); 156 m2 = _mm_add_epi8(vp->old_metrics->v[i],m_metric); 157 158 /* Compare and select, using modulo arithmetic */ 159 decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128()); 160 decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128()); 161 survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0)); 162 survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2)); 163 164 /* Pack each set of decisions into 16 bits */ 165 d->s[2*i] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1)); 166 d->s[2*i+1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1)); 167 168 /* Store surviving metrics */ 169 vp->new_metrics->v[2*i] = _mm_unpacklo_epi8(survivor0,survivor1); 170 vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi8(survivor0,survivor1); 171 } 172 d++; 173 /* Swap pointers to old and new metrics */ 174 tmp = vp->old_metrics; 175 vp->old_metrics = vp->new_metrics; 176 vp->new_metrics = tmp; 177 } 178 vp->dp = d; 179 } 180 #endif 181
