Bill Yi | 4e213d5 | 2015-06-23 13:53:11 -0700 | [diff] [blame] | 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 |