| /* K=15 r=1/6 Viterbi decoder for x86 MMX |
| * Mar 2004, Phil Karn, KA9Q |
| * May be used under the terms of the GNU Lesser General Public License (LGPL) |
| */ |
| #include <mmintrin.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <memory.h> |
| #include "fec.h" |
| |
| typedef union { unsigned char c[16384]; __m64 v[2048];} decision_t; |
| typedef union { unsigned short s[16384]; __m64 v[4096];} metric_t; |
| |
| static union branchtab615 { unsigned short s[8192]; __m64 v[2048];} Branchtab615[6]; |
| static int Init = 0; |
| |
| /* State info for instance of Viterbi decoder */ |
| struct v615 { |
| metric_t metrics1; /* path metric buffer 1 */ |
| metric_t metrics2; /* path metric buffer 2 */ |
| void *dp; /* Pointer to current decision */ |
| metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ |
| void *decisions; /* Beginning of decisions for block */ |
| }; |
| |
| /* Initialize Viterbi decoder for start of new frame */ |
| int init_viterbi615_mmx(void *p,int starting_state){ |
| struct v615 *vp = p; |
| int i; |
| |
| if(p == NULL) |
| return -1; |
| for(i=0;i<16384;i++) |
| vp->metrics1.s[i] = 5000; |
| |
| vp->old_metrics = &vp->metrics1; |
| vp->new_metrics = &vp->metrics2; |
| vp->dp = vp->decisions; |
| vp->old_metrics->s[starting_state & 16383] = 0; /* Bias known start state */ |
| return 0; |
| } |
| |
| /* Create a new instance of a Viterbi decoder */ |
| void *create_viterbi615_mmx(int len){ |
| struct v615 *vp; |
| |
| if(!Init){ |
| int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF }; |
| set_viterbi615_polynomial_mmx(polys); |
| } |
| |
| if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL) |
| return NULL; |
| if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){ |
| free(vp); |
| return NULL; |
| } |
| init_viterbi615_mmx(vp,0); |
| return vp; |
| } |
| |
| void set_viterbi615_polynomial_mmx(int polys[6]){ |
| int state; |
| int i; |
| |
| for(state=0;state < 8192;state++){ |
| for(i=0;i<6;i++) |
| Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0; |
| } |
| Init++; |
| } |
| |
| /* Viterbi chainback */ |
| int chainback_viterbi615_mmx( |
| void *p, |
| unsigned char *data, /* Decoded output data */ |
| unsigned int nbits, /* Number of data bits */ |
| unsigned int endstate){ /* Terminal encoder state */ |
| struct v615 *vp = p; |
| decision_t *d; |
| |
| if(p == NULL) |
| return -1; |
| |
| d = (decision_t *)vp->decisions; |
| |
| endstate %= 16384; |
| |
| /* The store into data[] only needs to be done every 8 bits. |
| * But this avoids a conditional branch, and the writes will |
| * combine in the cache anyway |
| */ |
| d += 14; /* Look past tail */ |
| while(nbits-- != 0){ |
| int k; |
| |
| k = d[nbits].c[endstate] & 1; |
| endstate = (k << 13) | (endstate >> 1); |
| data[nbits>>3] = endstate >> 6; |
| } |
| return 0; |
| } |
| |
| /* Delete instance of a Viterbi decoder */ |
| void delete_viterbi615_mmx(void *p){ |
| struct v615 *vp = p; |
| |
| if(vp != NULL){ |
| free(vp->decisions); |
| free(vp); |
| } |
| } |
| |
| |
| int update_viterbi615_blk_mmx(void *p,unsigned char *syms,int nbits){ |
| struct v615 *vp = p; |
| decision_t *d; |
| |
| if(p == NULL) |
| return -1; |
| |
| d = (decision_t *)vp->dp; |
| |
| while(nbits--){ |
| __m64 sym0v,sym1v,sym2v,sym3v,sym4v,sym5v; |
| void *tmp; |
| int i; |
| |
| /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */ |
| sym0v = _mm_set1_pi16(syms[0]); |
| sym1v = _mm_set1_pi16(syms[1]); |
| sym2v = _mm_set1_pi16(syms[2]); |
| sym3v = _mm_set1_pi16(syms[3]); |
| sym4v = _mm_set1_pi16(syms[4]); |
| sym5v = _mm_set1_pi16(syms[5]); |
| syms += 6; |
| |
| for(i=0;i<2048;i++){ |
| __m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1; |
| |
| /* Form branch metrics |
| * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255, |
| * the XOR operations constitute conditional negation. |
| * metric and m_metric (-metric) are in the range 0-1530 |
| */ |
| m0 = _mm_add_pi16(_mm_xor_si64(Branchtab615[0].v[i],sym0v),_mm_xor_si64(Branchtab615[1].v[i],sym1v)); |
| m1 = _mm_add_pi16(_mm_xor_si64(Branchtab615[2].v[i],sym2v),_mm_xor_si64(Branchtab615[3].v[i],sym3v)); |
| m2 = _mm_add_pi16(_mm_xor_si64(Branchtab615[4].v[i],sym4v),_mm_xor_si64(Branchtab615[5].v[i],sym5v)); |
| metric = _mm_add_pi16(m0,_mm_add_pi16(m1,m2)); |
| m_metric = _mm_sub_pi16(_mm_set1_pi16(1530),metric); |
| |
| /* Add branch metrics to path metrics */ |
| m0 = _mm_add_pi16(vp->old_metrics->v[i],metric); |
| m3 = _mm_add_pi16(vp->old_metrics->v[2048+i],metric); |
| m1 = _mm_add_pi16(vp->old_metrics->v[2048+i],m_metric); |
| m2 = _mm_add_pi16(vp->old_metrics->v[i],m_metric); |
| |
| /* Compare and select |
| * There's no packed min instruction in MMX, so we use modulo arithmetic |
| * to form the decisions and then do the select the hard way |
| */ |
| decision0 = _mm_cmpgt_pi16(_mm_sub_pi16(m0,m1),_mm_setzero_si64()); |
| decision1 = _mm_cmpgt_pi16(_mm_sub_pi16(m2,m3),_mm_setzero_si64()); |
| survivor0 = _mm_or_si64(_mm_and_si64(decision0,m1),_mm_andnot_si64(decision0,m0)); |
| survivor1 = _mm_or_si64(_mm_and_si64(decision1,m3),_mm_andnot_si64(decision1,m2)); |
| |
| /* Merge decisions and store as bytes */ |
| d->v[i] = _mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64())); |
| |
| /* Store surviving metrics */ |
| vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1); |
| vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1); |
| } |
| d++; |
| /* Swap pointers to old and new metrics */ |
| tmp = vp->old_metrics; |
| vp->old_metrics = vp->new_metrics; |
| vp->new_metrics = tmp; |
| } |
| vp->dp = d; |
| _mm_empty(); |
| return 0; |
| } |