diff options
Diffstat (limited to 'viterbi39_mmx.c')
| -rw-r--r-- | viterbi39_mmx.c | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/viterbi39_mmx.c b/viterbi39_mmx.c new file mode 100644 index 0000000..875391a --- /dev/null +++ b/viterbi39_mmx.c @@ -0,0 +1,185 @@ +/* K=9 r=1/3 Viterbi decoder for x86 MMX + * Aug 2006, 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[256]; __m64 v[32];} decision_t; +typedef union { unsigned short s[256]; __m64 v[64];} metric_t; + +static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3]; +static int Init = 0; + +/* State info for instance of Viterbi decoder */ +struct v39 { + 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_viterbi39_mmx(void *p,int starting_state){ + struct v39 *vp = p; + int i; + + if(p == NULL) + return -1; + for(i=0;i<256;i++) + vp->metrics1.s[i] = 1000; + + vp->old_metrics = &vp->metrics1; + vp->new_metrics = &vp->metrics2; + vp->dp = vp->decisions; + vp->old_metrics->s[starting_state & 255] = 0; /* Bias known start state */ + return 0; +} + +void set_viterbi39_polynomial_mmx(int polys[3]){ + int state; + + for(state=0;state < 128;state++){ + Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0; + Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0; + Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0; + } + Init++; +} + +/* Create a new instance of a Viterbi decoder */ +void *create_viterbi39_mmx(int len){ + struct v39 *vp; + + if(!Init){ + int polys[3] = { V39POLYA,V39POLYB,V39POLYC }; + set_viterbi39_polynomial_mmx(polys); + } + if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL) + return NULL; + if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){ + free(vp); + return NULL; + } + init_viterbi39_mmx(vp,0); + return vp; +} + + + +/* Viterbi chainback */ +int chainback_viterbi39_mmx( + void *p, + unsigned char *data, /* Decoded output data */ + unsigned int nbits, /* Number of data bits */ + unsigned int endstate){ /* Terminal encoder state */ + struct v39 *vp = p; + decision_t *d; + int path_metric; + + if(p == NULL) + return -1; + + d = (decision_t *)vp->decisions; + + endstate %= 256; + + path_metric = vp->old_metrics->s[endstate]; + + /* 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 += 8; /* Look past tail */ + while(nbits-- != 0){ + int k; + + k = d[nbits].c[endstate] & 1; + endstate = (k << 7) | (endstate >> 1); + data[nbits>>3] = endstate; + } + return path_metric; +} + +/* Delete instance of a Viterbi decoder */ +void delete_viterbi39_mmx(void *p){ + struct v39 *vp = p; + + if(vp != NULL){ + free(vp->decisions); + free(vp); + } +} + + +int update_viterbi39_blk_mmx(void *p,unsigned char *syms,int nbits){ + struct v39 *vp = p; + decision_t *d; + int path_metric = 0; + + if(p == NULL) + return -1; + + d = (decision_t *)vp->dp; + + while(nbits--){ + __m64 sym0v,sym1v,sym2v; + 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]); + syms += 3; + + for(i=0;i<32;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(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v)); + metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0); + m_metric = _mm_sub_pi16(_mm_set1_pi16(765),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[32+i],metric); + m1 = _mm_add_pi16(vp->old_metrics->v[32+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); + } + if(vp->new_metrics->s[0] < vp->old_metrics->s[0]) + path_metric += 65536; /* Hack: wraparound probably occured */ + 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 path_metric; +} |