From 4e213d510f437769f8a28578dd4f786fb7d16c44 Mon Sep 17 00:00:00 2001 From: Bill Yi Date: Tue, 23 Jun 2015 13:53:11 -0700 Subject: Initial code --- viterbi615_sse2.c | 204 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 204 insertions(+) create mode 100644 viterbi615_sse2.c (limited to 'viterbi615_sse2.c') diff --git a/viterbi615_sse2.c b/viterbi615_sse2.c new file mode 100644 index 0000000..7f711e5 --- /dev/null +++ b/viterbi615_sse2.c @@ -0,0 +1,204 @@ +/* K=15 r=1/6 Viterbi decoder for x86 SSE2 + * Copyright Mar 2004, Phil Karn, KA9Q + * May be used under the terms of the GNU Lesser General Public License (LGPL) + */ +#include +#include +#include +#include +#include +#include "fec.h" + +typedef union { unsigned long w[512]; unsigned short s[1024];} decision_t; +typedef union { signed short s[16384]; __m128i v[2048];} metric_t; + +static union branchtab615 { unsigned short s[8192]; __m128i v[1024];} 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_sse2(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] = (SHRT_MIN+5000); + + vp->old_metrics = &vp->metrics1; + vp->new_metrics = &vp->metrics2; + vp->dp = vp->decisions; + vp->old_metrics->s[starting_state & 16383] = SHRT_MIN; /* Bias known start state */ + return 0; +} + +/* Create a new instance of a Viterbi decoder */ +void *create_viterbi615_sse2(int len){ + void *p; + struct v615 *vp; + + if(!Init){ + int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF }; + set_viterbi615_polynomial_sse2(polys); + } + + /* Ordinary malloc() only returns 8-byte alignment, we need 16 */ + if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v615))) + return NULL; + + vp = (struct v615 *)p; + if((p = malloc((len+14)*sizeof(decision_t))) == NULL){ + free(vp); + return NULL; + } + vp->decisions = (decision_t *)p; + init_viterbi615_sse2(vp,0); + return vp; +} + +void set_viterbi615_polynomial_sse2(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_sse2( + 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 = (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].w[endstate/32] >> (endstate%32)) & 1; + endstate = (k << 13) | (endstate >> 1); + data[nbits>>3] = endstate >> 6; + } + return 0; +} + +/* Delete instance of a Viterbi decoder */ +void delete_viterbi615_sse2(void *p){ + struct v615 *vp = p; + + if(vp != NULL){ + free(vp->decisions); + free(vp); + } +} + + +int update_viterbi615_blk_sse2(void *p,unsigned char *syms,int nbits){ + struct v615 *vp = p; + decision_t *d = (decision_t *)vp->dp; + + while(nbits--){ + __m128i 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_epi16(syms[0]); + sym1v = _mm_set1_epi16(syms[1]); + sym2v = _mm_set1_epi16(syms[2]); + sym3v = _mm_set1_epi16(syms[3]); + sym4v = _mm_set1_epi16(syms[4]); + sym5v = _mm_set1_epi16(syms[5]); + syms += 6; + + /* SSE2 doesn't support saturated adds on unsigned shorts, so we have to use signed shorts */ + for(i=0;i<1024;i++){ + __m128i 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_epi16(_mm_xor_si128(Branchtab615[0].v[i],sym0v),_mm_xor_si128(Branchtab615[1].v[i],sym1v)); + m1 = _mm_add_epi16(_mm_xor_si128(Branchtab615[2].v[i],sym2v),_mm_xor_si128(Branchtab615[3].v[i],sym3v)); + m2 = _mm_add_epi16(_mm_xor_si128(Branchtab615[4].v[i],sym4v),_mm_xor_si128(Branchtab615[5].v[i],sym5v)); + metric = _mm_add_epi16(m0,_mm_add_epi16(m1,m2)); + m_metric = _mm_sub_epi16(_mm_set1_epi16(1530),metric); + + /* Add branch metrics to path metrics */ + m0 = _mm_adds_epi16(vp->old_metrics->v[i],metric); + m3 = _mm_adds_epi16(vp->old_metrics->v[1024+i],metric); + m1 = _mm_adds_epi16(vp->old_metrics->v[1024+i],m_metric); + m2 = _mm_adds_epi16(vp->old_metrics->v[i],m_metric); + + /* Compare and select */ + survivor0 = _mm_min_epi16(m0,m1); + survivor1 = _mm_min_epi16(m2,m3); + decision0 = _mm_cmpeq_epi16(survivor0,m1); + decision1 = _mm_cmpeq_epi16(survivor1,m3); + + /* Pack each set of decisions into 8 8-bit bytes, then interleave them and compress into 16 bits */ + d->s[i] = _mm_movemask_epi8(_mm_unpacklo_epi8(_mm_packs_epi16(decision0,_mm_setzero_si128()),_mm_packs_epi16(decision1,_mm_setzero_si128()))); + + /* Store surviving metrics */ + vp->new_metrics->v[2*i] = _mm_unpacklo_epi16(survivor0,survivor1); + vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi16(survivor0,survivor1); + } + /* See if we need to renormalize + * Max metric spread for this code with 0-90 branch metrics is 405 + */ + if(vp->new_metrics->s[0] >= SHRT_MAX-12750){ + int i,adjust; + __m128i adjustv; + union { __m128i v; signed short w[8]; } t; + + /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */ + adjustv = vp->new_metrics->v[0]; + for(i=1;i<2048;i++) + adjustv = _mm_min_epi16(adjustv,vp->new_metrics->v[i]); + + adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,8)); + adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,4)); + adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,2)); + t.v = adjustv; + adjust = t.w[0] - SHRT_MIN; + adjustv = _mm_set1_epi16(adjust); + + /* We cannot use a saturated subtract, because we often have to adjust by more than SHRT_MAX + * This is okay since it can't overflow anyway + */ + for(i=0;i<2048;i++) + vp->new_metrics->v[i] = _mm_sub_epi16(vp->new_metrics->v[i],adjustv); + } + 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; + return 0; +} + + -- cgit v1.2.3