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/* K=7 r=1/2 Viterbi decoder for SSE2
* Feb 2004, Phil Karn, KA9Q
*/
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <xmmintrin.h>
#include "fec.h"
typedef union { unsigned char c[64]; __m128i v[4]; } metric_t;
typedef union { unsigned long w[2]; unsigned char c[8]; unsigned short s[4]; __m64 v[1];} decision_t;
union branchtab27 { unsigned char c[32]; __m128i v[2];} Branchtab27_sse2[2];
static int Init = 0;
/* State info for instance of Viterbi decoder
* Don't change this without also changing references in sse2bfly27.s!
*/
struct v27 {
metric_t metrics1; /* path metric buffer 1 */
metric_t metrics2; /* path metric buffer 2 */
decision_t *dp; /* Pointer to current decision */
metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
decision_t *decisions; /* Beginning of decisions for block */
};
/* Initialize Viterbi decoder for start of new frame */
int init_viterbi27_sse2(void *p,int starting_state){
struct v27 *vp = p;
int i;
if(p == NULL)
return -1;
for(i=0;i<64;i++)
vp->metrics1.c[i] = 63;
vp->old_metrics = &vp->metrics1;
vp->new_metrics = &vp->metrics2;
vp->dp = vp->decisions;
vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
return 0;
}
void set_viterbi27_polynomial_sse2(int polys[2]){
int state;
for(state=0;state < 32;state++){
Branchtab27_sse2[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
Branchtab27_sse2[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
}
Init++;
}
/* Create a new instance of a Viterbi decoder */
void *create_viterbi27_sse2(int len){
void *p;
struct v27 *vp;
if(!Init){
int polys[2] = { V27POLYA, V27POLYB };
set_viterbi27_polynomial_sse2(polys);
}
/* Ordinary malloc() only returns 8-byte alignment, we need 16 */
if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v27)))
return NULL;
vp = (struct v27 *)p;
if((p = malloc((len+6)*sizeof(decision_t))) == NULL){
free(vp);
return NULL;
}
vp->decisions = (decision_t *)p;
init_viterbi27_sse2(vp,0);
return vp;
}
/* Viterbi chainback */
int chainback_viterbi27_sse2(
void *p,
unsigned char *data, /* Decoded output data */
unsigned int nbits, /* Number of data bits */
unsigned int endstate){ /* Terminal encoder state */
struct v27 *vp = p;
decision_t *d;
if(p == NULL)
return -1;
d = vp->decisions;
/* Make room beyond the end of the encoder register so we can
* accumulate a full byte of decoded data
*/
endstate %= 64;
endstate <<= 2;
/* 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 += 6; /* Look past tail */
while(nbits-- != 0){
int k;
k = (d[nbits].c[(endstate>>2)/8] >> ((endstate>>2)%8)) & 1;
data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
}
return 0;
}
/* Delete instance of a Viterbi decoder */
void delete_viterbi27_sse2(void *p){
struct v27 *vp = p;
if(vp != NULL){
free(vp->decisions);
free(vp);
}
}
#if 0
/* This code is turned off because it's slower than my hand-crafted assembler in sse2bfly27.s. But it does work. */
void update_viterbi27_blk_sse2(void *p,unsigned char *syms,int nbits){
struct v27 *vp = p;
decision_t *d;
if(p == NULL)
return;
d = (decision_t *)vp->dp;
while(nbits--){
__m128i sym0v,sym1v;
void *tmp;
int i;
/* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
sym0v = _mm_set1_epi8(syms[0]);
sym1v = _mm_set1_epi8(syms[1]);
syms += 2;
for(i=0;i<2;i++){
__m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
/* Form branch metrics */
metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[i],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[i],sym1v));
/* There's no packed bytes right shift in SSE2, so we use the word version and mask
* (I'm *really* starting to like Altivec...)
*/
metric = _mm_srli_epi16(metric,3);
metric = _mm_and_si128(metric,_mm_set1_epi8(31));
m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric);
/* Add branch metrics to path metrics */
m0 = _mm_add_epi8(vp->old_metrics->v[i],metric);
m3 = _mm_add_epi8(vp->old_metrics->v[2+i],metric);
m1 = _mm_add_epi8(vp->old_metrics->v[2+i],m_metric);
m2 = _mm_add_epi8(vp->old_metrics->v[i],m_metric);
/* Compare and select, using modulo arithmetic */
decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128());
decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128());
survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0));
survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2));
/* Pack each set of decisions into 16 bits */
d->s[2*i] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1));
d->s[2*i+1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1));
/* Store surviving metrics */
vp->new_metrics->v[2*i] = _mm_unpacklo_epi8(survivor0,survivor1);
vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi8(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;
}
#endif
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