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210 lines
6.7 KiB
210 lines
6.7 KiB
/* K=7 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec instructions |
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* Feb 2004, Phil Karn, KA9Q |
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*/ |
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#include <stdio.h> |
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#include <memory.h> |
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#include <stdlib.h> |
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#include "fec.h" |
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typedef union { long long p; unsigned char c[64]; vector bool char v[4]; } decision_t; |
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typedef union { long long p; unsigned char c[64]; vector unsigned char v[4]; } metric_t; |
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static union branchtab27 { unsigned char c[32]; vector unsigned char v[2];} Branchtab27[2]; |
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static int Init = 0; |
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/* State info for instance of Viterbi decoder |
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* Don't change this without also changing references in [mmx|sse|sse2]bfly29.s! |
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*/ |
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struct v27 { |
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metric_t metrics1; /* path metric buffer 1 */ |
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metric_t metrics2; /* path metric buffer 2 */ |
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decision_t *dp; /* Pointer to current decision */ |
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metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ |
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decision_t *decisions; /* Beginning of decisions for block */ |
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}; |
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/* Initialize Viterbi decoder for start of new frame */ |
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int init_viterbi27_av(void *p,int starting_state){ |
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struct v27 *vp = p; |
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int i; |
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if(p == NULL) |
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return -1; |
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for(i=0;i<4;i++) |
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vp->metrics1.v[i] = (vector unsigned char)(63); |
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vp->old_metrics = &vp->metrics1; |
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vp->new_metrics = &vp->metrics2; |
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vp->dp = vp->decisions; |
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vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */ |
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return 0; |
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} |
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void set_viterbi27_polynomial_av(int polys[2]){ |
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int state; |
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for(state=0;state < 32;state++){ |
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Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0; |
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Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0; |
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} |
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Init++; |
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} |
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/* Create a new instance of a Viterbi decoder */ |
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void *create_viterbi27_av(int len){ |
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struct v27 *vp; |
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if(!Init){ |
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int polys[2] = { V27POLYA,V27POLYB }; |
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set_viterbi27_polynomial_av(polys); |
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} |
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if((vp = (struct v27 *)malloc(sizeof(struct v27))) == NULL) |
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return NULL; |
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if((vp->decisions = (decision_t *)malloc((len+6)*sizeof(decision_t))) == NULL){ |
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free(vp); |
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return NULL; |
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} |
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init_viterbi27_av(vp,0); |
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return vp; |
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} |
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/* Viterbi chainback */ |
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int chainback_viterbi27_av( |
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void *p, |
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unsigned char *data, /* Decoded output data */ |
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unsigned int nbits, /* Number of data bits */ |
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unsigned int endstate){ /* Terminal encoder state */ |
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struct v27 *vp = p; |
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decision_t *d = (decision_t *)vp->decisions; |
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if(p == NULL) |
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return -1; |
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/* Make room beyond the end of the encoder register so we can |
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* accumulate a full byte of decoded data |
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*/ |
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endstate %= 64; |
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endstate <<= 2; |
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/* The store into data[] only needs to be done every 8 bits. |
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* But this avoids a conditional branch, and the writes will |
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* combine in the cache anyway |
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*/ |
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d += 6; /* Look past tail */ |
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while(nbits-- != 0){ |
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int k; |
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k = d[nbits].c[endstate>>2] & 1; |
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data[nbits>>3] = endstate = (endstate >> 1) | (k << 7); |
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} |
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return 0; |
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} |
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/* Delete instance of a Viterbi decoder */ |
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void delete_viterbi27_av(void *p){ |
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struct v27 *vp = p; |
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if(vp != NULL){ |
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free(vp->decisions); |
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free(vp); |
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} |
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} |
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/* Process received symbols */ |
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int update_viterbi27_blk_av(void *p,unsigned char *syms,int nbits){ |
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struct v27 *vp = p; |
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decision_t *d; |
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if(p == NULL) |
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return -1; |
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d = (decision_t *)vp->dp; |
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while(nbits--){ |
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vector unsigned char survivor0,survivor1,sym0v,sym1v; |
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vector bool char decision0,decision1; |
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vector unsigned char metric,m_metric,m0,m1,m2,m3; |
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void *tmp; |
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/* sym0v.0 = syms[0]; sym0v.1 = syms[1] */ |
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sym0v = vec_perm(vec_ld(0,syms),vec_ld(1,syms),vec_lvsl(0,syms)); |
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sym1v = vec_splat(sym0v,1); /* Splat syms[1] across sym1v */ |
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sym0v = vec_splat(sym0v,0); /* Splat syms[0] across sym0v */ |
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syms += 2; |
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/* Do the 32 butterflies as two interleaved groups of 16 each to keep the pipes full */ |
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/* Form first set of 16 branch metrics */ |
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metric = vec_avg(vec_xor(Branchtab27[0].v[0],sym0v),vec_xor(Branchtab27[1].v[0],sym1v)); |
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metric = vec_sr(metric,(vector unsigned char)(3)); |
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m_metric = vec_sub((vector unsigned char)(31),metric); |
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/* Form first set of path metrics */ |
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m0 = vec_adds(vp->old_metrics->v[0],metric); |
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m3 = vec_adds(vp->old_metrics->v[2],metric); |
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m1 = vec_adds(vp->old_metrics->v[2],m_metric); |
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m2 = vec_adds(vp->old_metrics->v[0],m_metric); |
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/* Form second set of 16 branch metrics */ |
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metric = vec_avg(vec_xor(Branchtab27[0].v[1],sym0v),vec_xor(Branchtab27[1].v[1],sym1v)); |
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metric = vec_sr(metric,(vector unsigned char)(3)); |
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m_metric = vec_sub((vector unsigned char)(31),metric); |
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/* Compare and select first set */ |
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decision0 = vec_cmpgt(m0,m1); |
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decision1 = vec_cmpgt(m2,m3); |
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survivor0 = vec_min(m0,m1); |
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survivor1 = vec_min(m2,m3); |
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/* Compute second set of path metrics */ |
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m0 = vec_adds(vp->old_metrics->v[1],metric); |
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m3 = vec_adds(vp->old_metrics->v[3],metric); |
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m1 = vec_adds(vp->old_metrics->v[3],m_metric); |
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m2 = vec_adds(vp->old_metrics->v[1],m_metric); |
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/* Interleave and store first decisions and survivors */ |
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d->v[0] = vec_mergeh(decision0,decision1); |
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d->v[1] = vec_mergel(decision0,decision1); |
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vp->new_metrics->v[0] = vec_mergeh(survivor0,survivor1); |
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vp->new_metrics->v[1] = vec_mergel(survivor0,survivor1); |
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/* Compare and select second set */ |
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decision0 = vec_cmpgt(m0,m1); |
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decision1 = vec_cmpgt(m2,m3); |
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survivor0 = vec_min(m0,m1); |
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survivor1 = vec_min(m2,m3); |
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/* Interleave and store second set of decisions and survivors */ |
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d->v[2] = vec_mergeh(decision0,decision1); |
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d->v[3] = vec_mergel(decision0,decision1); |
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vp->new_metrics->v[2] = vec_mergeh(survivor0,survivor1); |
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vp->new_metrics->v[3] = vec_mergel(survivor0,survivor1); |
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/* renormalize if necessary */ |
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if(vp->new_metrics->c[0] >= 105){ |
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vector unsigned char scale0,scale1; |
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/* Find smallest metric and splat */ |
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scale0 = vec_min(vp->new_metrics->v[0],vp->new_metrics->v[1]); |
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scale1 = vec_min(vp->new_metrics->v[2],vp->new_metrics->v[3]); |
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scale0 = vec_min(scale0,scale1); |
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,8)); |
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,4)); |
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,2)); |
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,1)); |
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/* Now subtract from all metrics */ |
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vp->new_metrics->v[0] = vec_subs(vp->new_metrics->v[0],scale0); |
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vp->new_metrics->v[1] = vec_subs(vp->new_metrics->v[1],scale0); |
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vp->new_metrics->v[2] = vec_subs(vp->new_metrics->v[2],scale0); |
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vp->new_metrics->v[3] = vec_subs(vp->new_metrics->v[3],scale0); |
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} |
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d++; |
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/* Swap pointers to old and new metrics */ |
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tmp = vp->old_metrics; |
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vp->old_metrics = vp->new_metrics; |
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vp->new_metrics = tmp; |
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} |
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vp->dp = d; |
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return 0; |
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} |
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