239 lines
7.0 KiB
C
239 lines
7.0 KiB
C
/* 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 {
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long long p;
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unsigned char c[64];
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vector bool char v[4];
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} decision_t;
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typedef union {
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long long p;
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unsigned char c[64];
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vector unsigned char v[4];
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} metric_t;
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static union branchtab27 {
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unsigned char c[32];
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vector unsigned char v[2];
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} 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,
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*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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{
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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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}
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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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}
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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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{
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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(
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polys[0])) ? 255 : 0;
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Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2 * state) & abs(
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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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{
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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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}
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if ((vp->decisions = (decision_t *)malloc((len + 6) * sizeof(
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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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{
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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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}
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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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{
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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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{
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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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}
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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),
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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),
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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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