218 lines
6.0 KiB
C
218 lines
6.0 KiB
C
/* K=9 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec
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* Copyright Feb 2004, Phil Karn, KA9Q
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* May be used under the terms of the GNU Lesser General Public License (LGPL)
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <memory.h>
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#include <sys/sysctl.h>
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#include "fec.h"
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typedef union {
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unsigned char c[256];
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vector bool char v[16];
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} decision_t;
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typedef union {
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unsigned char c[256];
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vector unsigned char v[16];
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} metric_t;
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static union branchtab29 {
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unsigned char c[128];
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vector unsigned char v[8];
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} Branchtab29[2];
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static int Init = 0;
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/* State info for instance of Viterbi decoder */
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struct v29 {
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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_viterbi29_av(void *p, int starting_state)
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{
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struct v29 *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 < 16; 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 & 255] = 0; /* Bias known start state */
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return 0;
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}
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void set_viterbi29_polynomial_av(int polys[2])
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{
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int state;
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for (state = 0; state < 128; state++) {
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Branchtab29[0].c[state] = (polys[0] < 0) ^ parity((2 * state) & abs(
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polys[0])) ? 255 : 0;
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Branchtab29[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_viterbi29_av(int len)
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{
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struct v29 *vp;
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if (!Init) {
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int polys[2] = { V29POLYA, V29POLYB };
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set_viterbi29_polynomial_av(polys);
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}
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if ((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL) {
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return NULL;
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}
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if ((vp->decisions = (decision_t *)malloc((len + 8) * 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_viterbi29_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_viterbi29_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 v29 *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->decisions;
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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 %= 256;
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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 += 8; /* 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] & 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_viterbi29_av(void *p)
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{
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struct v29 *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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int update_viterbi29_blk_av(void *p, unsigned char *syms, int nbits)
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{
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struct v29 *vp = p;
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decision_t *d;
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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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d = (decision_t *)vp->dp;
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while (nbits--) {
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vector unsigned char sym1v, sym2v;
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void *tmp;
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/* All this seems necessary just to load a byte into all elements of a vector! */
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sym1v = vec_perm(vec_ld(0, syms), vec_ld(1, syms), vec_lvsl(0,
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syms)); /* sym1v.0 = syms[0]; sym1v.1 = syms[1] */
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sym2v = vec_splat(sym1v, 1); /* Splat syms[1] across sym2v */
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sym1v = vec_splat(sym1v, 0); /* Splat syms[0] across sym1v */
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syms += 2;
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for (i = 0; i < 8; i++) {
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vector bool char decision0, decision1;
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vector unsigned char metric, m_metric, m0, m1, m2, m3, survivor0, survivor1;
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/* Form branch metrics */
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metric = vec_avg(vec_xor(Branchtab29[0].v[i], sym1v),
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vec_xor(Branchtab29[1].v[i], sym2v));
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metric = vec_sr(metric, (vector unsigned char)(3));
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m_metric = (vector unsigned char)(31) - metric;
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/* Add branch metrics to path metrics */
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m0 = vec_adds(vp->old_metrics->v[i], metric);
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m3 = vec_adds(vp->old_metrics->v[8 + i], metric);
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m1 = vec_adds(vp->old_metrics->v[8 + i], m_metric);
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m2 = vec_adds(vp->old_metrics->v[i], m_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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/* Interleave and store decisions and survivors */
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d->v[2 * i] = vec_mergeh(decision0, decision1);
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d->v[2 * i + 1] = vec_mergel(decision0, decision1);
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vp->new_metrics->v[2 * i] = vec_mergeh(survivor0, survivor1);
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vp->new_metrics->v[2 * i + 1] = vec_mergel(survivor0, survivor1);
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}
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d++;
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/* renormalize if necessary */
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if (vp->new_metrics->c[0] >= 50) {
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int i;
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vector unsigned char scale0, scale1;
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/* Find smallest metric and splat */
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scale0 = vp->new_metrics->v[0];
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scale1 = vp->new_metrics->v[1];
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for (i = 2; i < 16; i += 2) {
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scale0 = vec_min(scale0, vp->new_metrics->v[i]);
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scale1 = vec_min(scale1, vp->new_metrics->v[i + 1]);
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}
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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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for (i = 0; i < 16; i++) {
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vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i], scale0);
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}
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}
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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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