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Diffstat (limited to 'libtransport/src/protocols/fec/fec.cc')
| -rw-r--r-- | libtransport/src/protocols/fec/fec.cc | 838 |
1 files changed, 838 insertions, 0 deletions
diff --git a/libtransport/src/protocols/fec/fec.cc b/libtransport/src/protocols/fec/fec.cc new file mode 100644 index 000000000..16a04cb98 --- /dev/null +++ b/libtransport/src/protocols/fec/fec.cc @@ -0,0 +1,838 @@ +/* + * fec.c -- forward error correction based on Vandermonde matrices + * 980624 + * (C) 1997-98 Luigi Rizzo (luigi@iet.unipi.it) + * + * Portions derived from code by Phil Karn (karn@ka9q.ampr.org), + * Robert Morelos-Zaragoza (robert@spectra.eng.hawaii.edu) and Hari + * Thirumoorthy (harit@spectra.eng.hawaii.edu), Aug 1995 + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above + * copyright notice, this list of conditions and the following + * disclaimer in the documentation and/or other materials + * provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS + * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, + * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, + * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR + * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY + * OF SUCH DAMAGE. + */ + +/* + * The following parameter defines how many bits are used for + * field elements. The code supports any value from 2 to 16 + * but fastest operation is achieved with 8 bit elements + * This is the only parameter you may want to change. + */ +#ifndef GF_BITS +#define GF_BITS 8 /* code over GF(2**GF_BITS) - change to suit */ +#endif + +#include "fec.h" + +#include <hicn/transport/portability/platform.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +/** + * XXX This disable a warning raising only in some platforms. + * TODO Check if this warning is a mistake or it is a real bug: + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83404 + * https://gcc.gnu.org/bugzilla//show_bug.cgi?id=88059 + */ +#ifndef __clang__ +#pragma GCC diagnostic ignored "-Wstringop-overflow" +#endif + +/* + * compatibility stuff + */ +#ifdef MSDOS /* but also for others, e.g. sun... */ +#define NEED_BCOPY +#define bcmp(a, b, n) memcmp(a, b, n) +#endif + +#ifdef ANDROID +#define bcmp(a, b, n) memcmp(a, b, n) +#endif + +#ifdef NEED_BCOPY +#define bcopy(s, d, siz) memcpy((d), (s), (siz)) +#define bzero(d, siz) memset((d), '\0', (siz)) +#endif + +/* + * stuff used for testing purposes only + */ + +#ifdef TEST +#define DEB(x) +#define DDB(x) x +#define DEBUG 0 /* minimal debugging */ +#ifdef MSDOS +#include <time.h> +struct timeval { + unsigned long ticks; +}; +#define gettimeofday(x, dummy) \ + { (x)->ticks = clock(); } +#define DIFF_T(a, b) (1 + 1000000 * (a.ticks - b.ticks) / CLOCKS_PER_SEC) +typedef unsigned long u_long; +typedef unsigned short u_short; +#else /* typically, unix systems */ +#include <sys/time.h> +#define DIFF_T(a, b) \ + (1 + 1000000 * (a.tv_sec - b.tv_sec) + (a.tv_usec - b.tv_usec)) +#endif + +#define TICK(t) \ + { \ + struct timeval x; \ + gettimeofday(&x, NULL); \ + t = x.tv_usec + 1000000 * (x.tv_sec & 0xff); \ + } +#define TOCK(t) \ + { \ + u_long t1; \ + TICK(t1); \ + if (t1 < t) \ + t = 256000000 + t1 - t; \ + else \ + t = t1 - t; \ + if (t == 0) t = 1; \ + } + +u_long ticks[10]; /* vars for timekeeping */ +#else +#define DEB(x) +#define DDB(x) +#define TICK(x) +#define TOCK(x) +#endif /* TEST */ + +/* + * You should not need to change anything beyond this point. + * The first part of the file implements linear algebra in GF. + * + * gf is the type used to store an element of the Galois Field. + * Must constain at least GF_BITS bits. + * + * Note: unsigned char will work up to GF(256) but int seems to run + * faster on the Pentium. We use int whenever have to deal with an + * index, since they are generally faster. + */ +#if (GF_BITS < 2 && GF_BITS > 16) +#error "GF_BITS must be 2 .. 16" +#endif + +#define GF_SIZE ((1 << GF_BITS) - 1) /* powers of \alpha */ + +/* + * Primitive polynomials - see Lin & Costello, Appendix A, + * and Lee & Messerschmitt, p. 453. + */ +static const char *allPp[] = { + /* GF_BITS polynomial */ + NULL, /* 0 no code */ + NULL, /* 1 no code */ + "111", /* 2 1+x+x^2 */ + "1101", /* 3 1+x+x^3 */ + "11001", /* 4 1+x+x^4 */ + "101001", /* 5 1+x^2+x^5 */ + "1100001", /* 6 1+x+x^6 */ + "10010001", /* 7 1 + x^3 + x^7 */ + "101110001", /* 8 1+x^2+x^3+x^4+x^8 */ + "1000100001", /* 9 1+x^4+x^9 */ + "10010000001", /* 10 1+x^3+x^10 */ + "101000000001", /* 11 1+x^2+x^11 */ + "1100101000001", /* 12 1+x+x^4+x^6+x^12 */ + "11011000000001", /* 13 1+x+x^3+x^4+x^13 */ + "110000100010001", /* 14 1+x+x^6+x^10+x^14 */ + "1100000000000001", /* 15 1+x+x^15 */ + "11010000000010001" /* 16 1+x+x^3+x^12+x^16 */ +}; + +/* + * To speed up computations, we have tables for logarithm, exponent + * and inverse of a number. If GF_BITS <= 8, we use a table for + * multiplication as well (it takes 64K, no big deal even on a PDA, + * especially because it can be pre-initialized an put into a ROM!), + * otherwhise we use a table of logarithms. + * In any case the macro gf_mul(x,y) takes care of multiplications. + */ + +static gf gf_exp[2 * GF_SIZE]; /* index->poly form conversion table */ +static int gf_log[GF_SIZE + 1]; /* Poly->index form conversion table */ +static gf inverse[GF_SIZE + 1]; /* inverse of field elem. */ + /* inv[\alpha**i]=\alpha**(GF_SIZE-i-1) */ + +/* + * modnn(x) computes x % GF_SIZE, where GF_SIZE is 2**GF_BITS - 1, + * without a slow divide. + */ +static inline gf modnn(int x) { + while (x >= GF_SIZE) { + x -= GF_SIZE; + x = (x >> GF_BITS) + (x & GF_SIZE); + } + return x; +} + +#define SWAP(a, b, t) \ + { \ + t tmp; \ + tmp = a; \ + a = b; \ + b = tmp; \ + } + +/* + * gf_mul(x,y) multiplies two numbers. If GF_BITS<=8, it is much + * faster to use a multiplication table. + * + * USE_GF_MULC, GF_MULC0(c) and GF_ADDMULC(x) can be used when multiplying + * many numbers by the same constant. In this case the first + * call sets the constant, and others perform the multiplications. + * A value related to the multiplication is held in a local variable + * declared with USE_GF_MULC . See usage in addmul1(). + */ +#if (GF_BITS <= 8) +static gf gf_mul_table[GF_SIZE + 1][GF_SIZE + 1]; + +#define gf_mul(x, y) gf_mul_table[x][y] + +#define USE_GF_MULC gf *__gf_mulc_ +#define GF_MULC0(c) __gf_mulc_ = gf_mul_table[c] +#define GF_ADDMULC(dst, x) dst ^= __gf_mulc_[x] + +static void init_mul_table() { + int i, j; + for (i = 0; i < GF_SIZE + 1; i++) + for (j = 0; j < GF_SIZE + 1; j++) + gf_mul_table[i][j] = gf_exp[modnn(gf_log[i] + gf_log[j])]; + + for (j = 0; j < GF_SIZE + 1; j++) gf_mul_table[0][j] = gf_mul_table[j][0] = 0; +} +#else /* GF_BITS > 8 */ +static inline gf gf_mul(x, y) { + if ((x) == 0 || (y) == 0) return 0; + + return gf_exp[gf_log[x] + gf_log[y]]; +} +#define init_mul_table() + +#define USE_GF_MULC register gf *__gf_mulc_ +#define GF_MULC0(c) __gf_mulc_ = &gf_exp[gf_log[c]] +#define GF_ADDMULC(dst, x) \ + { \ + if (x) dst ^= __gf_mulc_[gf_log[x]]; \ + } +#endif + +/* + * Generate GF(2**m) from the irreducible polynomial p(X) in p[0]..p[m] + * Lookup tables: + * index->polynomial form gf_exp[] contains j= \alpha^i; + * polynomial form -> index form gf_log[ j = \alpha^i ] = i + * \alpha=x is the primitive element of GF(2^m) + * + * For efficiency, gf_exp[] has size 2*GF_SIZE, so that a simple + * multiplication of two numbers can be resolved without calling modnn + */ + +/* + * i use malloc so many times, it is easier to put checks all in + * one place. + */ +static void *my_malloc(int sz, const char *err_string) { + void *p = malloc(sz); + if (p == NULL) { + fprintf(stderr, "-- malloc failure allocating %s\n", err_string); + exit(1); + } + return p; +} + +#define NEW_GF_MATRIX(rows, cols) \ + (gf *)my_malloc(rows *cols * sizeof(gf), " ## __LINE__ ## ") + +/* + * initialize the data structures used for computations in GF. + */ +static void generate_gf(void) { + int i; + gf mask; + const char *Pp = allPp[GF_BITS]; + + mask = 1; /* x ** 0 = 1 */ + gf_exp[GF_BITS] = 0; /* will be updated at the end of the 1st loop */ + /* + * first, generate the (polynomial representation of) powers of \alpha, + * which are stored in gf_exp[i] = \alpha ** i . + * At the same time build gf_log[gf_exp[i]] = i . + * The first GF_BITS powers are simply bits shifted to the left. + */ + for (i = 0; i < GF_BITS; i++, mask <<= 1) { + gf_exp[i] = mask; + gf_log[gf_exp[i]] = i; + /* + * If Pp[i] == 1 then \alpha ** i occurs in poly-repr + * gf_exp[GF_BITS] = \alpha ** GF_BITS + */ + if (Pp[i] == '1') gf_exp[GF_BITS] ^= mask; + } + /* + * now gf_exp[GF_BITS] = \alpha ** GF_BITS is complete, so can als + * compute its inverse. + */ + gf_log[gf_exp[GF_BITS]] = GF_BITS; + /* + * Poly-repr of \alpha ** (i+1) is given by poly-repr of + * \alpha ** i shifted left one-bit and accounting for any + * \alpha ** GF_BITS term that may occur when poly-repr of + * \alpha ** i is shifted. + */ + mask = 1 << (GF_BITS - 1); + for (i = GF_BITS + 1; i < GF_SIZE; i++) { + if (gf_exp[i - 1] >= mask) + gf_exp[i] = gf_exp[GF_BITS] ^ ((gf_exp[i - 1] ^ mask) << 1); + else + gf_exp[i] = gf_exp[i - 1] << 1; + gf_log[gf_exp[i]] = i; + } + /* + * log(0) is not defined, so use a special value + */ + gf_log[0] = GF_SIZE; + /* set the extended gf_exp values for fast multiply */ + for (i = 0; i < GF_SIZE; i++) gf_exp[i + GF_SIZE] = gf_exp[i]; + + /* + * again special cases. 0 has no inverse. This used to + * be initialized to GF_SIZE, but it should make no difference + * since noone is supposed to read from here. + */ + inverse[0] = 0; + inverse[1] = 1; + for (i = 2; i <= GF_SIZE; i++) inverse[i] = gf_exp[GF_SIZE - gf_log[i]]; +} + +/* + * Various linear algebra operations that i use often. + */ + +/* + * addmul() computes dst[] = dst[] + c * src[] + * This is used often, so better optimize it! Currently the loop is + * unrolled 16 times, a good value for 486 and pentium-class machines. + * The case c=0 is also optimized, whereas c=1 is not. These + * calls are unfrequent in my typical apps so I did not bother. + * + * Note that gcc on + */ +#define addmul(dst, src, c, sz) \ + if (c != 0) addmul1(dst, src, c, sz) + +#define UNROLL 16 /* 1, 4, 8, 16 */ +static void addmul1(gf *dst1, gf *src1, gf c, int sz) { + USE_GF_MULC; + gf *dst = dst1, *src = src1; + gf *lim = &dst[sz - UNROLL + 1]; + + GF_MULC0(c); + +#if (UNROLL > 1) /* unrolling by 8/16 is quite effective on the pentium */ + for (; dst < lim; dst += UNROLL, src += UNROLL) { + GF_ADDMULC(dst[0], src[0]); + GF_ADDMULC(dst[1], src[1]); + GF_ADDMULC(dst[2], src[2]); + GF_ADDMULC(dst[3], src[3]); +#if (UNROLL > 4) + GF_ADDMULC(dst[4], src[4]); + GF_ADDMULC(dst[5], src[5]); + GF_ADDMULC(dst[6], src[6]); + GF_ADDMULC(dst[7], src[7]); +#endif +#if (UNROLL > 8) + GF_ADDMULC(dst[8], src[8]); + GF_ADDMULC(dst[9], src[9]); + GF_ADDMULC(dst[10], src[10]); + GF_ADDMULC(dst[11], src[11]); + GF_ADDMULC(dst[12], src[12]); + GF_ADDMULC(dst[13], src[13]); + GF_ADDMULC(dst[14], src[14]); + GF_ADDMULC(dst[15], src[15]); +#endif + } +#endif + lim += UNROLL - 1; + for (; dst < lim; dst++, src++) /* final components */ + GF_ADDMULC(*dst, *src); +} + +/* + * computes C = AB where A is n*k, B is k*m, C is n*m + */ +static void matmul(gf *a, gf *b, gf *c, int n, int k, int m) { + int row, col, i; + + for (row = 0; row < n; row++) { + for (col = 0; col < m; col++) { + gf *pa = &a[row * k]; + gf *pb = &b[col]; + gf acc = 0; + for (i = 0; i < k; i++, pa++, pb += m) acc ^= gf_mul(*pa, *pb); + c[row * m + col] = acc; + } + } +} + +#ifdef DEBUGG +/* + * returns 1 if the square matrix is identiy + * (only for test) + */ +static int is_identity(gf *m, int k) { + int row, col; + for (row = 0; row < k; row++) + for (col = 0; col < k; col++) + if ((row == col && *m != 1) || (row != col && *m != 0)) + return 0; + else + m++; + return 1; +} +#endif /* debug */ + +/* + * invert_mat() takes a matrix and produces its inverse + * k is the size of the matrix. + * (Gauss-Jordan, adapted from Numerical Recipes in C) + * Return non-zero if singular. + */ +DEB(int pivloops = 0; int pivswaps = 0; /* diagnostic */) +static int invert_mat(gf *src, int k) { + gf c, *p; + int irow, icol, row, col, i, ix; + + int error = 1; + int *indxc = (int *)my_malloc(k * sizeof(int), "indxc"); + int *indxr = (int *)my_malloc(k * sizeof(int), "indxr"); + int *ipiv = (int *)my_malloc(k * sizeof(int), "ipiv"); + gf *id_row = NEW_GF_MATRIX(1, k); + gf *temp_row = NEW_GF_MATRIX(1, k); + + bzero(id_row, k * sizeof(gf)); + DEB(pivloops = 0; pivswaps = 0; /* diagnostic */) + /* + * ipiv marks elements already used as pivots. + */ + for (i = 0; i < k; i++) ipiv[i] = 0; + + for (col = 0; col < k; col++) { + gf *pivot_row; + /* + * Zeroing column 'col', look for a non-zero element. + * First try on the diagonal, if it fails, look elsewhere. + */ + irow = icol = -1; + if (ipiv[col] != 1 && src[col * k + col] != 0) { + irow = col; + icol = col; + goto found_piv; + } + for (row = 0; row < k; row++) { + if (ipiv[row] != 1) { + for (ix = 0; ix < k; ix++) { + DEB(pivloops++;) + if (ipiv[ix] == 0) { + if (src[row * k + ix] != 0) { + irow = row; + icol = ix; + goto found_piv; + } + } else if (ipiv[ix] > 1) { + fprintf(stderr, "singular matrix\n"); + goto fail; + } + } + } + } + if (icol == -1) { + fprintf(stderr, "XXX pivot not found!\n"); + goto fail; + } + found_piv: + ++(ipiv[icol]); + /* + * swap rows irow and icol, so afterwards the diagonal + * element will be correct. Rarely done, not worth + * optimizing. + */ + if (irow != icol) { + for (ix = 0; ix < k; ix++) { + SWAP(src[irow * k + ix], src[icol * k + ix], gf); + } + } + indxr[col] = irow; + indxc[col] = icol; + pivot_row = &src[icol * k]; + c = pivot_row[icol]; + if (c == 0) { + fprintf(stderr, "singular matrix 2\n"); + goto fail; + } + if (c != 1) { /* otherwhise this is a NOP */ + /* + * this is done often , but optimizing is not so + * fruitful, at least in the obvious ways (unrolling) + */ + DEB(pivswaps++;) + c = inverse[c]; + pivot_row[icol] = 1; + for (ix = 0; ix < k; ix++) pivot_row[ix] = gf_mul(c, pivot_row[ix]); + } + /* + * from all rows, remove multiples of the selected row + * to zero the relevant entry (in fact, the entry is not zero + * because we know it must be zero). + * (Here, if we know that the pivot_row is the identity, + * we can optimize the addmul). + */ + id_row[icol] = 1; + if (bcmp(pivot_row, id_row, k * sizeof(gf)) != 0) { + for (p = src, ix = 0; ix < k; ix++, p += k) { + if (ix != icol) { + c = p[icol]; + p[icol] = 0; + addmul(p, pivot_row, c, k); + } + } + } + id_row[icol] = 0; + } /* done all columns */ + for (col = k - 1; col >= 0; col--) { + if (indxr[col] < 0 || indxr[col] >= k) + fprintf(stderr, "AARGH, indxr[col] %d\n", indxr[col]); + else if (indxc[col] < 0 || indxc[col] >= k) + fprintf(stderr, "AARGH, indxc[col] %d\n", indxc[col]); + else if (indxr[col] != indxc[col]) { + for (row = 0; row < k; row++) { + SWAP(src[row * k + indxr[col]], src[row * k + indxc[col]], gf); + } + } + } + error = 0; +fail: + free(indxc); + free(indxr); + free(ipiv); + free(id_row); + free(temp_row); + return error; +} + +/* + * fast code for inverting a vandermonde matrix. + * XXX NOTE: It assumes that the matrix + * is not singular and _IS_ a vandermonde matrix. Only uses + * the second column of the matrix, containing the p_i's. + * + * Algorithm borrowed from "Numerical recipes in C" -- sec.2.8, but + * largely revised for my purposes. + * p = coefficients of the matrix (p_i) + * q = values of the polynomial (known) + */ + +int invert_vdm(gf *src, int k) { + int i, j, row, col; + gf *b, *c, *p; + gf t, xx; + + if (k == 1) /* degenerate case, matrix must be p^0 = 1 */ + return 0; + /* + * c holds the coefficient of P(x) = Prod (x - p_i), i=0..k-1 + * b holds the coefficient for the matrix inversion + */ + c = NEW_GF_MATRIX(1, k); + b = NEW_GF_MATRIX(1, k); + + p = NEW_GF_MATRIX(1, k); + + for (j = 1, i = 0; i < k; i++, j += k) { + c[i] = 0; + p[i] = src[j]; /* p[i] */ + } + /* + * construct coeffs. recursively. We know c[k] = 1 (implicit) + * and start P_0 = x - p_0, then at each stage multiply by + * x - p_i generating P_i = x P_{i-1} - p_i P_{i-1} + * After k steps we are done. + */ + c[k - 1] = p[0]; /* really -p(0), but x = -x in GF(2^m) */ + for (i = 1; i < k; i++) { + gf p_i = p[i]; /* see above comment */ + for (j = k - 1 - (i - 1); j < k - 1; j++) c[j] ^= gf_mul(p_i, c[j + 1]); + c[k - 1] ^= p_i; + } + + for (row = 0; row < k; row++) { + /* + * synthetic division etc. + */ + xx = p[row]; + t = 1; + b[k - 1] = 1; /* this is in fact c[k] */ + for (i = k - 2; i >= 0; i--) { + b[i] = c[i + 1] ^ gf_mul(xx, b[i + 1]); + t = gf_mul(xx, t) ^ b[i]; + } + for (col = 0; col < k; col++) + src[col * k + row] = gf_mul(inverse[t], b[col]); + } + free(c); + free(b); + free(p); + return 0; +} + +static int fec_initialized = 0; +static void init_fec() { + TICK(ticks[0]); + generate_gf(); + TOCK(ticks[0]); + DDB(fprintf(stderr, "generate_gf took %ldus\n", ticks[0]);) + TICK(ticks[0]); + init_mul_table(); + TOCK(ticks[0]); + DDB(fprintf(stderr, "init_mul_table took %ldus\n", ticks[0]);) + fec_initialized = 1; +} + +/* + * This section contains the proper FEC encoding/decoding routines. + * The encoding matrix is computed starting with a Vandermonde matrix, + * and then transforming it into a systematic matrix. + */ + +#define FEC_MAGIC 0xFECC0DEC + +void fec_free(struct fec_parms *p) { + if (p == NULL || p->magic != (((FEC_MAGIC ^ p->k) ^ p->n) ^ + (unsigned long)(p->enc_matrix))) { + fprintf(stderr, "bad parameters to fec_free\n"); + return; + } + free(p->enc_matrix); + free(p); +} + +/* + * create a new encoder, returning a descriptor. This contains k,n and + * the encoding matrix. + */ +struct fec_parms *fec_new(int k, int n) { + int row, col; + gf *p, *tmp_m; + + struct fec_parms *retval; + + if (fec_initialized == 0) init_fec(); + + if (k > GF_SIZE + 1 || n > GF_SIZE + 1 || k > n) { + fprintf(stderr, "Invalid parameters k %d n %d GF_SIZE %d\n", k, n, GF_SIZE); + return NULL; + } + retval = (struct fec_parms *)my_malloc(sizeof(struct fec_parms), "new_code"); + retval->k = k; + retval->n = n; + retval->enc_matrix = NEW_GF_MATRIX(n, k); + retval->magic = ((FEC_MAGIC ^ k) ^ n) ^ (unsigned long)(retval->enc_matrix); + tmp_m = NEW_GF_MATRIX(n, k); + /* + * fill the matrix with powers of field elements, starting from 0. + * The first row is special, cannot be computed with exp. table. + */ + tmp_m[0] = 1; + for (col = 1; col < k; col++) tmp_m[col] = 0; + for (p = tmp_m + k, row = 0; row < n - 1; row++, p += k) { + for (col = 0; col < k; col++) p[col] = gf_exp[modnn(row * col)]; + } + + /* + * quick code to build systematic matrix: invert the top + * k*k vandermonde matrix, multiply right the bottom n-k rows + * by the inverse, and construct the identity matrix at the top. + */ + TICK(ticks[3]); + invert_vdm(tmp_m, k); /* much faster than invert_mat */ + matmul(tmp_m + k * k, tmp_m, retval->enc_matrix + k * k, n - k, k, k); + /* + * the upper matrix is I so do not bother with a slow multiply + */ + bzero(retval->enc_matrix, k * k * sizeof(gf)); + for (p = retval->enc_matrix, col = 0; col < k; col++, p += k + 1) *p = 1; + free(tmp_m); + TOCK(ticks[3]); + + DDB(fprintf(stderr, "--- %ld us to build encoding matrix\n", ticks[3]);) + DEB(pr_matrix(retval->enc_matrix, n, k, "encoding_matrix");) + return retval; +} + +/* + * fec_encode accepts as input pointers to n data packets of size sz, + * and produces as output a packet pointed to by fec, computed + * with index "index". + */ +void fec_encode(struct fec_parms *code, gf *src[], gf *fec, int index, int sz) { + int i, k = code->k; + gf *p; + + if (GF_BITS > 8) sz /= 2; + + if (index < k) + bcopy(src[index], fec, sz * sizeof(gf)); + else if (index < code->n) { + p = &(code->enc_matrix[index * k]); + bzero(fec, sz * sizeof(gf)); + for (i = 0; i < k; i++) addmul(fec, src[i], p[i], sz); + } else + fprintf(stderr, "Invalid index %d (max %d)\n", index, code->n - 1); +} + +/* + * shuffle move src packets in their position + */ +static int shuffle(gf *pkt[], int index[], int k) { + int i; + + for (i = 0; i < k;) { + if (index[i] >= k || index[i] == i) + i++; + else { + /* + * put pkt in the right position (first check for conflicts). + */ + int c = index[i]; + + if (index[c] == c) { + DEB(fprintf(stderr, "\nshuffle, error at %d\n", i);) + return 1; + } + SWAP(index[i], index[c], int); + SWAP(pkt[i], pkt[c], gf *); + } + } + DEB(/* just test that it works... */ + for (i = 0; i < k; i++) { + if (index[i] < k && index[i] != i) { + fprintf(stderr, "shuffle: after\n"); + for (i = 0; i < k; i++) fprintf(stderr, "%3d ", index[i]); + fprintf(stderr, "\n"); + return 1; + } + }) + return 0; +} + +/* + * build_decode_matrix constructs the encoding matrix given the + * indexes. The matrix must be already allocated as + * a vector of k*k elements, in row-major order + */ +static gf *build_decode_matrix(struct fec_parms *code, gf *pkt[], int index[]) { + int i, k = code->k; + gf *p, *matrix = NEW_GF_MATRIX(k, k); + + TICK(ticks[9]); + for (i = 0, p = matrix; i < k; i++, p += k) { +#if 1 /* this is simply an optimization, not very useful indeed */ + if (index[i] < k) { + bzero(p, k * sizeof(gf)); + p[i] = 1; + } else +#endif + if (index[i] < code->n) + bcopy(&(code->enc_matrix[index[i] * k]), p, k * sizeof(gf)); + else { + fprintf(stderr, "decode: invalid index %d (max %d)\n", index[i], + code->n - 1); + free(matrix); + return NULL; + } + } + TICK(ticks[9]); + if (invert_mat(matrix, k)) { + free(matrix); + matrix = NULL; + } + TOCK(ticks[9]); + return matrix; +} + +/* + * fec_decode receives as input a vector of packets, the indexes of + * packets, and produces the correct vector as output. + * + * Input: + * code: pointer to code descriptor + * pkt: pointers to received packets. They are modified + * to store the output packets (in place) + * index: pointer to packet indexes (modified) + * sz: size of each packet + */ +int fec_decode(struct fec_parms *code, gf *pkt[], int index[], int sz) { + gf *m_dec; + gf **new_pkt; + int row, col, k = code->k; + + if (GF_BITS > 8) sz /= 2; + + if (shuffle(pkt, index, k)) /* error if true */ + return 1; + m_dec = build_decode_matrix(code, pkt, index); + + if (m_dec == NULL) return 1; /* error */ + /* + * do the actual decoding + */ + new_pkt = (gf **)my_malloc(k * sizeof(gf *), "new pkt pointers"); + for (row = 0; row < k; row++) { + if (index[row] >= k) { + new_pkt[row] = (gf *)my_malloc(sz * sizeof(gf), "new pkt buffer"); + bzero(new_pkt[row], sz * sizeof(gf)); + for (col = 0; col < k; col++) + addmul(new_pkt[row], pkt[col], m_dec[row * k + col], sz); + } + } + /* + * move pkts to their final destination + */ + for (row = 0; row < k; row++) { + if (index[row] >= k) { + bcopy(new_pkt[row], pkt[row], sz * sizeof(gf)); + free(new_pkt[row]); + } + } + free(new_pkt); + free(m_dec); + + return 0; +} |