X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=fec.c;h=2301cc8d2d4653b8bc82a8bcc46b5867b5d7af14;hp=f3e68454941e702ff7cb9ca78ca9a3b749998086;hb=0cbd0ac87ebe208b0d47df28e86c16886bdb687d;hpb=4a96cfc150f797745c054bd5516e80079bdf52a8

diff --git a/fec.c b/fec.c
index f3e68454..2301cc8d 100644
--- a/fec.c
+++ b/fec.c
@@ -1,5 +1,6 @@
+/** \file fec.c Forward error correction based on Vandermonde matrices. */
+
 /*
- * fec.c -- forward error correction based on Vandermonde matrices
  * 980624
  * (C) 1997-98 Luigi Rizzo (luigi@iet.unipi.it)
  *
@@ -32,30 +33,48 @@
  * OF SUCH DAMAGE.
  */
 
+#include <regex.h>
+
 #include "para.h"
 #include "error.h"
 #include "portable_io.h"
 #include "string.h"
 #include "fec.h"
 
-#define GF_BITS  8 /* code over GF(256) */
+/** Code over GF(256). */
+#define GF_BITS  8
+/** The largest number in GF(256) */
 #define	GF_SIZE ((1 << GF_BITS) - 1)
 
 /*
  * To speed up computations, we have tables for logarithm, exponent and inverse
- * of a number. 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!). The macro gf_mul(x,y) takes care of multiplications.
+ * of a number.
+ */
+
+/** Index->poly form conversion table. */
+static unsigned char gf_exp[2 * GF_SIZE];
+
+/** Poly->index form conversion table. */
+static int gf_log[GF_SIZE + 1];
+
+/** Inverse of a field element. */
+static unsigned char inverse[GF_SIZE + 1];
+
+/**
+ * The multiplication table.
+ *
+ * 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 and put into a ROM.
+ *
+ * \sa \ref gf_mul.
  */
-static unsigned char gf_exp[2 * GF_SIZE]; /* index->poly form conversion table */
-static int gf_log[GF_SIZE + 1];	/* Poly->index form conversion table    */
-static unsigned char inverse[GF_SIZE + 1]; /* inverse of field elem. */
 static unsigned char gf_mul_table[GF_SIZE + 1][GF_SIZE + 1];
-/* Multiply two numbers. */
+
+/** Multiply two GF numbers. */
 #define gf_mul(x,y) gf_mul_table[x][y]
 
 /* Compute x % GF_SIZE without a slow divide. */
-static inline unsigned char modnn(int x)
+__a_const static inline unsigned char modnn(int x)
 {
 	while (x >= GF_SIZE) {
 		x -= GF_SIZE;
@@ -151,21 +170,27 @@ static void generate_gf(void)
 		inverse[i] = gf_exp[GF_SIZE - gf_log[i]];
 }
 
+/** How often the loop is unrolled. */
+#define UNROLL 16
+
 /*
  * Compute dst[] = dst[] + c * src[]
  *
  * This is used often, so better optimize it! Currently the loop is unrolled 16
  * times. The case c=0 is also optimized, whereas c=1 is not.
  */
-#define UNROLL 16
-static void addmul(unsigned char *dst1, const unsigned char const *src1,
+static void addmul(unsigned char *dst1, const unsigned char *src1,
 	unsigned char c, int sz)
 {
+	unsigned char *dst, *lim, *col;
+	const unsigned char *src = src1;
+
 	if (c == 0)
 		return;
-	unsigned char *dst = dst1, *lim = &dst[sz - UNROLL + 1],
-		*col = gf_mul_table[c];
-	const unsigned char const *src = src1;
+
+	dst = dst1;
+	lim = &dst[sz - UNROLL + 1];
+	col = gf_mul_table[c];
 
 	for (; dst < lim; dst += UNROLL, src += UNROLL) {
 		dst[0] ^= col[src[0]];
@@ -208,13 +233,14 @@ static void matmul(unsigned char *a, unsigned char *b, unsigned char *c,
 	}
 }
 
+/** Swap two numbers. */
 #define FEC_SWAP(a,b) {typeof(a) tmp = a; a = b; b = tmp;}
 
 /*
  * Compute the inverse of a matrix.
  *
  * k is the size of the matrix 'src' (Gauss-Jordan, adapted from Numerical
- * Recipes in C). Returns -1 if 'src' is singular.
+ * Recipes in C). Returns negative on errors.
  */
 static int invert_mat(unsigned char *src, int k)
 {