X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=bitstream.c;h=ee25fffaf2fed5853a3b4c38d8dddedb4dfb41d8;hb=b35708a83afe82b18251d53343519dd41e6e80f6;hp=dedcdead5bc77bb12880ec9342dc95a39e6cd615;hpb=d06e0fc014b8557556951a78ae4c07b5bba2052f;p=paraslash.git

diff --git a/bitstream.c b/bitstream.c
index dedcdead..ee25fffa 100644
--- a/bitstream.c
+++ b/bitstream.c
@@ -27,6 +27,7 @@
 #include "wma.h"
 #include "bitstream.h"
 
+/** Read an 8, 16, or 32 bit entity from a VLC table. */
 #define GET_DATA(v, table, i, size) \
 {\
 	const uint8_t *ptr = (const uint8_t *)table + i * size; \
@@ -57,8 +58,7 @@ static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
 		const void *bits, const void *codes, int codes_size,
 		uint32_t code_prefix, int n_prefix)
 {
-	int i, j, k, n, table_size, table_index, nb, n1, idx, code_prefix2,
-		symbol;
+	int i, j, k, n, table_size, table_index, nb, n1, idx, code_prefix2;
 	uint32_t code;
 	VLC_TYPE(*table)[2];
 
@@ -68,18 +68,17 @@ static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
 	table = &vlc->table[table_index];
 
 	for (i = 0; i < table_size; i++) {
-		table[i][1] = 0;	//bits
-		table[i][0] = -1;	//codes
+		table[i][1] = 0; /* bits */
+		table[i][0] = -1; /* codes */
 	}
 
-	/* map codes and compute auxillary table sizes */
+	/* map codes and compute auxiliary table sizes */
 	for (i = 0; i < nb_codes; i++) {
 		GET_DATA(n, bits, i, 1);
 		GET_DATA(code, codes, i, codes_size);
 		/* we accept tables with holes */
 		if (n <= 0)
 			continue;
-		symbol = i;
 		/* if code matches the prefix, it is in the table */
 		n -= n_prefix;
 		code_prefix2 = code >> n;
@@ -94,36 +93,36 @@ static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
 					PARA_EMERG_LOG("incorrect code\n");
 					exit(EXIT_FAILURE);
 				}
-				table[j][1] = n;	//bits
-				table[j][0] = symbol;
+				table[j][1] = n; /* bits */
+				table[j][0] = i;
 				j++;
 			}
 		} else {
 			n -= table_nb_bits;
 			j = (code >> n) & ((1 << table_nb_bits) - 1);
 			/* compute table size */
-			n1 = -table[j][1];	//bits
+			n1 = -table[j][1]; /* bits */
 			if (n > n1)
 				n1 = n;
-			table[j][1] = -n1;	//bits
+			table[j][1] = -n1; /* bits */
 		}
 	}
 
-	/* fill auxillary tables recursively */
+	/* fill auxiliary tables recursively */
 	for (i = 0; i < table_size; i++) {
-		n = table[i][1];	//bits
+		n = table[i][1]; /* bits */
 		if (n < 0) {
 			n = -n;
 			if (n > table_nb_bits) {
 				n = table_nb_bits;
-				table[i][1] = -n;	//bits
+				table[i][1] = -n; /* bits */
 			}
 			idx = build_table(vlc, n, nb_codes, bits, codes,
 				codes_size, (code_prefix << table_nb_bits) | i,
 				n_prefix + table_nb_bits);
 			/* vlc->table might have changed */
 			table = &vlc->table[table_index];
-			table[i][0] = idx;	//code
+			table[i][0] = idx; /* code */
 		}
 	}
 	return table_index;
@@ -132,10 +131,11 @@ static int build_table(struct vlc *vlc, int table_nb_bits, int nb_codes,
 /**
  * Build VLC decoding tables suitable for use with get_vlc().
  *
- * \param nb_bits Set the decoding table size (2^nb_bits)
- * entries. The bigger it is, the faster is the decoding. But
- * it should not be too big to save memory and L1 cache. '9'
- * is a good compromise.
+ * \param vlc The structure to be initialized.
+ *
+ * \param nb_bits Set the decoding table size (2^nb_bits) entries. The bigger
+ * it is, the faster is the decoding. But it should not be too big to save
+ * memory and L1 cache. '9' is a good compromise.
  *
  * \param nb_codes Number of vlcs codes.
  *
@@ -159,7 +159,56 @@ void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
 	build_table(vlc, nb_bits, nb_codes, bits, codes, codes_size, 0, 0);
 }
 
+/**
+ * Deallocate all resources of a VLC table.
+ *
+ * \param vlc Pointer to an initialized vlc structure.
+ *
+ * The table given by \a vlc must have been initialized earlier via \ref
+ * init_vlc().
+ */
 void free_vlc(struct vlc *vlc)
 {
 	freep(&vlc->table);
 }
+
+/**
+ * Parse a vlc code.
+ *
+ * \param gbc The getbit context structure.
+ *
+ * \param table The vlc tables to use.
+ *
+ * \param bits The number of bits which will be read at once, must be
+ * identical to nb_bits in init_vlc().
+ *
+ * \param max_depth The number of times bits bits must be read to completely
+ * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
+ *
+ * \return The vlc code.
+ */
+int get_vlc(struct getbit_context *gbc, VLC_TYPE(*table)[2], int bits,
+		int max_depth)
+{
+	int n, idx, nb_bits, code;
+
+	idx = show_bits(gbc, bits);
+	code = table[idx][0];
+	n = table[idx][1];
+	if (max_depth > 1 && n < 0) {
+		skip_bits(gbc, bits);
+		nb_bits = -n;
+		idx = show_bits(gbc, nb_bits) + code;
+		code = table[idx][0];
+		n = table[idx][1];
+		if (max_depth > 2 && n < 0) {
+			skip_bits(gbc, nb_bits);
+			nb_bits = -n;
+			idx = show_bits(gbc, nb_bits) + code;
+			code = table[idx][0];
+			n = table[idx][1];
+		}
+	}
+	skip_bits(gbc, n);
+	return code >= 0? code : -E_VLC;
+}