#include <stdint.h>
#include <sys/types.h>
-// A function to read bytes from some input source. The bytes should be
-// already unstuffed (and thus without markers).
-// A return value of -1 indicates error, a return value of 0 indicates EOF.
-typedef ssize_t (raw_input_func_t)(void*, uint8_t*, size_t);
+#include "bytesource.h"
+#include "bitsource.h"
+
+// About 99% of all Huffman codes are <= 8 bits long (see codelen.txt),
+// and it's what libjpeg uses. Thus, it seems like a reasonable size.
+#define DEHUF_TABLE_BITS 8
+#define DEHUF_TABLE_SIZE (1 << DEHUF_TABLE_BITS)
+static const int DEHUF_SLOW_PATH = -1;
struct huffman_table {
unsigned num_codes[17]; // BITS
int maxcode[16];
int mincode[16];
unsigned valptr[16];
+
+ // Lookup table for fast decoding; given eight bits,
+ // return the symbol and length in bits. For longer codes,
+ // DEHUF_SLOW_PATH is returned.
+
+ // Note that the codes we return are 8-bit, but the type of
+ // the lookup tables is int to avoid extra zero extending.
+ int lookup_table_codes[DEHUF_TABLE_SIZE];
+ int lookup_table_length[DEHUF_TABLE_SIZE];
};
enum coefficient_class {
};
typedef struct huffman_table huffman_tables_t[NUM_COEFF_CLASSES][4];
-void read_huffman_tables(huffman_tables_t* dst, raw_input_func_t* input_func, void* userdata);
+// Read Huffman tables from a stream, and compute the derived values.
+void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void* userdata);
+
+unsigned read_huffman_symbol_slow_path(const struct huffman_table* table,
+ struct bit_source* source);
+
+static inline unsigned read_huffman_symbol_no_refill(
+ const struct huffman_table* table,
+ struct bit_source* source)
+{
+ assert(source->bits_available >= DEHUF_TABLE_BITS);
+ unsigned lookup = peek_bits(source, DEHUF_TABLE_BITS);
+ int code = table->lookup_table_codes[lookup];
+ int length = table->lookup_table_length[lookup];
+
+ if (code == DEHUF_SLOW_PATH) {
+ return read_huffman_symbol_slow_path(table, source);
+ }
+
+ read_bits(source, length);
+ return code;
+}
+
+static inline unsigned read_huffman_symbol(const struct huffman_table* table,
+ struct bit_source* source)
+{
+ possibly_refill(source, DEHUF_TABLE_BITS);
+ return read_huffman_symbol_no_refill(table, source);
+}
+
+// procedure EXTEND (figure F.12)
+
+// Fast lookup table for (1 << (bits - 1)).
+// The table actually helps, since the load can go in parallel with the shift
+// operation below.
+static const int bit_thresholds[16] = {
+ 0, 1 << 0, 1 << 1, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7, 1 << 8, 1 << 9, 1 << 10, 1 << 11, 1 << 12, 1 << 13, 1 << 14
+};
+
+static inline unsigned extend(int val, int bits)
+{
+ if (val < bit_thresholds[bits]) {
+ return val + (-1 << bits) + 1;
+ } else {
+ return val;
+ }
+}
#endif /* !defined(_DEHUFF_H) */