#include <sys/types.h>
#include "bytesource.h"
-#include "input.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.
typedef struct huffman_table huffman_tables_t[NUM_COEFF_CLASSES][4];
// Read Huffman tables from a stream, and compute the derived values.
-void read_huffman_tables(huffman_tables_t* dst, raw_input_func_t* input_func, void* userdata);
+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);
-#include <stdio.h>
-
static inline unsigned read_huffman_symbol(const struct huffman_table* table,
struct bit_source* source)
{
- // FIXME: We can read past the end of the stream here in some edge
- // cases. We need to define some guarantees in the layers above.
possibly_refill(source, DEHUF_TABLE_BITS);
+ 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;
}
+// 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) */