#include <stdint.h>
#include <sys/types.h>
-#include "input.h"
+#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_SIZE (1 << DEHUF_TABLE_BITS)
static const int DEHUF_SLOW_PATH = -1;
-// 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);
-
struct huffman_table {
unsigned num_codes[17]; // BITS
unsigned char codes[256]; // HUFFVAL
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)
+static inline unsigned read_huffman_symbol_no_refill(
+ 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;
}
+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, unsigned bits)
+{
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+ // GCC should ideally be able to figure out that the conditional move is better, but
+ // it doesn't for various reasons, and this is pretty important for speed, so we hardcode.
+ asm("cmp %2, %0 ; cmovl %3, %0"
+ : "=r" (val)
+ : "0" (val),
+ "g" (bit_thresholds[bits]),
+ "r" (val + (-1 << bits) + 1)
+ : "cc");
+ return val;
+#else
+ if (val < bit_thresholds[bits]) {
+ return val + (-1 << bits) + 1;
+ } else {
+ return val;
+ }
+#endif
+}
+
#endif /* !defined(_DEHUFF_H) */