#define DEHUF_TABLE_SIZE (1 << DEHUF_TABLE_BITS)
static const int DEHUF_SLOW_PATH = -1;
+// About 98% of all AC coefficients (control byte + coefficient) are <= 10 bits
+// long; again, see codelen.txt. This will cost us about 6 kB of data to store
+// in L1 cache.
+#define DEHUF_AC_TABLE_BITS 10
+#define DEHUF_AC_TABLE_SIZE (1 << DEHUF_AC_TABLE_BITS)
+static const int AC_DEHUF_SLOW_PATH = 0xf0000000;
+
struct huffman_table {
unsigned num_codes[17]; // BITS
unsigned char codes[256]; // HUFFVAL
// the lookup tables is int to avoid extra zero extending.
int lookup_table_codes[DEHUF_TABLE_SIZE];
int lookup_table_length[DEHUF_TABLE_SIZE];
+
+ // Further lookup tables for decoding AC coefficients.
+ // (Generated but obviously not used for DC coefficients.)
+ // Maps from 10-bit lookahead values to the signed coeffient (_codes),
+ // number of bits to skip (_length) and the number of zero coefficients
+ // after this one (_skip).
+ int ac_table_codes[DEHUF_AC_TABLE_SIZE];
+ uint8_t ac_table_length[DEHUF_AC_TABLE_SIZE];
+ uint8_t ac_table_skip[DEHUF_AC_TABLE_SIZE];
};
enum coefficient_class {