X-Git-Url: https://git.sesse.net/?p=fjl;a=blobdiff_plain;f=dehuff.c;h=695da0bdc78ee2d863cbb0fa547b628619ffc4ab;hp=c4a65eea8a0619153bb9910cd5421db53bd01193;hb=1cfb04470add4e31406785980e7ce14a8e9d0672;hpb=03497d9a2c6de19c6b8a0761b2703ca61b174e2a

diff --git a/dehuff.c b/dehuff.c
index c4a65ee..695da0b 100644
--- a/dehuff.c
+++ b/dehuff.c
@@ -119,6 +119,50 @@ void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void*
 				}
 			}
 		}	
+		
+		// Generate the AC lookup tables.
+		for (unsigned i = 0; i < DEHUF_AC_TABLE_SIZE; ++i) {
+			tbl->ac_table_codes[i] = AC_DEHUF_SLOW_PATH;
+			tbl->ac_table_length[i] = AC_DEHUF_SLOW_PATH;
+			tbl->ac_table_skip[i] = AC_DEHUF_SLOW_PATH;
+
+			int lookup = i >> (DEHUF_AC_TABLE_BITS - DEHUF_TABLE_BITS);
+			int rs = tbl->lookup_table_codes[lookup];
+			unsigned length = tbl->lookup_table_length[lookup];
+			if (rs == DEHUF_SLOW_PATH) {
+				// Not enough bits to decode even the length.
+				continue;
+			}
+			if (rs == 0x00) {
+				// End of block.
+				tbl->ac_table_codes[i] = AC_END_OF_BLOCK;
+				tbl->ac_table_length[i] = length;
+				tbl->ac_table_skip[i] = 0;
+				continue;
+			}
+			if (rs == 0xf0) {
+				// 16 zero coefficients.
+				tbl->ac_table_codes[i] = AC_SIXTEEN_ZEROS;
+				tbl->ac_table_length[i] = length;
+				tbl->ac_table_skip[i] = 15;
+				continue;
+			}
+			
+			unsigned r = rs >> 4;
+			unsigned s = rs & 0xf;
+			if (s > DEHUF_AC_TABLE_BITS - length) {
+				// Not enough bits to decode this coefficient.
+				continue;
+			}
+
+			unsigned bits = (i >> (DEHUF_AC_TABLE_BITS - length - s)) & ((1 << s) - 1);
+
+			tbl->ac_table_codes[i] = extend(bits, s);
+			tbl->ac_table_length[i] = length + s;
+			tbl->ac_table_skip[i] = r;
+
+			assert(tbl->ac_table_length[i] <= DEHUF_AC_TABLE_BITS);
+		}	
 	}
 
 	free(buf);