X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;ds=sidebyside;f=driver.c;h=dfa61ddde0ab2b70e56b8fc924ddd96012db01c7;hb=90f4ece295b2ba5f9b3f36ea8547e65bea1e85f6;hp=616b613f944ee5ae3ba12a69476eb37d9b20a336;hpb=fb0138d517d723f43221e95bd8ece7419dac70b7;p=fjl

diff --git a/driver.c b/driver.c
index 616b613..dfa61dd 100644
--- a/driver.c
+++ b/driver.c
@@ -114,6 +114,40 @@ void read_sof(struct byte_source* source, struct jpeg_image* image)
 	}
 }
 
+void decode_ac_coefficients(const struct huffman_table* tbl, struct bit_source* bits, int16_t* coeff)
+{
+	possibly_refill(bits, DEHUF_AC_TABLE_BITS);
+	for (unsigned i = 0; i < DCTSIZE2 - 1; ) {
+		unsigned lookup = peek_bits(bits, DEHUF_AC_TABLE_BITS);
+		int code = tbl->ac_table_codes[lookup];
+		unsigned length = tbl->ac_table_length[lookup];
+		unsigned r = tbl->ac_table_skip[lookup];
+
+		if (code == AC_DEHUF_SLOW_PATH) {
+			unsigned rs = read_huffman_symbol_no_refill(tbl, bits);
+			if (rs == 0x00) {
+				/* end of block */
+				break;
+			}
+
+			unsigned r = rs >> 4;
+			unsigned s = rs & 0xf;
+			i += r + 1;
+			possibly_refill(bits, s);
+			coeff[unzigzag[i]] = extend(read_bits(bits, s), s);
+			possibly_refill(bits, DEHUF_AC_TABLE_BITS);
+		} else {
+			assert(bits->bits_available >= length);
+			read_bits(bits, length);
+			possibly_refill(bits, DEHUF_AC_TABLE_BITS);
+
+			assert(r >= 1);
+			i += r;
+			coeff[unzigzag[i]] = code;
+		}
+	}
+}
+
 void read_scan(struct byte_source* source, struct jpeg_image* image, huffman_tables_t* tables)
 {
 	unsigned len = read_uint16(byte_source_input_func, source);
@@ -169,34 +203,13 @@ void read_scan(struct byte_source* source, struct jpeg_image* image, huffman_tab
 
 					// decode DC component
 					unsigned dc_category = read_huffman_symbol(dc_table, &bits);
-					possibly_refill(&bits, dc_category + DEHUF_TABLE_BITS);
+					possibly_refill(&bits, dc_category);
 					last_dc[c] += extend(read_bits(&bits, dc_category), dc_category);
 					
 					int16_t coeff[DCTSIZE2] = { 0 };
 					coeff[0] = last_dc[c];
+					decode_ac_coefficients(ac_table, &bits, coeff);
 
-					// decode AC components
-					for (unsigned i = 1; i < DCTSIZE2; ++i) {
-						unsigned rs = read_huffman_symbol_no_refill(ac_table, &bits);
-						unsigned r = rs >> 4;
-						unsigned s = rs & 0xf;
-
-						if (rs == 0x00) {
-							/* end of block */
-							break;
-						}
-						if (rs == 0xf0) {
-							/* 16 zero coefficients */
-							possibly_refill(&bits, DEHUF_TABLE_BITS);
-							i += 15;
-							continue;
-						}
-						i += r;
-
-						possibly_refill(&bits, s + DEHUF_TABLE_BITS);
-						coeff[unzigzag[i]] = extend(read_bits(&bits, s), s);
-					}
-			
 					uint8_t pixdata[DCTSIZE2];	
 					idct_choice(coeff, image->idct_data[image->qtable[cn]], pixdata);