From: Steinar H. Gunderson <sesse@debian.org>
Date: Mon, 1 Jun 2009 18:37:35 +0000 (+0200)
Subject: Kill AC_END_OF_BLOCK as well.
X-Git-Url: https://git.sesse.net/?p=fjl;a=commitdiff_plain;h=12195f1ed80bebbfecfa7505ec965177228ea916

Kill AC_END_OF_BLOCK as well.
---

diff --git a/dehuff.c b/dehuff.c
index f08dd88..5574e27 100644
--- a/dehuff.c
+++ b/dehuff.c
@@ -133,9 +133,9 @@ void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void*
 			}
 			if (rs == 0x00) {
 				// End of block.
-				tbl->ac_table_codes[i] = AC_END_OF_BLOCK;
+				tbl->ac_table_codes[i] = 0;
 				tbl->ac_table_length[i] = length;
-				tbl->ac_table_skip[i] = 1;
+				tbl->ac_table_skip[i] = 64;
 				continue;
 			}
 			if (rs == 0xf0) {
diff --git a/dehuff.h b/dehuff.h
index 92c2aff..c54f68a 100644
--- a/dehuff.h
+++ b/dehuff.h
@@ -20,7 +20,6 @@ static const int DEHUF_SLOW_PATH = -1;
 #define DEHUF_AC_TABLE_BITS 10
 #define DEHUF_AC_TABLE_SIZE (1 << DEHUF_AC_TABLE_BITS)
 static const int AC_DEHUF_SLOW_PATH = 0xf0000000;
-static const int AC_END_OF_BLOCK = 0xf0000001;
 
 struct huffman_table {
 	unsigned num_codes[17];     // BITS
diff --git a/driver.c b/driver.c
index f24b0f5..f07e63e 100644
--- a/driver.c
+++ b/driver.c
@@ -116,38 +116,33 @@ 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; ) {
-		possibly_refill(bits, DEHUF_AC_TABLE_BITS);
 		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 (__builtin_expect(code == AC_DEHUF_SLOW_PATH, 0)) {
 			unsigned rs = read_huffman_symbol_no_refill(tbl, bits);
-			unsigned r = rs >> 4;
-			unsigned s = rs & 0xf;
-			i += r + 1;
-			possibly_refill(bits, s);
-
 			if (rs == 0x00) {
 				/* end of block */
 				break;
 			}
-			if (rs == 0xf0) {
-				/* 16 zero coefficients */
-				continue;
-			}
 
+			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 {
-			unsigned length = tbl->ac_table_length[lookup];
-			int r = tbl->ac_table_skip[lookup];
-			assert(r >= 1);
-			i += r;
 			assert(bits->bits_available >= length);
 			read_bits(bits, length);
-			if (code == AC_END_OF_BLOCK) {
-				break;
-			}
+			possibly_refill(bits, DEHUF_AC_TABLE_BITS);
+
+			assert(r >= 1);
+			i += r;
 			coeff[unzigzag[i]] = code;
 		}
 	}
diff --git a/zigzag.h b/zigzag.h
index 3fc1377..5d9df28 100644
--- a/zigzag.h
+++ b/zigzag.h
@@ -4,10 +4,10 @@
 #include "idct.h"
 
 // Table for transforming from zig-zag order to natural order.
-// We use the same trick as libjpeg here; there are 16 extra entries
+// We use the same trick as libjpeg here; there are 64 extra entries
 // after the end of the table, since the run-length decoder could
 // potentially cause entries indices >= 64 to be decoded.
-static const unsigned unzigzag[DCTSIZE2 + 16] = {
+static const unsigned unzigzag[DCTSIZE2 * 2] = {
 	// Regular entries.
 	 0,  1,  8, 16,  9,  2,  3, 10,
 	17, 24, 32, 25, 18, 11,  4,  5,
@@ -18,7 +18,14 @@ static const unsigned unzigzag[DCTSIZE2 + 16] = {
 	58, 59, 52, 45, 38, 31, 39, 46,
 	53, 60, 61, 54, 47, 55, 62, 63,
 
-	// Extra padding entries; should never be referenced in well-formed data.
+	// Extra padding entries.
+	// May get referenced by malformed data or during end-of-block processing.
+	63, 63, 63, 63, 63, 63, 63, 63,
+	63, 63, 63, 63, 63, 63, 63, 63,
+	63, 63, 63, 63, 63, 63, 63, 63,
+	63, 63, 63, 63, 63, 63, 63, 63,
+	63, 63, 63, 63, 63, 63, 63, 63,
+	63, 63, 63, 63, 63, 63, 63, 63,
 	63, 63, 63, 63, 63, 63, 63, 63,
 	63, 63, 63, 63, 63, 63, 63, 63,
 };