From: Steinar H. Gunderson <sesse@debian.org>
Date: Mon, 1 Jun 2009 17:08:00 +0000 (+0200)
Subject: Remove an increment from the fast path of the AC coefficient decoding.
X-Git-Url: https://git.sesse.net/?p=fjl;a=commitdiff_plain;h=bbe665e5ef6a103657f4d921ddd4b540f38daf3d

Remove an increment from the fast path of the AC coefficient decoding.
---

diff --git a/dehuff.c b/dehuff.c
index 50fb53e..8cdc2c8 100644
--- a/dehuff.c
+++ b/dehuff.c
@@ -135,14 +135,14 @@ void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void*
 				// End of block.
 				tbl->ac_table_codes[i] = AC_END_OF_BLOCK;
 				tbl->ac_table_length[i] = length;
-				tbl->ac_table_skip[i] = 0;
+				tbl->ac_table_skip[i] = 1;
 				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;
+				tbl->ac_table_skip[i] = 16;
 				continue;
 			}
 			
@@ -157,7 +157,7 @@ void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void*
 
 			tbl->ac_table_codes[i] = extend(bits, s);
 			tbl->ac_table_length[i] = length + s;
-			tbl->ac_table_skip[i] = r;
+			tbl->ac_table_skip[i] = r + 1;
 
 			assert(tbl->ac_table_length[i] <= DEHUF_AC_TABLE_BITS);
 		}	
diff --git a/driver.c b/driver.c
index 6dcc8b3..fcd9f7f 100644
--- a/driver.c
+++ b/driver.c
@@ -116,7 +116,7 @@ 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)
 {
-	for (unsigned i = 1; i < DCTSIZE2; ++i) {
+	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];
@@ -125,7 +125,7 @@ void decode_ac_coefficients(const struct huffman_table* tbl, struct bit_source*
 			unsigned rs = read_huffman_symbol_no_refill(tbl, bits);
 			unsigned r = rs >> 4;
 			unsigned s = rs & 0xf;
-			i += r;
+			i += r + 1;
 			possibly_refill(bits, s);
 
 			if (rs == 0x00) {
@@ -143,7 +143,7 @@ void decode_ac_coefficients(const struct huffman_table* tbl, struct bit_source*
 		} else {
 			unsigned length = tbl->ac_table_length[lookup];
 			int r = tbl->ac_table_skip[lookup];
-			assert(r >= 0);
+			assert(r >= 1);
 			i += r;
 			assert(bits->bits_available >= length);
 			read_bits(bits, length);