From: Steinar H. Gunderson <sesse@debian.org>
Date: Mon, 1 Jun 2009 15:36:48 +0000 (+0200)
Subject: Minor optimizations to the new AC coefficient tables.
X-Git-Url: https://git.sesse.net/?p=fjl;a=commitdiff_plain;h=a1596fbb6a92217ff5eb57600b36a9d695ca1ae8

Minor optimizations to the new AC coefficient tables.
---

diff --git a/dehuff.c b/dehuff.c
index 695da0b..50fb53e 100644
--- a/dehuff.c
+++ b/dehuff.c
@@ -123,8 +123,6 @@ 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];
diff --git a/dehuff.h b/dehuff.h
index ec9c976..0f86c3b 100644
--- a/dehuff.h
+++ b/dehuff.h
@@ -15,7 +15,7 @@
 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 12 kB of data to store
+// 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)
@@ -49,8 +49,8 @@ struct huffman_table {
 	// number of bits to skip (_length) and the number of zero coefficients
 	// after this one (_skip).
 	int ac_table_codes[DEHUF_AC_TABLE_SIZE]; 
-	int ac_table_length[DEHUF_AC_TABLE_SIZE]; 
-	int ac_table_skip[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 {
diff --git a/driver.c b/driver.c
index cda257e..c5ae87e 100644
--- a/driver.c
+++ b/driver.c
@@ -120,8 +120,6 @@ void decode_ac_coefficients(const struct huffman_table* tbl, struct bit_source*
 		possibly_refill(bits, DEHUF_AC_TABLE_BITS);
 		unsigned lookup = peek_bits(bits, DEHUF_AC_TABLE_BITS);
 		int code = tbl->ac_table_codes[lookup];
-		int length = tbl->ac_table_length[lookup];
-		int r = tbl->ac_table_skip[lookup];
 
 		assert(length == AC_DEHUF_SLOW_PATH || (length > 0 && length <= DEHUF_AC_TABLE_BITS));
 
@@ -145,6 +143,8 @@ void decode_ac_coefficients(const struct huffman_table* tbl, struct bit_source*
 
 			coeff[unzigzag[i]] = extend(read_bits(bits, s), s);
 		} else {
+			int length = tbl->ac_table_length[lookup];
+			int r = tbl->ac_table_skip[lookup];
 			assert(r >= 0);
 			i += r;
 			assert(bits->bits_available >= length);