aboutsummaryrefslogtreecommitdiff
path: root/huffman.c
diff options
context:
space:
mode:
authorJulian Seward <jseward@acm.org>2005-02-15 22:13:13 +0100
committerJulian Seward <jseward@acm.org>2005-02-15 22:13:13 +0100
commit4d540bfc95a4b0eefc1d1f388ec33534aaeb3a2f (patch)
tree3b7e9c650b4c61d114e1716c4698e40d5c8d7ef7 /huffman.c
parent099d844292f60f9d58914da29e5773204dc55e7a (diff)
downloadbzip2-4d540bfc95a4b0eefc1d1f388ec33534aaeb3a2f.tar.gz
bzip2-4d540bfc95a4b0eefc1d1f388ec33534aaeb3a2f.tar.bz2
bzip2-4d540bfc95a4b0eefc1d1f388ec33534aaeb3a2f.zip
bzip2-1.0.3bzip2-1.0.3
Diffstat (limited to 'huffman.c')
-rw-r--r--huffman.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/huffman.c b/huffman.c
index 293095c..5bf190b 100644
--- a/huffman.c
+++ b/huffman.c
@@ -8,7 +8,7 @@
8 This file is a part of bzip2 and/or libbzip2, a program and 8 This file is a part of bzip2 and/or libbzip2, a program and
9 library for lossless, block-sorting data compression. 9 library for lossless, block-sorting data compression.
10 10
11 Copyright (C) 1996-2002 Julian R Seward. All rights reserved. 11 Copyright (C) 1996-2005 Julian R Seward. All rights reserved.
12 12
13 Redistribution and use in source and binary forms, with or without 13 Redistribution and use in source and binary forms, with or without
14 modification, are permitted provided that the following conditions 14 modification, are permitted provided that the following conditions
@@ -42,7 +42,7 @@
42 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 42 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
43 43
44 Julian Seward, Cambridge, UK. 44 Julian Seward, Cambridge, UK.
45 jseward@acm.org 45 jseward@bzip.org
46 bzip2/libbzip2 version 1.0 of 21 March 2000 46 bzip2/libbzip2 version 1.0 of 21 March 2000
47 47
48 This program is based on (at least) the work of: 48 This program is based on (at least) the work of:
@@ -162,7 +162,24 @@ void BZ2_hbMakeCodeLengths ( UChar *len,
162 162
163 if (! tooLong) break; 163 if (! tooLong) break;
164 164
165 for (i = 1; i < alphaSize; i++) { 165 /* 17 Oct 04: keep-going condition for the following loop used
166 to be 'i < alphaSize', which missed the last element,
167 theoretically leading to the possibility of the compressor
168 looping. However, this count-scaling step is only needed if
169 one of the generated Huffman code words is longer than
170 maxLen, which up to and including version 1.0.2 was 20 bits,
171 which is extremely unlikely. In version 1.0.3 maxLen was
172 changed to 17 bits, which has minimal effect on compression
173 ratio, but does mean this scaling step is used from time to
174 time, enough to verify that it works.
175
176 This means that bzip2-1.0.3 and later will only produce
177 Huffman codes with a maximum length of 17 bits. However, in
178 order to preserve backwards compatibility with bitstreams
179 produced by versions pre-1.0.3, the decompressor must still
180 handle lengths of up to 20. */
181
182 for (i = 1; i <= alphaSize; i++) {
166 j = weight[i] >> 8; 183 j = weight[i] >> 8;
167 j = 1 + (j / 2); 184 j = 1 + (j / 2);
168 weight[i] = j << 8; 185 weight[i] = j << 8;