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authorLasse Collin <lasse.collin@tukaani.org>2008-03-22 00:57:33 +0200
committerLasse Collin <lasse.collin@tukaani.org>2008-03-22 00:57:33 +0200
commit63b74d000eedaebb8485f623e56864ff5ab71064 (patch)
tree6cdee417634eabd515282882783eeda0322178e4 /src/liblzma/lzma/lzma_common.h
parentFix data corruption in LZMA encoder. Note that this bug was (diff)
downloadxz-63b74d000eedaebb8485f623e56864ff5ab71064.tar.xz
Demystified the "state" variable in LZMA code. Use the
word literal instead of char for better consistency. There are still some names with _char instead of _literal in lzma_optimum, these may be changed later. Renamed length coder variables. This commit doesn't change the program logic.
Diffstat (limited to '')
-rw-r--r--src/liblzma/lzma/lzma_common.h69
1 files changed, 52 insertions, 17 deletions
diff --git a/src/liblzma/lzma/lzma_common.h b/src/liblzma/lzma/lzma_common.h
index 2bb73157..f677fcce 100644
--- a/src/liblzma/lzma/lzma_common.h
+++ b/src/liblzma/lzma/lzma_common.h
@@ -31,8 +31,6 @@
///////////////
#define REP_DISTANCES 4
-#define STATES 12
-#define LIT_STATES 7
#define POS_SLOT_BITS 6
#define DICT_LOG_SIZE_MAX 30
@@ -105,25 +103,62 @@
// State //
///////////
-// Used for updating strm->data->state in both encoder and decoder.
+/// This enum is used to track which events have occurred most recently and
+/// in which order. This information is used to predict the next event.
+///
+/// Events:
+/// - Literal: One 8-bit byte
+/// - Match: Repeat a chunk of data at some distance
+/// - Long repeat: Multi-byte match at a recently seen distance
+/// - Short repeat: One-byte repeat at a recently seen distance
+///
+/// The event names are in from STATE_oldest_older_previous. REP means
+/// either short or long repeated match, and NONLIT means any non-literal.
+typedef enum {
+ STATE_LIT_LIT,
+ STATE_MATCH_LIT_LIT,
+ STATE_REP_LIT_LIT,
+ STATE_SHORTREP_LIT_LIT,
+ STATE_MATCH_LIT,
+ STATE_REP_LIT,
+ STATE_SHORTREP_LIT,
+ STATE_LIT_MATCH,
+ STATE_LIT_LONGREP,
+ STATE_LIT_SHORTREP,
+ STATE_NONLIT_MATCH,
+ STATE_NONLIT_REP,
+} lzma_lzma_state;
+
+
+/// Total number of states
+#define STATES 12
+
+/// The lowest 7 states indicate that the previous state was a literal.
+#define LIT_STATES 7
+
-#define update_char(index) \
- index = ((index) < 4 \
- ? 0 \
- : ((index) < 10 \
- ? (index) - 3 \
- : (index) - 6))
+/// Indicate that the latest state was a literal.
+#define update_literal(state) \
+ state = ((state) <= STATE_SHORTREP_LIT_LIT \
+ ? STATE_LIT_LIT \
+ : ((state) <= STATE_LIT_SHORTREP \
+ ? (state) - 3 \
+ : (state) - 6))
-#define update_match(index) \
- index = ((index) < LIT_STATES ? 7 : 10)
+/// Indicate that the latest state was a match.
+#define update_match(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH)
-#define update_rep(index) \
- index = ((index) < LIT_STATES ? 8 : 11)
+/// Indicate that the latest state was a long repeated match.
+#define update_long_rep(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP)
-#define update_short_rep(index) \
- index = ((index) < LIT_STATES ? 9 : 11)
+/// Indicate that the latest state was a short match.
+#define update_short_rep(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP)
-#define is_char_state(index) \
- ((index) < LIT_STATES)
+/// Test if the previous state was a literal.
+#define is_literal_state(state) \
+ ((state) < LIT_STATES)
#endif