Increase maximum window size

* Maximum window size in 32-bit mode is 1GB, since allocations for 2GB fail
  on my Mac.
* Maximum window size in 64-bit mode is 2GB, since that is the largest
  power of 2 that works with the overflow prevention.
* Allow `--long=windowLog` to set the window log, along with
  `--zstd=wlog=#`. These options also set the window size during
  decompression, but don't override `--memory=#` if it is set.
* Present a helpful error message when the window size is too large during
  decompression.
* The long range matcher defaults to a hash log 7 less than the window log,
  which keeps it at 20 for window log 27.
* Keep the default long range matcher window size and the default maximum
  window size at 27 for the API and CLI.
* Add tests that use the maximum window size and hash size for compression
  and decompression.
This commit is contained in:
Nick Terrell
2017-09-26 14:00:01 -07:00
parent 8a4d0abc1c
commit c233bdbaee
12 changed files with 139 additions and 40 deletions
+14 -4
View File
@@ -104,8 +104,11 @@ Display information related to a zstd compressed file, such as size, ratio, and
unlocks high compression levels 20+ (maximum 22), using a lot more memory\. Note that decompression will also require more memory when using these levels\.
.
.TP
\fB\-\-long\fR
enables long distance matching\. This increases the window size (\fBwindowLog\fR) and memory usage for both the compressor and decompressor\. This setting is designed to improve the compression ratio for files with long matches at a large distance (up to the maximum window size, 128 MiB)\.
\fB\-\-long[=#]\fR
enables long distance matching with \fB#\fR \fBwindowLog\fR, if not \fB#\fR is not present it defaults to \fB27\fR\. This increases the window size (\fBwindowLog\fR) and memory usage for both the compressor and decompressor\. This setting is designed to improve the compression ratio for files with long matches at a large distance\.
.
.IP
Note: If \fBwindowLog\fR is set to larger than 27, \fB\-\-long=windowLog\fR or \fB\-\-memory=windowSize\fR needs to be passed to the decompressor\.
.
.TP
\fB\-T#\fR, \fB\-\-threads=#\fR
@@ -190,6 +193,10 @@ Dictionary saved into \fBfile\fR (default name: dictionary)\.
Limit dictionary to specified size (default: 112640)\.
.
.TP
\fB\-B#\fR
Split input files in blocks of size # (default: no split)
.
.TP
\fB\-\-dictID=#\fR
A dictionary ID is a locally unique ID that a decoder can use to verify it is using the right dictionary\. By default, zstd will create a 4\-bytes random number ID\. It\'s possible to give a precise number instead\. Short numbers have an advantage : an ID < 256 will only need 1 byte in the compressed frame header, and an ID < 65536 will only need 2 bytes\. This compares favorably to 4 bytes default\. However, it\'s up to the dictionary manager to not assign twice the same ID to 2 different dictionaries\.
.
@@ -267,7 +274,10 @@ There are 8 strategies numbered from 1 to 8, from faster to stronger: 1=ZSTD_fas
Specify the maximum number of bits for a match distance\.
.
.IP
The higher number of increases the chance to find a match which usually improves compression ratio\. It also increases memory requirements for the compressor and decompressor\. The minimum \fIwlog\fR is 10 (1 KiB) and the maximum is 27 (128 MiB)\.
The higher number of increases the chance to find a match which usually improves compression ratio\. It also increases memory requirements for the compressor and decompressor\. The minimum \fIwlog\fR is 10 (1 KiB) and the maximum is 30 (1 GiB) on 32\-bit platforms and 31 (2 GiB) on 64\-bit platforms\.
.
.IP
Note: If \fBwindowLog\fR is set to larger than 27, \fB\-\-long=windowLog\fR or \fB\-\-memory=windowSize\fR needs to be passed to the decompressor\.
.
.TP
\fBhashLog\fR=\fIhlog\fR, \fBhlog\fR=\fIhlog\fR
@@ -340,7 +350,7 @@ Bigger hash tables usually improve compression ratio at the expense of more memo
The minimum \fIldmhlog\fR is 6 and the maximum is 26 (default: 20)\.
.
.TP
\fBldmSearchLength\fR=\fIldmslen\fR, \fBldmSlen\fR=\fIldmslen\fR
\fBldmSearchLength\fR=\fIldmslen\fR, \fBldmslen\fR=\fIldmslen\fR
Specify the minimum searched length of a match for long distance matching\.
.
.IP