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[cover] Optimize case where d <= 8

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Nick Terrell
2017-05-02 11:02:43 -07:00
parent 865918dd04
commit f2d9ef1dc0
3 changed files with 34 additions and 10 deletions
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programs/zstd.1
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@@ -1,5 +1,5 @@
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.TH "ZSTD" "1" "April 2017" "zstd 1.1.5" "User Commands"
.TH "ZSTD" "1" "May 2017" "zstd 1.2.0" "User Commands"
.
.SH "NAME"
\fBzstd\fR \- zstd, zstdmt, unzstd, zstdcat \- Compress or decompress \.zst files
@@ -188,7 +188,7 @@ dictionary selectivity level (default: 9) the smaller the value, the denser the
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.TP
\fB\-\-cover=k#,d=#\fR
Use alternate dictionary builder algorithm named cover with parameters \fIk\fR and \fId\fR with \fId\fR <= \fIk\fR\. Selects segments of size \fIk\fR with the highest score to put in the dictionary\. The score of a segment is computed by the sum of the frequencies of all the subsegments of of size \fId\fR\. Generally \fId\fR should be in the range [6, 24]\. Good values for \fIk\fR vary widely based on the input data, but a safe range is [32, 2048]\.
Use alternate dictionary builder algorithm named cover with parameters \fIk\fR and \fId\fR with \fId\fR <= \fIk\fR\. Selects segments of size \fIk\fR with the highest score to put in the dictionary\. The score of a segment is computed by the sum of the frequencies of all the subsegments of of size \fId\fR\. Generally \fId\fR should be in the range [6, 8], but no more than 24\. When \fId\fR <= 8, the dictionary builder will run significantly faster\. Good values for \fIk\fR vary widely based on the input data, but a safe range is [32, 2048]\.
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.br
Example: \fB\-\-train \-\-cover=k=64,d=8 FILEs\fR\.
programs/zstd.1.md
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@@ -186,7 +186,8 @@ Typical gains range from 10% (at 64KB) to x5 better (at <1KB).
Selects segments of size _k_ with the highest score to put in the dictionary.
The score of a segment is computed by the sum of the frequencies of all the
subsegments of of size _d_.
Generally _d_ should be in the range [6, 24].
Generally _d_ should be in the range [6, 8], but no more than 24.
When _d_ <= 8, the dictionary builder will run significantly faster.
Good values for _k_ vary widely based on the input data,
but a safe range is [32, 2048].<br />
Example: `--train --cover=k=64,d=8 FILEs`.