Zstandard![](/ext.png)
or
zstd is a fast compression algorithm developed by
Yann Collet![](/ext.png)
(also known for
LZ4 and
xxHash). It is implemented as a
C library. Zstandard is notable for compressing data at least twice as fast as
zlib with comparable compression ratios.
Using Zstandard from Tcl edit
The following code provides
libzstd bindings for Tcl through
Critcl.
Download it with
wiki-reaper:
wiki-reaper 48788 0 > zstd-0.1.5.tm Code
# Zstandard bindings/demo for Tcl.
# Copyright (c) 2017, 2018 dbohdan.
# License: MIT.
# If you installed libzstd.so.1 to /usr/local/lib/ on *nix, you may need to
# run Tcl with /usr/local/lib/ in $LD_LIBRARY_PATH. E.g.,
# $ LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/usr/local/lib" tclsh zstd.tcl
# in the POSIX shell or
# > env "LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib" tclsh zstd.tcl
# in fish.
package require critcl 3.1.10
if {![critcl::compiling]} {
error {critcl found no compiler}
}
namespace eval zstd {
variable bindingsVersion 0.1.6
variable version {}
}
critcl::ccode {
#include <zstd.h>
}
critcl::clibraries -lzstd
critcl::cinit {
int version = ZSTD_versionNumber();
char s[32];
Tcl_CreateNamespace(ip, "zstd", NULL, NULL);
sprintf(s, "%d.%d.%d", version / 10000, version / 100 % 100, version % 100);
Tcl_SetVar2Ex(ip, "zstd::version", NULL, Tcl_NewStringObj(s, -1), 0);
} {}
critcl::ccommand zstd::compress {cdata interp objc objv} {
int level = 1;
int max_level = ZSTD_maxCLevel();
void *source_buf;
void *dest_buf;
int source_len;
size_t dest_size;
size_t compressed_size;
if (objc != 2 && objc != 3) {
Tcl_WrongNumArgs(interp, 1, objv, "data ?level?");
return TCL_ERROR;
}
if (objc == 3) {
int rc = Tcl_GetIntFromObj(interp, objv[2], &level);
if (rc != TCL_OK || ((level < 1) || (level > max_level))) {
Tcl_SetObjResult(interp,
Tcl_ObjPrintf("level must be integer between "
"1 and %d", max_level));
return TCL_ERROR;
}
}
source_buf = (void *)Tcl_GetByteArrayFromObj(objv[1], &source_len);
dest_size = ZSTD_compressBound(source_len);
dest_buf = malloc(dest_size);
if (dest_buf == NULL) {
Tcl_SetObjResult(interp,
Tcl_NewStringObj("can't allocate memory to compress "
"data", -1));
return TCL_ERROR;
}
compressed_size = ZSTD_compress(dest_buf, dest_size, source_buf,
source_len, level);
if (ZSTD_isError(compressed_size)) {
Tcl_SetObjResult(interp,
Tcl_ObjPrintf("zstd encoding error: %s",
ZSTD_getErrorName(compressed_size)));
return TCL_ERROR;
}
Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(dest_buf, compressed_size));
free(dest_buf);
return TCL_OK;
}
critcl::ccommand zstd::decompress {cdata interp objc objv} {
void *source_buf;
void *dest_buf;
int source_len;
unsigned long long dest_size;
size_t decompressed_size;
if (objc != 2) {
Tcl_WrongNumArgs(interp, 1, objv, "data");
return TCL_ERROR;
}
source_buf = (void *)Tcl_GetByteArrayFromObj(objv[1], &source_len);
dest_size = ZSTD_getDecompressedSize(source_buf, source_len);
if (dest_size == 0) {
Tcl_SetObjResult(interp, Tcl_NewStringObj("invalid data", -1));
return TCL_ERROR;
}
dest_buf = malloc(dest_size);
if (dest_buf == NULL) {
Tcl_SetObjResult(interp,
Tcl_NewStringObj("can't allocate memory to decompress "
"data", -1));
return TCL_ERROR;
}
decompressed_size = ZSTD_decompress(dest_buf, dest_size, source_buf,
source_len);
if (decompressed_size != dest_size) {
Tcl_SetObjResult(interp,
Tcl_ObjPrintf("zstd decoding error: %s",
ZSTD_getErrorName(decompressed_size)));
return TCL_ERROR;
}
Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(dest_buf, decompressed_size));
free(dest_buf);
return TCL_OK;
}
proc zstd::test {} {
critcl::load
puts "zstd version $zstd::version"
puts [zstd::decompress [zstd::compress hello!]]
set ch [open [info script] rb]
set x [read $ch]
close $ch
if {[catch {package require md5}]} {
puts {no package "md5" found -- skipping test}
} else {
set checksum1 [md5::md5 -hex $x]
set y [zstd::compress $x]
set checksum2 [md5::md5 -hex [zstd::decompress $y]]
if {$checksum1 ne $checksum2} {
error {decompressed data differs from original}
}
}
set z [string repeat $x 10000]
puts [string length $z]
zstd::compress $z
foreach level {1 2 3 5 10 19} {
puts [format {level=%1$2d size=%3$d %2$s} \
$level \
[time {
set size [string length [zstd::compress $z $level]]
} 10] \
$size]
}
}
# If this is the main script...
if {[info exists argv0] && ([file tail [info script]] eq [file tail $argv0])} {
zstd::test
}
Sample output
zstd version 1.3.0
hello!
49800000
level= 1 size=6276 20045.6 microseconds per iteration
level= 2 size=6250 19553.2 microseconds per iteration
level= 3 size=6192 19328.7 microseconds per iteration
level= 5 size=6125 19759.4 microseconds per iteration
level=10 size=6103 27139.0 microseconds per iteration
level=19 size=5684 65975.9 microseconds per iteration
See also edit