Compare PHP's compression functions gzencode, gzdeflate and gzcompress

gzencode uses ZLIB_ENCODING_GZIP encoding by default and uses gzip compression format. It actually uses the defalte algorithm to compress data, and then adds file headers and adler32 verification.

gzdeflate uses ZLIB_ENCODING_RAW encoding by default and uses the deflate data compression algorithm. , in fact, LZ77 is used for compression first, and then Huffman coding is used to compress

gzcompress; ZLIB_ENCODING_DEFLATE encoding is used by default, and zlib compression format is used. Deflate is actually used to compress the data, and then zlib header and CRC correction are added. Verification

The comparison of these three functions is essentially a comparison of three compression methods: deflate, zlib, and gzip.

From the perspective of performance: deflate is better than gzip and better than zlib

From the perspective of the default compression rate of text files after compression: deflate is better than zlib and better than gzip

The authors of gzip and zlib among these three algorithms are Jean-Loup Gailly and Mark Adler.

These two algorithms, as well as the graphics format png, use the deflate algorithm.

The deflate algorithm is a lossless data compression algorithm that uses both the LZ77 algorithm and Huffman Coding.

It was originally defined by Phil Katz for the second version of his PKZIP archiving tool and later defined in the RFC 1951 specification.

The implementation process of compression and decompression of the deflate algorithm can be found on the compression library zlib.

PHP’s compression implementation relies on zlib, which is a function library that provides deflate, zlib, and gzip compression methods.

The above three functions we use, if the encoding in the parameters is changed to the same, and the compression rate is set to the same, then the same function is ultimately called, and the effect and performance are the same.

PHP’s zlib implementation exists in the ext/zlib directory as an extension. The compression function is completed through the three functions of deflateInit2() + deflate() + deflateEnd(), and the decompression function is completed through the three functions of inflateInit2() + inflate() + inflateEnd(). Compression is ultimately called through the php_zlib_encode function. In addition to the input string, compression rate, and result output, the different entry function call parameters are their encoding. The fourth parameter of deflateInit2 specifies encoding. PHP defines three constants:

#define PHP_ZLIB_ENCODING_RAW                                                                                                                                                                                  ine PHP_ZLIB_ENCODING_DEFLATE 0x0f // zlib 15

You can directly specify encoding to use other algorithms during the calling process of the three functions:

zlib: ZLIB_ENCODING_DEFLATE gzip: ZLIB_ENCODING_GZIPdeflate: ZLIB_ENCODING_RAW

These three functions are based on three algorithms Simple calling method, better naming display. The three functions can achieve the same effect by specifying the same encoding, and PHP also provides the zlib_encode function as a universal compression function.

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