


PHP compression function implementation: the difference between gzencode, gzdeflate and gzcompress, gzencodegzdeflate
•gzencode uses ZLIB_ENCODING_GZIP encoding by default, uses gzip compression format, and actually uses the defalte algorithm to compress data , then add the file header and adler32 check
•gzdeflate uses the ZLIB_ENCODING_RAW encoding method by default and uses the deflate data compression algorithm. In fact, it is first compressed with LZ77 and then compressed with Huffman coding
•gzcompress; ZLIB_ENCODING_DEFLATE encoding is used by default, using zlib compression format. It actually uses deflate to compress the data, and then adds zlib header and CRC check
The comparison of these three functions is essentially a comparison of three compression methods: deflate, zlib, and gzip.
From a performance perspective: deflate is better than gzip and zlib
Judging from the dimension of the text file’s default compression rate after compression: deflate is better than zlib and is 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 version 2 of his PKZIP archiving tool and later 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 used, if the encoding in the parameters is converted to the same value and the compression rate is set to the same value, the same function will be called in the end, and the effect and performance will be the same.
PHP’s zlib implementation exists in the ext/zlib directory as an extension. The three functions of deflateInit2() deflate() deflateEnd() cooperate to complete the compression function, and the three functions of inflateInit2() inflate() inflateEnd() cooperate to complete the decompression function. 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:
Copy code The code is as follows:
#define PHP_ZLIB_ENCODING_RAW -0xf //deflate -15
#define PHP_ZLIB_ENCODING_GZIP 0x1f
#define PHP_ZLIB_ENCODING_DEFLATE 0x0f // zlib 15
You can directly specify encoding to use other algorithms during the calling process of the three functions:
Copy code The code is as follows:
zlib: ZLIB_ENCODING_DEFLATE
gzip: ZLIB_ENCODING_GZIP
deflate: ZLIB_ENCODING_RAW
Reference:
http://shouce.jb51.net/gzip/rfc-deflate.html
http://www.gzip.org/zlib/rfc-deflate.html
- Detailed examples of php ZipArchive compression function

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。


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