PHP bit operators_PHP tutorial

This involves the bottom layer of the system and is almost never used in WEB development. It would be nice to know that this thing exists. The explanation of the underlying things is always difficult.
Variables stored in memory are binary numbers. Integers occupy 4 bytes on a 32-bit system, and one byte is 8 bits, which is 32 bits. Bit operations are bit-level operations.


$a Hypothetical variables The value of $a is 3, and the value of $b is 2.
Then the format of $a stored in memory is:
00000000 00000000 00000000 00000011
Each time a left shift is performed, all bits are moved to the left, zeros are padded on the right, and excess bits on the left are discarded.
So $a shifts left 2 and gets:
00000000 00000000 00000000 00011000
That is 12. Equivalent to 3 × 2 × 2 =12.

$a >> $b Shift right Moves the bits in $a to the right $b times (each move represents "divide by 2").
Suppose the variable $a has a value of 24 and $b has a value of 2.
Then the format of $a stored in memory is:
00000000 00000000 00000000 00011000
Each time a right shift is performed, all bits are moved from left to right, the excess bits on the right are discarded, and the vacated bits on the left are filled with zeros.
So $a shifts right 2 and gets:
00000000 00000000 00000000 00000110
That is 6. Equivalent to 24 ÷ 2 ÷ 2 = 6.

Displacement operation is the underlying operation of the system, and the operation speed is much faster than multiplication and division. When the optimization code is optimized to the extreme, the number can be converted into a common multiple of two, and then the displacement calculation is performed. But there is almost no need in WEB development, and if it goes beyond the bottom layer of the system, the portability of the program will be reduced.

Other bitwise operators are similar. For example:
$a & $b And (bitwise AND) will set the bits in $a and $b that are both 1 to 1.
Suppose the variable $a has a value of 5 and $b has a value of 6.
$a：
00000000 00000000 00000000 00000101
$b：
00000000 00000000 00000000 00000110
$a & $b :
00000000 00000000 00000000 00000101
00000000 00000000 00000000 00000110
───────────────────────────
00000000 00000000 00000000 00000100
Viewed vertically, if the top and bottom are 1 , we get 1 , otherwise it is 0.
So $a & $b = 4.

~ $a Not (bitwise NOT) Sets bits in $a that are 0 to 1, and vice versa.
~$a：
00000000 00000000 00000000 00000101
───────────────────────────
11111111 11111111 11111111 11111010
If $a is a signed integer, the first bit is the sign bit, and 1 represents a negative number, then ~ $a = -2147483642.
If $a is an unsigned integer and the first bit is still a data bit, then ~ $a = 4294967290.

The following will not be introduced in detail:
$a | $b Or (bitwise OR) will set the bit in $a or $b that is 1 to 1.
$a ^ $b Xor (bitwise exclusive OR) will set different bits in $a and $b to 1.

The usually mentioned multi-bit system refers to how many digits are calculated at the same time when the system processes integers. The above examples are all based on 32-bit systems. Because the excess bits during movement will be discarded, if it is 64-bit or 12-bit, the result of the displacement may be different, and the number of bits during calculation must be adjusted.

from:http://blog.sina.com.cn/s/blog_815611fb01017wtj.html

http://www.bkjia.com/PHPjc/735886.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/735886.htmlTechArticleThis involves the bottom layer of the system and is almost never used in WEB development. It would be nice to know that there is such a thing. The explanation of the underlying things is always difficult. Variables stored in memory are all binary...