PHP variable type 1. what is the maximum floating point number ?, Is double the same as float? 2. how do I know that the value has exceeded? 3. when two numeric strings are compared, do they already think they are being compared? ------ Solution ------------------ 1. the range of float and double is determined by the number of digits of the index. Float indexes have eight digits, while double indexes refer to the PHP variable type.
1. what is the maximum floating point number ?, Is double the same as float?
2. how do I know that the value has exceeded?
3. when two strings of numbers are compared with =, do they already think they are being compared?
------ Solution --------------------
1. Scope
The float and double ranges are determined by the number of digits of the index.
The float Index has eight digits, while the double index has 11 digits. the distribution is as follows:
Float:
1bit (symbol bit) 8 bits (index bit) 23 bits (tail bit)
Double:
1bit (symbol bit) 11 bits (index bit) 52 bits (tail bit)
Therefore, the float index range is-127 ~ + 128, while the double index range is-1023 ~ + 1024, and the index bit is divided by complement code.
The negative index determines the smallest non-zero number of absolute values that floating point numbers can express. the positive index determines the maximum number of absolute values that floating point numbers can express, that is, the value range of floating point numbers.
Float range:-2 ^ 128 ~ + 2 ^ 128, that is,-3.40E + 38 ~ + 3.40E + 38; the double value range is-2 ^ 1024 ~ + 2 ^ 1024, that is,-1.79E + 308 ~ + 1.79E + 308.
2. Precision
The precision of float and double is determined by the number of digits of the ending number. Floating point numbers are stored in the memory in scientific notation, and the integer part is always an implicit "1". since it remains unchanged, it cannot affect the accuracy.
Float: 2 ^ 23 = 8388608, a total of seven digits, which means that there can be a maximum of seven valid digits, but it is absolutely guaranteed to be 6 digits, that is, the float precision is 6 ~ 7 valid digits;
Double: 2 ^ 52 = 4503599627370496, a total of 16 digits. Similarly, the precision of double is 15 ~ 16 bits.
------ Solution --------------------
The two pages (including comments) in the manual answer all your questions:
Http://www.php.net/manual/en/language.types.float.php
Http://www.php.net/manual/en/language.operators.comparison.php
