javascript - rounding down in js

Question

In js, in the past, the Math.floor method was used to round down, but now we see this usage: OR operation
interval = interval | 0
Why can we round down in this way? , what are the advantages of this usage compared with Math.floor?

Answer 1

Note that | is not a logical OR, but a bitwise OR (OR).

Some small differences. For example, Math.floor(NaN) still returns NaN. But NaN | 0 returns 0.
Another example is Math.floor(Infinity) returns Infinity, but Infinity | 0 returns 0

Answer 2

You can also do this interval = interval >> 0

Answer 3

• First of all, S1ngS1ng upstairs is right about those small differences.

• In addition, | is a bitwise OR operation. Since when 0 is stored in the memory, all integer bits are filled with 0, so the OR operation is performed based on the binary bit and a numerical value. Regardless of the corresponding bit Whether 0 or 1 is ORed with 0, you will get itself. However, since the number 0 does not have a decimal part in the memory, the decimal part of interval is discarded after the bitwise OR operation. In fact, rounding down is achieved by discarding the decimal part.

• Since it is a bit operation, it will be faster than Math.floor().

Answer 4

The real reason is: automatic type conversion within js.

js values ​​are all expressed in 64-bit floating point type. When a value requires bit operations, js will automatically convert it into a 32-bit signedinteger and discard the decimal part.

n|0; n>>0; //The following 0 is only used to ensure that the integer value of n remains unchanged.

Reducing from 64-bit to 32-bit will cause a loss of accuracy. Be careful! , maximum effective range: 2^32/2-1

> f64=(Math.pow( 2,32)/2-1)-0.5
2147483646.5
> f64|0
2147483646
> f64>>0
2147483646
> (f64 + 2)|0 //超出有效范围
-2147483648
> (f64 + 2)>>0 //超出有效范围
-2147483648
> Math.floor(f64 + 2) //正确
2147483648

Answer 5

Both can be achieved, interval = interval | 0 This is a writing technique, it depends on personal preference. It may be that interval = interval | 0 will run faster, and writing code will definitely be faster than Math.floor!