javascript - Java中~~（“双波浪号”）有什么作用？(What does ~~ (“double tilde”) do in Javascript?)

Question

I was checking out an online game physics library today and came across the ~~ operator.(我今天正在检查一个在线游戏物理库，遇到了~~运算符。)

I know a single ~ is a bitwise NOT, would that make ~~ a NOT of a NOT, which would give back the same value, wouldn't it?(我知道单个?是按位NOT，这会使~~变成NOT的NOT，这会返回相同的值，不是吗？)   ask by Shane Tomlinson translate from so

Answer 1

It removes everything after the decimal point because the bitwise operators implicitly convert their operands to signed 32-bit integers.(它删除小数点后的所有内容，因为按位运算符会将其操作数隐式转换为带符号的32位整数。)

This works whether the operands are (floating-point) numbers or strings, and the result is a number.(无论操作数是（浮点）数字还是字符串，这都有效，并且结果是数字。)

In other words, it yields:(换句话说，它产生：)

function(x) {
  if(x < 0) return Math.ceil(x);
  else return Math.floor(x);
}

only if x is between -(2 ³¹ ) and 2 ³¹ - 1. Otherwise, overflow will occur and the number will "wrap around".(仅当x在-（2 ³¹ ）和2 ^31-1之间 。否则，将发生溢出并且数字将“环绕”。)

This may be considered useful to convert a function's string argument to a number, but both because of the possibility of overflow and that it is incorrect for use with non-integers, I would not use it that way except for "code golf" ( ie pointlessly trimming bytes off the source code of your program at the expense of readability and robustness).(将函数的字符串参数转换为数字可能被认为是有用的，但是由于存在溢出的可能性，并且不适合与非整数一起使用，因此我不以这种方式使用它，除了“ code golf”（ 即无意义地从程序源代码中修剪字节，以牺牲可读性和健壮性为代价）。)

I would use +x or Number(x) instead.(我会改用+x或Number(x) 。)

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How this is the NOT of the NOT(NOT是NOT的NOT)

The number -43.2, for example is:(数字-43.2例如：)

-43.2 ₁₀ = 11111111111111111111111111010101 ₂ (-43.2 ₁₀ = 11111111111111111111111111010101 ₂)

as a signed (two's complement) 32-bit binary number.(作为有符号（二进制补码）的32位二进制数。)

(JavaScript ignores what is after the decimal point.) Inverting the bits gives:(（JavaScript忽略小数点后的内容。）将这些位取反可以得到：)

NOT -43 ₁₀ = 00000000000000000000000000101010 ₂ = 42 ₁₀ (非-43 ₁₀ = 00000000000000000000000000101010 ₂ = 42 ₁₀)

Inverting again gives:(再次反转得到：)

NOT 42 ₁₀ = 11111111111111111111111111010101 ₂ = -43 ₁₀ (不是42 ₁₀ = 11111111111111111111111111010101 ₂ = -43 ₁₀)

This differs from Math.floor(-43.2) in that negative numbers are rounded toward zero, not away from it.(这与Math.floor(-43.2)不同之处在于负数四舍五入为零，而不是四舍五入。)

(The floor function, which would equal -44, always rounds down to the next lower integer, regardless of whether the number is positive or negative.)(（等于-44的下限函数始终舍入为下一个较小的整数，而不管该数是正数还是负数。）)