问题
I've got a really big number: 5799218898. And want to shift it right to 13 bits.
So, windows-calculator or python gives me:
5799218898 >> 13 | 100010100100001110011111100001 >> 13 70791 | 10001010010000111
As expected.
But Javascript:
5799218898 >> 13 | 100010100100001110011111100001 >> 13 183624 | 101100110101001000
I think it because of internal integer representation in javascript, but cannot find anything about that.
回答1:
In ECMAScript (Javascript) bitwise operations are always in 32-bit. Therefore 5799218898 is chopped into 32-bit which becomes 1504251602. This integer >> 13 gives 183624.
In Python they are arbitrary-length integers. So there's no problem.
(And the numbers in Windows calculator are 64-bit, enough to fit 5799218898.)
(And the correct answer should be 707912.)
回答2:
The number you have (5799218898) is beyond 32 bits. You didn't mention the JavaScript engine you're testing with, but it's very likely that it is 32-bit.
To test, trim the "5" at the beginning of your number so that you fall inside the 32-bit boundary. Then your shift should work fine.
回答3:
As Nicholas Zakas states:
Even though JavaScript numbers are technically stored in 64-bits, integer values are treated as if they’re 32 bits whenever bitwise operators are involved.
来源：https://stackoverflow.com/questions/2373791/bitshift-in-javascript