问题
Doing some tests with bitwise operations / shifting with JavaScript
0x80000000 >> 1 // returns -1073741824 (-0x40000000)
I would expect that to return 0x40000000 since
0x40000000 >> 1 // returns 0x20000000
0x20000000 >> 1 // returns 0x10000000
回答1:
Its an arithmetic shift that's why the sign is preserved, to do a logical shift use >>>
0x80000000 >>> 1 // returns 1073741824 (0x40000000)
回答2:
In Javascript, >> is the Signed Right Shift Operator. In §11.7.2 of the language specification it says:
Performs a sign-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
Before the shifting is done, the left operand is converted to a signed 32-bit integer (step 5 of the algorithm given in the specification). In your case this conversion turns the given positive number into a negative value. After that, the actual shifting is done, preserving the negative sign of the value.
来源：https://stackoverflow.com/questions/14061999/why-does-0x80000000-1-in-javascript-produce-a-negative-value