快速找到2 ^ x的方法(Method to find 2^x quickly)

快速找到2 ^ x的方法(Method to find 2^x quickly)

如何在C中快速找到2 ^ x。如果你们有任何想法，请帮忙。

How to find 2^x quickly in C. If you guys have any idea please help.

最满意答案

向左移位时，对于每个位置移位，这将数字乘以2，与将左移十进制数字乘以10相同。

使用<<运算符，如下所示：

int twoPowZero = 1; // any number^0 is 1 int twoPowOne = 1 << 1; // this sets the '2' bit to '1' int twoPowTwo = 1 << 2; int twoPowFive = 1 << 5; int twoPowTen = 1 << 10;

依此类推，直到你达到1 << 30 。 如果你使用一个有符号的32位整数，那么1 << 31会给你-2147483648，因为有二进制补码。 如果你想要比使用long long unsigned int或uint64_t （64位整数）更高。 或者，如果您的平台支持它： uint128_t 。

如果你想要更高，你需要推出自己的“大整数”代码。 请注意，某些平台和编译器带有128位整数类型，但运行时性能各不相同：它们可能需要可执行128位操作的处理器，或者可能会将其分解为两个64位操作。

Bitshift to the left, this multiplies numbers by 2 for every place shift, in the same way that shifting decimal numbers to the left multiplies them by 10.

Use the << operator, like so:

int twoPowZero = 1; // any number^0 is 1 int twoPowOne = 1 << 1; // this sets the '2' bit to '1' int twoPowTwo = 1 << 2; int twoPowFive = 1 << 5; int twoPowTen = 1 << 10;

and so on until you get to 1 << 30. If you're using a signed 32-bit integer then 1 << 31 will give you -2147483648 because of two's complement. If you want to go higher than use long long unsigned int or uint64_t (64-bit integer). Or if your platform supports it: uint128_t.

If you want to go even higher, you'll need to roll your own "big integer" code. Note that some platforms and compilers come with a 128-bit integer type, but runtime performance varies: they may require a processor that can perform 128-bit operations, or they might break it down into two 64-bit operations.