BigInt.asIntN()

¥Syntax

BigInt.asIntN(bits, bigint)

¥Parameters

bits

返回的 BigInt 可用的位数。应为 0 到 2 之间的整数⁵³ - 1、包容性。

bigint

要截断以适合提供的位的 BigInt 值。

¥Return value

bigint 模 2^bits 的值，作为有符号整数。

¥The value of bigint modulo 2^bits, as a signed integer.

¥Exceptions

RangeError

如果 bits 为负数或大于 2⁵³，则抛出该异常 - 1.

¥Description

BigInt.asIntN 方法将 BigInt 值截断为给定的位数，并将结果解释为有符号整数。例如，对于 BigInt.asIntN(3, 25n)，值 25n 被截断为 1n：

¥The BigInt.asIntN method truncates a BigInt value to the given number of bits, and interprets the result as a signed integer. For example, for BigInt.asIntN(3, 25n), the value 25n is truncated to 1n:

25n = 00011001 (base 2)
          ^=== Use only the three remaining bits
===>       001 (base 2) = 1n

如果剩余数的首位是 1，则结果为负数。例如，BigInt.asIntN(4, 25n) 产生 -7n，因为 1001 是 -7 在二进制补码下的编码：

¥If the leading bit of the remaining number is 1, the result is negative. For example, BigInt.asIntN(4, 25n) yields -7n, because 1001 is the encoding of -7 under two's complement:

25n = 00011001 (base 2)
         ^==== Use only the four remaining bits
===>      1001 (base 2) = -7n

注意：BigInt 值始终编码为二进制补码。

¥Note: BigInt values are always encoded as two's complement in binary.

与 Number.prototype.toExponential() 等类似语言 API 不同，asIntN 是 BigInt 的静态属性，因此你始终将其用作 BigInt.asIntN()，而不是用作 BigInt 值的方法。将 asIntN() 暴露为 "标准库函数" 允许 与 asm.js 互操作。

¥Unlike similar language APIs such as Number.prototype.toExponential(), asIntN is a static property of BigInt, so you always use it as BigInt.asIntN(), rather than as a method of a BigInt value. Exposing asIntN() as a "standard library function" allows interop with asm.js.

¥Examples

¥Staying in 64-bit ranges

BigInt.asIntN() 方法对于保持在 64 位算术范围内非常有用。

¥The BigInt.asIntN() method can be useful to stay in the range of 64-bit arithmetic.

const max = 2n ** (64n - 1n) - 1n;

BigInt.asIntN(64, max); // 9223372036854775807n

BigInt.asIntN(64, max + 1n); // -9223372036854775808n
// negative because the 64th bit of 2^63 is 1

¥See also

• BigInt
• BigInt.asUintN()