为什么 Java BigInteger 说 'probably prime' 而不是 'certainly prime'？
Why does Java BigInteger say 'probably prime' and not 'certainly prime'?
BigInteger的JavaDoc让我很没有安全感，例如下面的构造函数说：
BigInteger(int bitLength, int certainty, Random rnd)
Constructs a randomly generated positive BigInteger that is probably
prime, with the specified bitLength.
为什么只有大概？为什么不肯定？我还能相信结果会是质数吗？
来自 docs 的 BigInteger(int bitLength, int certainty, Random rnd):
certainty: a measure of the uncertainty that the caller is
willing to tolerate. The probability that the new BigInteger
represents a prime number will exceed
(1 - ½certainty). The execution time of
this constructor is proportional to the value of this parameter.
所以构造函数让你确定它将是质数，这就是为什么文档说 "probably"
因为概率算法的运行速度比验证数字绝对是素数要快得多。
BigInteger的JavaDoc让我很没有安全感，例如下面的构造函数说：
BigInteger(int bitLength, int certainty, Random rnd)
Constructs a randomly generated positive BigInteger that is probably prime, with the specified bitLength.
为什么只有大概？为什么不肯定？我还能相信结果会是质数吗？
来自 docs 的 BigInteger(int bitLength, int certainty, Random rnd):
certainty: a measure of the uncertainty that the caller is willing to tolerate. The probability that the new BigInteger represents a prime number will exceed (1 - ½certainty). The execution time of this constructor is proportional to the value of this parameter.
所以构造函数让你确定它将是质数，这就是为什么文档说 "probably"
因为概率算法的运行速度比验证数字绝对是素数要快得多。