Mathematically precise calculations can be thrown severely askew by small round-off errors caused by finite-precision floating-point Numbers.
由有限精度浮点数字引起的很小的舍入错误就会严重歪曲数学精度计算。
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However, for negative values of x, roughly -4 and lower, the algorithm used to calculate Math.exp is relatively ill-behaved and subject to round-off error.