问题
I encountered a weird behaviour in Perl. The following subtraction should yield zero as result (which it does in Python):
print 7.6178E-01 - 0.76178
-1.11022302462516e-16
Why does it occur and how to avoid it?
P.S. Effect appears on "v5.10.0 built for x86_64-linux-gnu-thread-multi" (Ubuntu 9.04) and "v5.8.9 built for darwin-2level" (Mac OS 10.6)
回答1:
It's not that scientific notation affects the precision so much as the limitations of floating point notation represented in binary. See the answers to the perlfaq4. This is a problem for any language that relies on the underlying architecture for number storage.
- Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
- Why is int() broken?
If you need better number handling, check out the bignum pragma.
来源：https://stackoverflow.com/questions/2056681/does-scientific-notation-affect-perls-precision