Google Calc floating point error: 16384.69-16384.58=0.10999999999 | Hacker News Reader

Google Calc floating point error: 16384.69-16384.58=0.10999999999

google.com

The Google Calculator returns incorrect results for the range:

  16384.69 - 16384.58 (0.10999999999)
  16385.69 - 16385.58 (0.10999999999)
  ...
  32766.69 - 32766.58 (0.10999999999)
  32767.69 - 32767.58 (0.10999999999)

Results are correct on either side of this range:

  16383.69 - 16383.58 (0.11)
  32768.69 - 32768.58 (0.11)

You say "incorrect", I say "incompatible assumptions". http://blog.reverberate.org/2014/09/what-every-computer-prog...

(TL;DR: Floating point arithmetic on binary numbers doesn't translate into decimal numbers intuitively, "weird" rounding errors appear.)

What is interesting is that, given its massive scale, Google is not performing decimal arithmetic for users. It's not that I don't understand why it isn't, but I think it highlights Google's values in regard to meeting the needs of ordinary people: e.g. how is a school teacher supposed to explain this to third graders?

Good question. I'm in no way connected to Google, but I'm guessing this calculator could be a toy held together by string and duct tape, without any deeper thought having gone into its handling of numbers - floats being the default for non-integer numbers, it's likely that they were used; decimals require more coding and attention.

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