How do I round a double to 0.00005?

Asked Feb 11 '20 at 13:58

Active Feb 11 '20 at 14:03

Viewed 59 times

I have a double and I want to round down to values 0.00000/0.00005 using C89/ANSI C. So:

1.10984 becomes 1.10980
1.10985 becomes 1.10985
1.10986 becomes 1.10985
1.10988 becomes 1.10985
1.10989 becomes 1.10985
1.10990 becomes 1.10990
1.10991 becomes 1.10990

I have tried:

roundedDouble = doubleToRound - (doubleToRound % 0.00005);

But % operator only works with integers.

Solution shall work also with the following rounding down cases:

0.000000 / 0.000025 / 0.000050 / 0.000075

and

0.00001 / 0.00002 / 0.00003 / 0.00004 / ... / 0.00008 / 0.00009

edited Feb 11 '20 at 14:03

asked Feb 11 '20 at 13:58

M.E.

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[`fmod()`](https://en.cppreference.com/w/c/numeric/math/fmod) works with `double`. – 001 Feb 11 '20 at 14:03
2

The solution will certainly be approximate as typical `double` cannot represent `0.00005` _exactly_. – chux - Reinstate Monica Feb 11 '20 at 14:05
I will try fmod() and see what happens with the representation inaccuracy of double. – M.E. Feb 11 '20 at 14:07

How do I round a double to 0.00005?

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