### 3 releases

0.1.2 | Feb 25, 2022 |
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0.1.1 | Feb 22, 2022 |

0.1.0 | Feb 21, 2022 |

#**1626** in Algorithms

**150** downloads per month

Used in **5** crates
(2 directly)

**MIT/Apache**

11KB

132 lines

is the Rust library by Piotr Beling to calculate accurate sum of floats.`fsum`

# Example

`use` `fsum``::`FSum`;`
`assert_eq!``(``FSum``::`new`(``)``.``add``(`1e100`)``.``add``(``1.``0``)``.``add``(``-`1e100`)``.``value``(``)``,` `1.``0``)``;`
`assert_eq!``(``FSum``::`with_all`(``(``0``..``10``)``.``map``(``|``_``|` `0.``1``)``)``.``value``(``)``,` `1.``0``)``;`
`assert_eq!``(``FSum``::`with_all`(``&``[`1e100`,` `1.``0``,` `-`1e100`]``)``.``value``(``)``,` `1.``0``)``;`
`let` `mut` s `=` `FSum``::`new`(``)``;`
`assert_eq!``(`s`.``value``(``)``,` `0.``0``)``;`
s `+=` `3.``0``;`
`assert_eq!``(`s`.``value``(``)``,` `3.``0``)``;`
s `-=` `1.``0``;`
`assert_eq!``(`s`.``value``(``)``,` `2.``0``)``;`

# Complexity

The complexities of summing *n* numbers are:

- time: from
*O(n)*(optimistic) to*O(n²)*(pessimistic) - memory: from
*O(1)*(optimistic) to*O(n)*(pessimistic)

Usually the complexities are close to optimistic.

# References

Calculation code bases on (is mostly copied from)

method
of `sum`

implementation for `test ::`

`stats`Stats

`::``f64`

(which probably reimplements `math``.`fsum

from Python's library)
and source of CPython.
See also:- https://github.com/python/cpython/blob/2b7411df5ca0b6ef714377730fd4d94693f26abd/Lib/test/test_math.py#L647
- https://bugs.python.org/file10357/msum4.py
- http://code.activestate.com/recipes/393090/

The method sacrifices performance at the altar of accuracy Depends on IEEE-754 arithmetic guarantees. See proof of the correctness in Adaptive Precision Floating-Point Arithmetic and Fast Robust Geometric Predicates