## fsum

The library to calculate accurate sum of floats

### 3 releases

 0.1.2 Feb 25, 2022 Feb 22, 2022 Feb 21, 2022

#1626 in Algorithms

Used in 5 crates (2 directly)

MIT/Apache

11KB
132 lines

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

# Example

``````use fsum::FSum;

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) `sum` method of `test::stats::Stats` implementation for `f64` (which probably reimplements `math.fsum` from Python's library) and source of CPython. See also:

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