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Update readme to add a comparison section #630

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Expand Up @@ -346,3 +346,25 @@ which was released on `2022-04-07`.
This library maintains support for rust compiler versions that are 4 minor versions away from the current stable rust compiler version.
For example, if the current stable compiler version is `1.50.0` then we will guarantee support up to and including `1.46.0`.
Of note, we will only update the minimum supported version if and when required.

## Comparison to other Decimal implementations

During the development of this library, there were various design decisions made to ensure that decimal calculations would
be quick, accurate and efficient. Some decisions, however, put limitations on what this library can do and ultimately what
it is suitable for. One such decision was the structure of the internal decimal representation.

This library uses a mantissa of 96 bits made up of three 32-bit unsigned integers with a fourth 32-bit unsigned integer to represent the scale/sign
(similar to the C and .NET Decimal implementations).
This structure allows us to make use of algorithmic optimizations to implement basic arithmetic; ultimately this gives us the ability
to squeeze out performance and make it one of the fastest implementations available. The downside of this approach however is that
the maximum number of significant digits that can be represented is roughly 28 base-10 digits (29 in some cases).

While this constraint is not an issue for many applications (e.g. when dealing with money), some applications may require a higher number of significant digits to be represented. Fortunately,
there are alternative implementations that may be worth investigating, such as:

* [bigdecimal](https://crates.io/crates/bigdecimal)
* [decimal-rs](https://crates.io/crates/decimal-rs)

If you have further questions about the suitability of this library for your project, then feel free to either start a
[discussion](https://github.com/paupino/rust-decimal/discussions) or open an [issue](https://github.com/paupino/rust-decimal/issues) and we'll
do our best to help.