[#FeePerUnit]
= FeePerUnit
:mrdocs:

Tagged wrapper around FeeFrac to avoid unit confusion.

== Synopsis

Declared in `<util/feefrac.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename Tag>
struct FeePerUnit
    : xref:FeeFrac.adoc[FeeFrac]
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:FeeFrac.adoc[FeeFrac]`
| Data structure storing a fee and size.
|===

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:FeeFrac/operator_assign.adoc[`operator=`] 
| Copy‐assign the fee and size from another FeeFrac.
| xref:FeeFrac/EvaluateFee.adoc[`EvaluateFee`] 
| Compute the fee for a given size `at_size` using this object's feerate.
| xref:FeeFrac/EvaluateFeeDown.adoc[`EvaluateFeeDown`] 
| Compute the fee for a given size `at_size` using this object's feerate, rounding down.
| xref:FeeFrac/EvaluateFeeUp.adoc[`EvaluateFeeUp`] 
| Compute the fee for a given size `at_size` using this object's feerate, rounding up.
| xref:FeeFrac/IsEmpty.adoc[`IsEmpty`] 
| Check if this is empty (size and fee are 0).
| xref:FeeFrac/operator_plus_eq.adoc[`operator+=`] 
| Add fee and size of another FeeFrac to this one.
| xref:FeeFrac/operator_minus_eq.adoc[`operator‐=`] 
| Subtract fee and size of another FeeFrac from this one.
|===


== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:FeeFrac/Div.adoc[`Div`] 
| Helper function for 96/32 signed division, rounding towards negative infinity (if round_down), or towards positive infinity (if !round_down). This is a version relying on __int128.
| xref:FeeFrac/DivFallback.adoc[`DivFallback`] 
| Helper function for 96/32 signed division, rounding towards negative infinity (if round_down) or positive infinity (if !round_down). This is a fallback version, separate so that it can be tested on platforms where it isn't actually needed.
| xref:FeePerUnit/FromFeeFrac.adoc[`FromFeeFrac`] 
| Convert a FeeFrac to a FeePerUnit.
| xref:FeeFrac/Mul.adoc[`Mul`] 
| Helper function for 32*64 signed multiplication, returning an unspecified but totally ordered type. This is a version relying on __int128.
| xref:FeeFrac/MulFallback.adoc[`MulFallback`] 
| Helper function for 32*64 signed multiplication, returning an unspecified but totally ordered type. This is a fallback version, separate so it can be tested on platforms where it isn't actually needed.
|===


== Data Members

[cols="1,4"]
|===
| Name| Description
| xref:FeeFrac/fee.adoc[`fee`] 
| The fee, in satoshis.
| xref:FeeFrac/size.adoc[`size`] 
| The size, in the unit chosen by the caller (for example vbytes or weight units).
|===


== Using Declarations

[cols="1,4"]
|===
| Name| Description
| xref:FeePerUnit/2constructor.adoc[`FeePerUnit`] 
| Inherit the FeeFrac constructors.
|===


== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:operator_plus-0f3.adoc[`operator+`]
| Sum fee and size.
| xref:operator_minus-0b.adoc[`operator‐`]
| Subtract both fee and size.
| xref:operator_eq-03b.adoc[`operator==`]
| Check if two FeeFrac objects are equal (both same fee and same size).
| xref:swap-02.adoc[`swap`]
| Swap two FeeFracs.
|===


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