From 68aac98753dba77bccc6572c65d441108dc53a17 Mon Sep 17 00:00:00 2001
From: "Jamil Lambert, PhD" <Jamil.Lambert@proton.me>
Date: Fri, 15 Nov 2024 09:02:15 +0000
Subject: [PATCH] Mark functions `const`

Mark `checked_` functions const.
Replace `map()` and `?` operators, which are not allowed in const
context, with match statements.
---
 units/src/fee_rate.rs | 44 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/units/src/fee_rate.rs b/units/src/fee_rate.rs
index 282c246640..4ed19f685b 100644
--- a/units/src/fee_rate.rs
+++ b/units/src/fee_rate.rs
@@ -79,12 +79,24 @@ impl FeeRate {
     /// Checked multiplication.
     ///
     /// Computes `self * rhs` returning [`None`] if overflow occurred.
-    pub fn checked_mul(self, rhs: u64) -> Option<Self> { self.0.checked_mul(rhs).map(Self) }
+    pub const fn checked_mul(self, rhs: u64) -> Option<Self> {
+        // No `map()` in const context.
+        match self.0.checked_mul(rhs) {
+            Some(res) => Some(Self(res)),
+            None => None,
+        }
+    }
 
     /// Checked division.
     ///
     /// Computes `self / rhs` returning [`None`] if `rhs == 0`.
-    pub fn checked_div(self, rhs: u64) -> Option<Self> { self.0.checked_div(rhs).map(Self) }
+    pub const fn checked_div(self, rhs: u64) -> Option<Self> {
+        // No `map()` in const context.
+        match self.0.checked_div(rhs) {
+            Some(res) => Some(Self(res)),
+            None => None,
+        }
+    }
 
     /// Checked weight multiplication.
     ///
@@ -94,20 +106,38 @@ impl FeeRate {
     /// rounded down.
     ///
     /// [`None`] is returned if an overflow occurred.
-    pub fn checked_mul_by_weight(self, rhs: Weight) -> Option<Amount> {
-        let sats = self.0.checked_mul(rhs.to_wu())?.checked_add(999)? / 1000;
-        Some(Amount::from_sat(sats))
+    pub const fn checked_mul_by_weight(self, rhs: Weight) -> Option<Amount> {
+        // No `?` operator in const context.
+        match self.0.checked_mul(rhs.to_wu()) {
+            Some(mul_res) => match mul_res.checked_add(999) {
+                Some(add_res) => Some(Amount::from_sat(add_res / 1000)),
+                None => None,
+            },
+            None => None,
+        }
     }
 
     /// Checked addition.
     ///
     /// Computes `self + rhs` returning [`None`] if overflow occured.
-    pub fn checked_add(self, rhs: u64) -> Option<Self> { self.0.checked_add(rhs).map(Self) }
+    pub const fn checked_add(self, rhs: u64) -> Option<Self> {
+        // No `map()` in const context.
+        match self.0.checked_add(rhs) {
+            Some(res) => Some(Self(res)),
+            None => None,
+        }
+    }
 
     /// Checked subtraction.
     ///
     /// Computes `self - rhs` returning [`None`] if overflow occured.
-    pub fn checked_sub(self, rhs: u64) -> Option<Self> { self.0.checked_sub(rhs).map(Self) }
+    pub const fn checked_sub(self, rhs: u64) -> Option<Self> {
+        // No `map()` in const context.
+        match self.0.checked_sub(rhs) {
+            Some(res) => Some(Self(res)),
+            None => None,
+        }
+    }
 
     /// Calculates the fee by multiplying this fee rate by weight, in weight units, returning [`None`]
     /// if an overflow occurred.