From 71a1e55230963b0ebccdfce56c8e2e88437e239a Mon Sep 17 00:00:00 2001
From: Markus Kohlhase <markus.kohlhase@slowtec.de>
Date: Tue, 19 Mar 2024 02:33:15 +0100
Subject: [PATCH] Mark some functions as const

---
 src/codec/mod.rs     | 23 +++++++++++------------
 src/codec/rtu/mod.rs |  2 +-
 src/codec/tcp/mod.rs |  2 +-
 src/frame/coils.rs   | 11 ++++++++---
 src/lib.rs           |  1 +
 5 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/src/codec/mod.rs b/src/codec/mod.rs
index 4bc394d..f63a3e9 100644
--- a/src/codec/mod.rs
+++ b/src/codec/mod.rs
@@ -277,7 +277,6 @@ impl<'r> Encode for Request<'r> {
 
 impl<'r> Encode for Response<'r> {
     fn encode(&self, buf: &mut [u8]) -> Result<usize> {
-        use crate::frame::Response as R;
 
         if buf.len() < self.pdu_len() {
             return Err(Error::BufferSize);
@@ -285,26 +284,26 @@ impl<'r> Encode for Response<'r> {
 
         buf[0] = FnCode::from(*self).into();
         match self {
-            R::ReadCoils(coils) | R::ReadDiscreteInputs(coils) => {
+            Self::ReadCoils(coils) | Self::ReadDiscreteInputs(coils) => {
                 buf[1] = coils.packed_len() as u8;
                 coils.copy_to(&mut buf[2..]);
             }
-            R::ReadInputRegisters(registers)
-            | R::ReadHoldingRegisters(registers)
-            | R::ReadWriteMultipleRegisters(registers) => {
+            Self::ReadInputRegisters(registers)
+            | Self::ReadHoldingRegisters(registers)
+            | Self::ReadWriteMultipleRegisters(registers) => {
                 buf[1] = (registers.len() * 2) as u8;
                 registers.copy_to(&mut buf[2..]);
             }
-            R::WriteSingleCoil(address) => {
+            Self::WriteSingleCoil(address) => {
                 BigEndian::write_u16(&mut buf[1..], *address);
             }
-            R::WriteMultipleCoils(address, payload)
-            | R::WriteMultipleRegisters(address, payload)
-            | R::WriteSingleRegister(address, payload) => {
+            Self::WriteMultipleCoils(address, payload)
+            | Self::WriteMultipleRegisters(address, payload)
+            | Self::WriteSingleRegister(address, payload) => {
                 BigEndian::write_u16(&mut buf[1..], *address);
                 BigEndian::write_u16(&mut buf[3..], *payload);
             }
-            R::Custom(_, custom_data) => {
+            Self::Custom(_, custom_data) => {
                 for (idx, d) in custom_data.iter().enumerate() {
                     buf[idx + 1] = *d;
                 }
@@ -343,7 +342,7 @@ impl Encode for ExceptionResponse {
     }
 }
 
-fn min_request_pdu_len(fn_code: FnCode) -> usize {
+const fn min_request_pdu_len(fn_code: FnCode) -> usize {
     use FnCode as F;
     match fn_code {
         F::ReadCoils
@@ -358,7 +357,7 @@ fn min_request_pdu_len(fn_code: FnCode) -> usize {
     }
 }
 
-fn min_response_pdu_len(fn_code: FnCode) -> usize {
+const fn min_response_pdu_len(fn_code: FnCode) -> usize {
     use FnCode as F;
     match fn_code {
         F::ReadCoils
diff --git a/src/codec/rtu/mod.rs b/src/codec/rtu/mod.rs
index 9d41321..ae2e980 100644
--- a/src/codec/rtu/mod.rs
+++ b/src/codec/rtu/mod.rs
@@ -133,7 +133,7 @@ pub fn crc16(data: &[u8]) -> u16 {
 }
 
 /// Extract the PDU length out of the ADU request buffer.
-pub fn request_pdu_len(adu_buf: &[u8]) -> Result<Option<usize>> {
+pub const fn request_pdu_len(adu_buf: &[u8]) -> Result<Option<usize>> {
     if adu_buf.len() < 2 {
         return Ok(None);
     }
diff --git a/src/codec/tcp/mod.rs b/src/codec/tcp/mod.rs
index b02a51d..e2fd60c 100644
--- a/src/codec/tcp/mod.rs
+++ b/src/codec/tcp/mod.rs
@@ -118,7 +118,7 @@ pub fn extract_frame(buf: &[u8], pdu_len: usize) -> Result<Option<DecodedFrame>>
 }
 
 /// Extract the PDU length out of the ADU request buffer.
-pub fn request_pdu_len(adu_buf: &[u8]) -> Result<Option<usize>> {
+pub const fn request_pdu_len(adu_buf: &[u8]) -> Result<Option<usize>> {
     if adu_buf.len() < 8 {
         return Ok(None);
     }
diff --git a/src/frame/coils.rs b/src/frame/coils.rs
index b6a009d..6031de7 100644
--- a/src/frame/coils.rs
+++ b/src/frame/coils.rs
@@ -17,6 +17,7 @@ impl<'c> Coils<'c> {
             quantity: bools.len(),
         })
     }
+
     //TODO: add tests
     pub(crate) fn copy_to(&self, buf: &mut [u8]) {
         let packed_len = self.packed_len();
@@ -25,24 +26,28 @@ impl<'c> Coils<'c> {
             buf[idx] = self.data[idx];
         });
     }
+
     /// Quantity of coils
     #[must_use]
     pub const fn len(&self) -> usize {
         self.quantity
     }
+
     /// Number of bytes required to pack the coils.
     #[must_use]
     pub const fn packed_len(&self) -> usize {
         packed_coils_len(self.quantity)
     }
+
     ///  Returns `true` if the container has no items.
     #[must_use]
     pub const fn is_empty(&self) -> bool {
         self.quantity == 0
     }
+
     /// Get a specific coil.
     #[must_use]
-    pub fn get(&self, idx: usize) -> Option<Coil> {
+    pub const fn get(&self, idx: usize) -> Option<Coil> {
         if idx + 1 > self.quantity {
             return None;
         }
@@ -82,7 +87,7 @@ impl<'c> IntoIterator for Coils<'c> {
 
 /// Turn a bool into a u16 coil value
 #[must_use]
-pub fn bool_to_u16_coil(state: bool) -> u16 {
+pub const fn bool_to_u16_coil(state: bool) -> u16 {
     if state {
         0xFF00
     } else {
@@ -91,7 +96,7 @@ pub fn bool_to_u16_coil(state: bool) -> u16 {
 }
 
 /// Turn a u16 coil value into a boolean value.
-pub fn u16_coil_to_bool(coil: u16) -> Result<bool, Error> {
+pub const fn u16_coil_to_bool(coil: u16) -> Result<bool, Error> {
     match coil {
         0xFF00 => Ok(true),
         0x0000 => Ok(false),
diff --git a/src/lib.rs b/src/lib.rs
index 9dda669..ead8618 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,7 @@
 #![warn(unsafe_code)]
 #![warn(unused)]
 // Clippy lints
+#![warn(clippy::missing_const_for_fn)]
 #![warn(clippy::pedantic)]
 #![allow(clippy::cast_possible_truncation)] // FIXME
 #![allow(clippy::missing_errors_doc)]