clarify scalar values a bit more and update comments

contracts/distribution/dao-rewards-distributor/src/helpers.rs

@@ -37,8 +37,8 @@ pub fn get_voting_power_at_block(
 }
 
 /// returns underlying scalar value for a given duration.
-/// if the duration is in blocks, returns the block height.
-/// if the duration is in time, returns the time in seconds.
+/// if the duration is a block height, return the number of blocks.
+/// if the duration is a time, return the number of seconds.
 pub fn get_duration_scalar(duration: &Duration) -> u64 {
     match duration {
         Duration::Height(h) => *h,
@@ -73,9 +73,13 @@ pub(crate) fn scale_factor() -> Uint256 {
     Uint256::from(10u8).pow(39)
 }
 
-/// Calculate the duration from start to end. If the end is at or before the
-/// start, return 0. The first argument is end, and the second is start.
-pub fn get_exp_diff(end: &Expiration, start: &Expiration) -> StdResult<u64> {
+/// Calculate the duration scalar value from start to end. If the end is at or
+/// before the start, return 0. The first argument is end, and the second is
+/// start. If start and end are block heights, this returns the number of
+/// blocks. If they are times, this returns the number of seconds. If both are
+/// never, this returns 0. If start and end have different units, it errors as
+/// that should not be possible.
+pub fn get_exp_diff_scalar(end: &Expiration, start: &Expiration) -> StdResult<u64> {
     match (end, start) {
         (Expiration::AtHeight(end), Expiration::AtHeight(start)) => {
             if end > start {

contracts/distribution/dao-rewards-distributor/src/rewards.rs

@@ -2,8 +2,8 @@ use cosmwasm_std::{Addr, BlockInfo, Deps, DepsMut, Env, StdResult, Uint128, Uint
 
 use crate::{
     helpers::{
-        get_duration_scalar, get_exp_diff, get_prev_block_total_vp, get_voting_power_at_block,
-        scale_factor,
+        get_duration_scalar, get_exp_diff_scalar, get_prev_block_total_vp,
+        get_voting_power_at_block, scale_factor,
     },
     state::{DistributionState, EmissionRate, UserRewardState, DISTRIBUTIONS, USER_REWARDS},
     ContractError,
@@ -98,15 +98,15 @@ pub fn get_active_total_earned_puvp(
             // get the duration from the last time rewards were updated to the
             // last time rewards were distributed. this will be 0 if the rewards
             // were updated at or after the last time rewards were distributed.
-            let new_reward_distribution_duration: Uint128 = get_exp_diff(
+            let new_reward_distribution_duration_scalar: Uint128 = get_exp_diff_scalar(
                 &last_time_rewards_distributed,
                 &distribution.active_epoch.last_updated_total_earned_puvp,
             )?
             .into();
 
             // no need to query total voting power and do math if distribution
             // is already up to date.
-            if new_reward_distribution_duration.is_zero() {
+            if new_reward_distribution_duration_scalar.is_zero() {
                 return Ok(curr);
             }
 
@@ -118,7 +118,7 @@ pub fn get_active_total_earned_puvp(
             } else {
                 // count intervals of the rewards emission that have passed
                 // since the last update which need to be distributed
-                let complete_distribution_periods = new_reward_distribution_duration
+                let complete_distribution_periods = new_reward_distribution_duration_scalar
                     .checked_div(get_duration_scalar(&duration).into())?;
 
                 // It is impossible for this to overflow as total rewards can

contracts/distribution/dao-rewards-distributor/src/state.rs

@@ -9,7 +9,7 @@ use cw_utils::Duration;
 use std::{cmp::min, collections::HashMap};
 
 use crate::{
-    helpers::{get_duration_scalar, get_exp_diff, get_prev_block_total_vp, scale_factor},
+    helpers::{get_duration_scalar, get_exp_diff_scalar, get_prev_block_total_vp, scale_factor},
     rewards::get_active_total_earned_puvp,
     ContractError,
 };
@@ -70,7 +70,7 @@ impl EmissionRate {
             EmissionRate::Linear {
                 amount, duration, ..
             } => {
-                if *amount == Uint128::zero() {
+                if amount.is_zero() {
                     return Err(ContractError::InvalidEmissionRateFieldZero {
                         field: "amount".to_string(),
                     });
@@ -236,16 +236,13 @@ impl DistributionState {
             EmissionRate::Linear {
                 amount, duration, ..
             } => {
-                let epoch_duration =
-                    get_exp_diff(&self.active_epoch.ends_at, &self.active_epoch.started_at)?;
+                let epoch_duration_scalar =
+                    get_exp_diff_scalar(&self.active_epoch.ends_at, &self.active_epoch.started_at)?;
 
-                let emission_rate_duration_scalar = match duration {
-                    Duration::Height(h) => h,
-                    Duration::Time(t) => t,
-                };
+                let emission_rate_duration_scalar = get_duration_scalar(&duration);
 
                 amount
-                    .checked_multiply_ratio(epoch_duration, emission_rate_duration_scalar)
+                    .checked_multiply_ratio(epoch_duration_scalar, emission_rate_duration_scalar)
                     .map_err(|e| StdError::generic_err(e.to_string()))
             }
         }