ScheduleUtils Code Style Findings

SUS-01C: Inefficient Cliff Total Evaluation

Type	Severity	Location
Gas Optimization		ScheduleUtils.sol:L80-L93

Description:

The total cliff amount evaluation occurs on each cliff addition and contains an expensive iteration of all cliff periods and their amounts.

Example:

Copy
51/**
52 * @dev Adds a cliff defined by *time* and *amount* to *schedule*
53 *
54 * *time* must be >= any existing cliff, >= schedule.startTime and <= schedule.endTime
55 * *amount* must be <= (schedule.totalAmount - total of existing cliffs)
56 */
57function addCliff(
58  Schedule storage schedule,
59  uint256 time,
60  uint256 amount
61) internal {
62  if (schedule.cliffCount == 0) {
63    require(time >= schedule.startTime, "Cliff before schedule start");
64  } else {
65    require(
66      time >= schedule.cliffs[schedule.cliffCount - 1].time,
67      "Cliffs not chronological"
68    );
69  }
70  require(time <= schedule.endTime, "Cliffs cannot end after schedule");
71  require(
72    allCliffAmounts(schedule) + amount <= schedule.totalAmount,
73    "cliff amounts exceed total"
74  );
75  schedule.cliffs[schedule.cliffCount].time = time;
76  schedule.cliffs[schedule.cliffCount].amount = amount;
77  schedule.cliffCount += 1;
78}
79
80/**
81 * @dev The sum of all cliff amounts in *schedule*
82 */
83function allCliffAmounts(Schedule storage schedule)
84  internal
85  view
86  returns (uint256)
87{
88  uint256 cliffAmounts;
89  for (uint256 i = 0; i < schedule.cliffCount; i++) {
90    cliffAmounts += schedule.cliffs[i].amount;
91  }
92  return cliffAmounts;
93}

Recommendation:

We advise the total to be tracked whenever a cliff is introduced instead, greatly optimizing the efficiency of the system.

Alleviation:

The total cliff amount is now correctly tracked in every addCliff operation rendering the calculation of it redundant.

SUS-02C: Inefficient Loop Limit Evaluations

Type	Severity	Location
Gas Optimization		ScheduleUtils.sol:L89, L104

Description:

The linked loop limit evaluations read a value from storage on each iteration.

Example:

Copy
98function cliffAmountsAvailable(Schedule storage schedule, uint256 atTime)
99  internal
100  view
101  returns (uint256)
102{
103  uint256 available = 0;
104  for (uint256 i = 0; i < schedule.cliffCount; i++) {

Recommendation:

We advise their limit to instead be cached to a local variable that is consequently utilized greatly optimizing their gas cost.

Alleviation:

The first loop was omitted as part of another exhibit and the second loop was optimized as advised thereby alleviating this exhibit.

SUS-03C: Inefficient Usage of Signed Integers

Type	Severity	Location
Gas Optimization		ScheduleUtils.sol:L135-L139

Description:

The linked statements make use of the int256 type to allow the subtraction to occur even when it goes to negative values in which case the value of 0 is yielded for linear amount available.

Example:

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135int256 rampTimeElapsed = int256(atTime) - int256(rampStartTime);
136return
137  rampTimeElapsed <= 0
138    ? 0
139    : (rampTotalAmount * uint256(rampTimeElapsed)) / rampTotalTime;

Recommendation:

We advise an if check to be utilized instead that checks whether atTime is greater-than (>) the value of rampStartTime in which case the value of zero is returned, reducing the complexity and gas cost of the statements.

Alleviation:

The code was updated to utilize the existing ternary operator instead with a different conditional optimizing the codebase.

SUS-04C: Inefficient mapping Lookups

Type	Severity	Location
Gas Optimization		ScheduleUtils.sol:L75, L76, L105, L106

Description:

The linked statements contain duplicate mapping entry lookups which could instead be cached to a local variable (i.e. for mapping(uint256 => Struct) foo the statements foo[0].a = 0; foo[0].b = 1; can be optimized to Struct storage bar = foo[0]; bar.a = 0; bar.b = 1;).

Example:

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75schedule.cliffs[schedule.cliffCount].time = time;
76schedule.cliffs[schedule.cliffCount].amount = amount;

Recommendation:

We advise optimizations to be applied as outlined in the description.

Alleviation:

The mapping lookups were only optimized for the first instance thereby partially alleviating this exhibit.

SUS-05C: Redundant Duplicate Value Reads

Type	Severity	Location
Gas Optimization		ScheduleUtils.sol:L62, L66, L75, L76, L77

Description:

The linked statements read schedule.cliffCount from storage multiple times redundantly.

Example:

Copy
57function addCliff(
58  Schedule storage schedule,
59  uint256 time,
60  uint256 amount
61) internal {
62  if (schedule.cliffCount == 0) {
63    require(time >= schedule.startTime, "Cliff before schedule start");
64  } else {
65    require(
66      time >= schedule.cliffs[schedule.cliffCount - 1].time,
67      "Cliffs not chronological"
68    );
69  }
70  require(time <= schedule.endTime, "Cliffs cannot end after schedule");
71  require(
72    allCliffAmounts(schedule) + amount <= schedule.totalAmount,
73    "cliff amounts exceed total"
74  );
75  schedule.cliffs[schedule.cliffCount].time = time;
76  schedule.cliffs[schedule.cliffCount].amount = amount;
77  schedule.cliffCount += 1;
78}

Recommendation:

We advise its value to be cached to a local variable optimizing the code's execution cost.

Alleviation:

The code was optimized in all instances except the first if conditional thereby partially alleviating this exhibit.