OUSD gas improvements

[naddison36]

Contract Changes

• Changes to the following OUSD functions
  • balanceOf
  • _creditsPerToken
  • _isNonRebasingAccount
  • _ensureRebasingMigration
  • _burn
  • _rebaseOptIn

The approach was to not change the storage structure. The improvements are from not re-reading storage slots or avoiding unnecessary storage reads.

Code Change Checklist

To be completed before internal review begins:

• The contract code is complete
• Executable deployment file
• Fork tests that test after the deployment file runs
• Unit tests *if needed
• The owner has done a full checklist review of the code + tests

Internal review:

• Two approvals by internal reviewers

Gas changes

balanceOf

Set .only in contracts/test/token/ousd.js

describe.only("Should measure gas of balanceOf from", async () => {

Before

Contract	Method	Min	Max	Avg	# calls
ERC20	balanceOf	28950	34016	31688	3

After

Contract	Method	Min	Max	Avg	# calls
ERC20	balanceOf	28967	33842	31515	3

transfer

Set .only in contracts/test/token/ousd.js

describe.only("Should transfer the correct amount from a", () => {

Before

Contract	Method	Min	Max	Avg	# calls
ERC20	transfer	64385	119947	100621	11 │
MockNonRebasing	transfer	60338	77545	66109	3 │

After

Contract	Method	Min	Max	Avg	# calls
ERC20	transfer	58967	119432	98769	11 │
MockNonRebasing	transfer	51929	74429	61229	3 │

changeSupply

Set .only in contracts/test/token/ousd.js

it.only("Should measure gas of changeSupply", async () => {

Before

Contract	Method	Min	Max	Avg	# calls
Echidna	changeSupply	-	-	48572	1 │

After

Contract	Method	Min	Max	Avg	# calls
Echidna	changeSupply	-	-	47883	1 │

[github-actions]

	Warnings
⚠️	👀 This PR needs at least 2 reviewers

Generated by 🚫 dangerJS against 5f54f83

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 53.12%. Comparing base (1fb5af0) to head (5f54f83).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
contracts/contracts/token/OUSD.sol	90.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2287      +/-   ##
==========================================
- Coverage   53.26%   53.12%   -0.15%     
==========================================
  Files          79       79              
  Lines        4089     4098       +9     
  Branches     1074     1074              
==========================================
- Hits         2178     2177       -1     
- Misses       1908     1918      +10     
  Partials        3        3              

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[sparrowDom]

LGTM.

The code is equivalent to the previous version of it, with slight differences in order which don't have functional impact

[clement-ux]

Only a single comment about a scenario that is very unlikely to happen (but not 100% impossible), otherwise everything looks really good to me 👍

[clement-ux]

Looks good to me 👍