[DO NOT MERGE] adds PoC model for vault share price valuation by Tapanito · Pull Request #6434 · XRPLF/rippled

Tapanito · 2026-02-26T15:26:49Z

Spec: XRPLF/XRPL-Standards#485

High Level Overview of Change

Context of Change

Type of Change

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to not work as expected)
Refactor (non-breaking change that only restructures code)
Performance (increase or change in throughput and/or latency)
Tests (you added tests for code that already exists, or your new feature included in this PR)
Documentation update
Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
Release

API Impact

Public API: New feature (new methods and/or new fields)
Public API: Breaking change (in general, breaking changes should only impact the next api_version)
libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
Peer protocol change (must be backward compatible or bump the peer protocol version)

codecov · 2026-02-26T15:47:11Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.8%. Comparing base (ba53026) to head (2d66c06).

Additional details and impacted files

@@                      Coverage Diff                       @@
##           tapanito/lending-fix-amendment   #6434   +/-   ##
==============================================================
  Coverage                            79.8%   79.8%           
==============================================================
  Files                                 848     848           
  Lines                               67761   67767    +6     
  Branches                             7571    7561   -10     
==============================================================
+ Hits                                54056   54069   +13     
+ Misses                              13705   13698    -7

see 15 files with indirect coverage changes

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ximinez

Partial review

src/test/basics/VaultSharePricing_test.cpp

ximinez

In addition to the comments below, I noticed there are a lot of places where you have comments describing the current state of the vault. e.g.

// Vault: assetsTotal=1000, omega=50 (loan outstanding), iota=100, sharesTotal=1000

I'd like to see those have actual BEAST_EXPECT checks. Either added, or replacing the comments, up to your judgement.

Partial review. Note to self: left off at testPaperLossThenActualDefault()

ximinez · 2026-02-27T22:09:29Z

src/test/basics/VaultSharePricing_test.cpp


    void
-    setInterestUnrealized(Number omega)
+    borrow(Number const& principal, Number const& interest)


ximinez · 2026-02-27T22:09:48Z

src/test/basics/VaultSharePricing_test.cpp

+        XRPL_ASSERT(
+            principal > 0 && interest >= 0,
+            "xrpl::Vault::borrow requires positive principal and non-negative interest");
+        XRPL_ASSERT(
+            principal <= assetsAvailable_,
+            "xrpl::Vault::borrow principal exceeds assets available");


Since you're in a test, instead of XRPL_ASSERT, use BEAST_EXPECT, here and in the other tests. And return early if it fails.

That's a good idea!

So I'm not sure I can do that, since the Vault has nothing to do with the test suite, and I cannot inherit from it, the best I can do is:

if (!suite_.expect( principal > 0 && interest >= 0 && (!extraInterest || *extraInterest >= 0), __FILE__, __LINE__)) return;

I could move the vault class logic into the test itself, if we really want to replace assertions with beast expect.

src/test/basics/VaultSharePricing_test.cpp

ximinez · 2026-02-27T22:50:06Z

src/test/basics/VaultSharePricing_test.cpp

-        // Deposit 95 assets: shares = floor(95 * 1000 / 950) = floor(100) = 100
-        auto const [shares, assets] = vault.deposit(STAmount{usd, 95});
+        // Deposit 95 assets: shares = floor(95 * 950 / 950) = floor(95) = 95
+        // actualAssets = 95 * 950 / 950 = 95


I have found that writing these kinds of equations out with units really helps as both error checking, and for comprehension. Especially over the long run when this may not be top of mind, and I'm looking at 950 / 950 and wondering "why is this not 1?". So, for this case:

// Deposit 95 assets: shares = floor(95 assets * 950 shares / 950 assets) = floor(95 shares) = 95 shares // actualAssets = 95 shares * 950 assets / 950 shares = 95 assets

Or to take it a step further, which is probably overkill:

// Deposit 95 assets: shares = floor(95 assets deposited * 950 shares total / 950 net assets) = floor(95 shares deposited) = 95 shares deposited // actualAssets = 95 shares deposited * 950 net assets / 950 total shares = 95 assets deposited

What do you think?

src/test/basics/VaultSharePricing_test.cpp

ximinez · 2026-02-27T23:22:16Z

src/test/basics/VaultSharePricing_test.cpp

+        auto const out = vault.redeem(STAmount{vault.shareAsset(), 1000}).value();
+        // Approximate bounds: should be within 10% of 0.001
+        BEAST_EXPECT(Number(out) > Number(9, -4));   // > 0.0009
+        BEAST_EXPECT(Number(out) < Number(11, -4));  // < 0.0011


Could you compute this as an exact value? In fact, I would expect this to be the exact amount that was deposited.

auto const expected = ( Number(1, 12) + 1 ) / ( Number(1, 15) + 1000 ); BEAST_EXPECT(expected == Number(1, -3)); BEAST_EXPECT(out == STAmount(usd, expected));

ximinez · 2026-02-27T23:38:55Z

src/test/basics/VaultSharePricing_test.cpp

+        // withdrawalNAV = 1100 - 100 - 500 = 500
+
+        // Hard default confirmed (hasPaperLoss=true):
+        // assetsTotal -= 500 → 600; omega -= 100 → 0; lossUnrealized -= 500 → 0


Suggested change

// assetsTotal -= 500 → 600; omega -= 100 → 0; lossUnrealized -= 500 → 0

// assetsTotal -= 1100 → 600; omega -= 100 → 0; lossUnrealized -= 500 → 0

ximinez · 2026-02-27T23:44:04Z

src/test/basics/VaultSharePricing_test.cpp

+        // Withdraw 0.0001 assets: shares = truncate(0.0001 * 1 / 1) = 0 → tecPRECISION_LOSS
+        BEAST_EXPECT(!vault.withdraw(STAmount{usd, 1, -4}));
+        BEAST_EXPECT(vault.withdraw(STAmount{usd, 1, -4}).error() == tecPRECISION_LOSS);


Suggested change

// Withdraw 0.0001 assets: shares = truncate(0.0001 * 1 / 1) = 0 → tecPRECISION_LOSS

BEAST_EXPECT(!vault.withdraw(STAmount{usd, 1, -4}));

BEAST_EXPECT(vault.withdraw(STAmount{usd, 1, -4}).error() == tecPRECISION_LOSS);

// Withdraw 0.0001 assets: shares = truncate(0.0001 * 1 / 1) = 0 → tecPRECISION_LOSS

auto const withdrawResult = vault.withdraw(STAmount{usd, 1, -4});

BEAST_EXPECT(!withdrawResult);

BEAST_EXPECT(withdrawResult.error() == tecPRECISION_LOSS);

ximinez · 2026-02-27T23:54:57Z

src/test/basics/VaultSharePricing_test.cpp

+            auto const ok = vault.redeem(STAmount{vault.shareAsset(), 200});
+            BEAST_EXPECT(ok.has_value());
+            BEAST_EXPECT(Number(ok.value()) == Number(200));
+        }


At this point assetsAvailable is 0, correct? Is it fair to allow one holder to remove all the available assets, and force everyone else to wait for the loan to be paid back (and hope it doesn't default)?

ximinez · 2026-02-27T23:57:32Z

src/test/basics/VaultSharePricing_test.cpp

+    {
+        return STAmount{shareAsset_, sharesTotal_};
+    }
+


I think it would be worth it to add STAmount depositNAV() const and STAmount withdrawNAV() const function. The functions could be used by depost() and withdraw(), but they could also be used in the tests where right now you have comments saying what it should be.

adds PoC model for vault share price valuation

1c7daa1

additional cleanup

9eecce6

ximinez requested changes Feb 27, 2026

View reviewed changes

src/test/basics/VaultSharePricing_test.cpp Show resolved Hide resolved

rewrites poc for clarity

2d66c06

ximinez requested changes Feb 28, 2026

View reviewed changes

	// assetsTotal -= 500 → 600; omega -= 100 → 0; lossUnrealized -= 500 → 0
	// assetsTotal -= 1100 → 600; omega -= 100 → 0; lossUnrealized -= 500 → 0

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Tapanito commented Feb 26, 2026

High Level Overview of Change

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codecov bot commented Feb 26, 2026 •

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