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basic rate-limited hole #218

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basic rate-limited hole #218

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43 changes: 36 additions & 7 deletions src/dog.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,11 @@ contract Dog {
uint256 chop; // Liquidation Penalty [wad]
uint256 hole; // Max DAI needed to cover debt+fees of active auctions per ilk [rad]
uint256 dirt; // Amt DAI needed to cover debt+fees of active auctions per ilk [rad]
uint256 trid; // Amt of dirt dug by auctions. [rad]
// Packed in to a single slot to minimze gas costs.
uint224 clod; // Amount of dirt to remove per time quantum [rad]
uint32 qntm; // Time between removal of clods [seconds]
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how about removing this and setting clod in a per-second basis to save some gas?

uint256 last; // Timstamp of most recent dirt reduction [Unix epoch]
}

VatLike immutable public vat; // CDP Engine
Expand Down Expand Up @@ -112,6 +117,10 @@ contract Dog {
function min(uint256 x, uint256 y) internal pure returns (uint256 z) {
z = x <= y ? x : y;
}
function min(uint256 x, uint256 y, uint256 z) internal pure returns (uint256 w) {
w = x <= y ? x : y;
if (z < w) w = z;
}
function add(uint256 x, uint256 y) internal pure returns (uint256 z) {
require((z = x + y) >= x);
}
Expand Down Expand Up @@ -195,15 +204,36 @@ contract Dog {
uint256 rate;
uint256 dust;
{
uint256 spot;
(,rate, spot,, dust) = vat.ilks(ilk);
require(spot > 0 && mul(ink, spot) < mul(art, rate), "Dog/not-unsafe");
{
uint256 spot;
(,rate, spot,, dust) = vat.ilks(ilk);
require(spot > 0 && mul(ink, spot) < mul(art, rate), "Dog/not-unsafe");
}

uint256 _Dirt = Dirt;
{
// Risk of overflow should be extremely small, even if milk.last = 0;
// can anyway be made less likely to overflow with a little more work.
uint256 pile = mul(sub(block.timestamp, milk.last) / milk.qntm, milk.clod);
pile = min(milk.dirt, milk.trid, pile);
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given trid <= dirt, why is dirt needed here?

if (pile > 0) {
milk.trid = sub(milk.trid, pile);
milk.dirt = sub(milk.dirt, pile); // In principle safe if trid <= dirt can be formally verified.
_Dirt = sub(_Dirt, pile); // In principle safe is dirt <= Dirt can be formally verified.
}
}

// Get the minimum value between:
// 1) Remaining space in the general Hole
// 2) Remaining space in the collateral hole
require(Hole > Dirt && milk.hole > milk.dirt, "Dog/liquidation-limit-hit");
uint256 room = min(Hole - Dirt, milk.hole - milk.dirt);
require(Hole > _Dirt && milk.hole > milk.dirt, "Dog/liquidation-limit-hit");
uint256 room = min(Hole - _Dirt, milk.hole - milk.dirt);

// Commit trid, dirt, Dirt, and last updates to storage.
ilks[ilk].trid = milk.trid;
ilks[ilk].dirt = milk.dirt;
Dirt = _Dirt;
ilks[ilk].last = block.timestamp;

// uint256.max()/(RAD*WAD) = 115,792,089,237,316
dart = min(art, mul(room, WAD) / rate / milk.chop);
Expand Down Expand Up @@ -256,8 +286,7 @@ contract Dog {
}

function digs(bytes32 ilk, uint256 rad) external auth {
Dirt = sub(Dirt, rad);
ilks[ilk].dirt = sub(ilks[ilk].dirt, rad);
ilks[ilk].trid = add(ilks[ilk].trid, rad);
emit Digs(ilk, rad);
}

Expand Down
28 changes: 14 additions & 14 deletions src/test/clip.t.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -415,7 +415,7 @@ contract ClipperTest is DSTest {

function test_get_chop() public {
uint256 chop = dog.chop(ilk);
(, uint256 chop2,,) = dog.ilks(ilk);
(, uint256 chop2,,,,,,) = dog.ilks(ilk);
assertEq(chop, chop2);
}

Expand Down Expand Up @@ -729,15 +729,15 @@ contract ClipperTest is DSTest {

function test_Hole_hole() public {
assertEq(dog.Dirt(), 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);

dog.bark(ilk, me, address(this));

(, uint256 tab,,,,) = clip.sales(1);

assertEq(dog.Dirt(), tab);
(,,, dirt) = dog.ilks(ilk);
(,,, dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, tab);

bytes32 ilk2 = "silver";
Expand Down Expand Up @@ -770,8 +770,8 @@ contract ClipperTest is DSTest {
(, uint256 tab2,,,,) = clip2.sales(1);

assertEq(dog.Dirt(), tab + tab2);
(,,, dirt) = dog.ilks(ilk);
(,,, uint256 dirt2) = dog.ilks(ilk2);
(,,, dirt,,,,) = dog.ilks(ilk);
(,,, uint256 dirt2,,,,) = dog.ilks(ilk2);
assertEq(dirt, tab);
assertEq(dirt2, tab2);
}
Expand All @@ -783,7 +783,7 @@ contract ClipperTest is DSTest {
assertEq(_art(ilk, me), 100 ether);

assertEq(dog.Dirt(), 0);
(,uint256 chop,, uint256 dirt) = dog.ilks(ilk);
(,uint256 chop,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);

dog.bark(ilk, me, address(this));
Expand All @@ -799,7 +799,7 @@ contract ClipperTest is DSTest {
assertEq(_art(ilk, me), 100 ether - tab * WAD / rate / chop);

assertEq(dog.Dirt(), tab);
(,,, dirt) = dog.ilks(ilk);
(,,, dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, tab);
}

Expand All @@ -810,7 +810,7 @@ contract ClipperTest is DSTest {
assertEq(_art(ilk, me), 100 ether);

assertEq(dog.Dirt(), 0);
(,uint256 chop,, uint256 dirt) = dog.ilks(ilk);
(,uint256 chop,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);

dog.bark(ilk, me, address(this));
Expand All @@ -826,7 +826,7 @@ contract ClipperTest is DSTest {
assertEq(_art(ilk, me), 100 ether - tab * WAD / rate / chop);

assertEq(dog.Dirt(), tab);
(,,, dirt) = dog.ilks(ilk);
(,,, dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, tab);
}

Expand Down Expand Up @@ -867,7 +867,7 @@ contract ClipperTest is DSTest {
assertEq(top, 0);

assertEq(dog.Dirt(), 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);
}

Expand Down Expand Up @@ -895,7 +895,7 @@ contract ClipperTest is DSTest {
assertEq(top, 0);

assertEq(dog.Dirt(), 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);
}

Expand Down Expand Up @@ -923,7 +923,7 @@ contract ClipperTest is DSTest {
assertEq(top, ray(5 ether));

assertEq(dog.Dirt(), tab);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, tab);
}

Expand Down Expand Up @@ -953,7 +953,7 @@ contract ClipperTest is DSTest {

// All dirt should be cleared, since the auction has ended, even though < 100% of tab was collected
assertEq(dog.Dirt(), 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);
}

Expand Down Expand Up @@ -1391,7 +1391,7 @@ contract ClipperTest is DSTest {

// Assert that callback to clear dirt was successful.
assertEq(dog.Dirt(), 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(dirt, 0);

// Assert transfer of gem.
Expand Down
22 changes: 11 additions & 11 deletions src/test/dog.t.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ contract DogTest is DSTest {
vat.file(ilk, "dust", dust * RAD);
uint256 hole = 5 * THOUSAND;
dog.file(ilk, "hole", hole * RAD);
(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
uint256 artStart = hole * WAD * WAD / chop + dust * WAD - 1;
setUrn(WAD, artStart);
dog.bark(ilk, usr, address(this));
Expand All @@ -122,7 +122,7 @@ contract DogTest is DSTest {
// The full vault has been liquidated so as not to leave a dusty remnant,
// at the expense of slightly exceeding hole.
assertEq(art, 0);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertTrue(dirt > hole * RAD);
assertEq(dirt, artStart * RAY * chop / WAD);
}
Expand All @@ -132,15 +132,15 @@ contract DogTest is DSTest {
vat.file(ilk, "dust", dust * RAD);
uint256 hole = 5 * THOUSAND;
dog.file(ilk, "hole", hole * RAD);
(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
setUrn(WAD, hole * WAD * WAD / chop + dust * WAD);
dog.bark(ilk, usr, address(this));
assertTrue(!isDusty());
(, uint256 art) = vat.urns(ilk, usr);

// The vault remnant respects the dust limit, so we don't exceed hole to liquidate it.
assertEq(art, dust * WAD);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertTrue(dirt <= hole * RAD);
assertEq(dirt, hole * RAD * WAD / RAY / chop * RAY * chop / WAD);
}
Expand All @@ -150,7 +150,7 @@ contract DogTest is DSTest {
vat.file(ilk, "dust", dust * RAD);
uint256 Hole = 5 * THOUSAND;
dog.file("Hole", Hole * RAD);
(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
uint256 artStart = Hole * WAD * WAD / chop + dust * WAD - 1;
setUrn(WAD, artStart);
dog.bark(ilk, usr, address(this));
Expand All @@ -169,7 +169,7 @@ contract DogTest is DSTest {
vat.file(ilk, "dust", dust * RAD);
uint256 Hole = 5 * THOUSAND;
dog.file("Hole", Hole * RAD);
(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
setUrn(WAD, Hole * WAD * WAD / chop + dust * WAD);
dog.bark(ilk, usr, address(this));
assertTrue(!isDusty());
Expand Down Expand Up @@ -204,7 +204,7 @@ contract DogTest is DSTest {
setUrn(WAD, (HOLE - ROOM) * RAD / rate * WAD / CHOP);
dog.bark(ilk, usr, address(this));
assertEq(HOLE * RAD - dog.Dirt(), ROOM * RAD);
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
assertEq(HOLE * RAD - dirt, ROOM * RAD);

// Create a small vault
Expand All @@ -222,7 +222,7 @@ contract DogTest is DSTest {
// In fact, there is only room to create dusty auctions at this point.
assertTrue(dog.Hole() - dog.Dirt() < DUST_2 * RAD * CHOP / WAD);
uint256 hole;
(,, hole, dirt) = dog.ilks(ilk);
(,, hole, dirt,,,,) = dog.ilks(ilk);
assertTrue(hole - dirt < DUST_2 * RAD * CHOP / WAD);

// But...our Vault is small enough to fit in ROOM
Expand All @@ -248,12 +248,12 @@ contract DogTest is DSTest {
(, uint256 rate,,,) = vat.ilks(ilk);
assertEq(rate, (15 * RAY) / 10);

(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
setUrn(WAD, (hole - dust / 2) * RAD / rate * WAD / chop);
dog.bark(ilk, usr, address(this));

// Make sure any partial liquidation would be dusty (assuming non-dusty remnant)
(,,, uint256 dirt) = dog.ilks(ilk);
(,,, uint256 dirt,,,,) = dog.ilks(ilk);
uint256 room = hole * RAD - dirt;
uint256 dart = room * WAD / rate / chop;
assertTrue(dart * rate < dust * RAD);
Expand All @@ -274,7 +274,7 @@ contract DogTest is DSTest {
(, uint256 rate,,,) = vat.ilks(ilk);
assertEq(rate, (15 * RAY) / 10);

(, uint256 chop,,) = dog.ilks(ilk);
(, uint256 chop,,,,,,) = dog.ilks(ilk);
setUrn(WAD, (Hole - dust / 2) * RAD / rate * WAD / chop);
dog.bark(ilk, usr, address(this));

Expand Down