feat: Use raw density in minVolume calculation and fix density calcul…

…ation in unpackLocalConfig function.

.changeset/brave-ads-end.md

@@ -0,0 +1,5 @@
+---
+"@mangrovedao/mgv": patch
+---
+
+Fix density by using the same algorithm as from the chain

src/lib/density.ts

@@ -48,6 +48,21 @@ export function formatDensity(density: number): bigint {
   return BigInt((exponent << 2) | mantissa)
 }
 
+const SUBNORMAL_LIMIT = 0b111n
+
+export function rawDensityTo96X32(rawDensity: bigint): bigint {
+  if (rawDensity <= SUBNORMAL_LIMIT) {
+    return rawDensity & 0b11n
+  }
+  const shift = (rawDensity >> 2n) - 2n
+  return ((rawDensity & 0b11n) | 0b100n) << shift
+}
+
+export function multiplyUpRawDensity(rawDensity: bigint, m: bigint): bigint {
+  const part = m * rawDensityTo96X32(rawDensity)
+  return (part >> 32n) + (part % (2n << 32n) === 0n ? 0n : 1n)
+}
+
 export function multiplyDensity(density: number, b: bigint, up = true): bigint {
   const roundMethod = up ? Math.ceil : Math.round
   return BigInt(roundMethod(Number(b) * density))
@@ -60,5 +75,5 @@ export function multiplyDensity(density: number, b: bigint, up = true): bigint {
  * @returns the minimum volume required to execute the offer.
  */
 export function minVolume(config: LocalConfig, gasreq: bigint): bigint {
-  return multiplyDensity(config.density, gasreq + config.offer_gasbase)
+  return multiplyUpRawDensity(config.rawDensity, gasreq + config.offer_gasbase)
 }

src/lib/local.test.ts

@@ -15,6 +15,7 @@ describe('local', () => {
       level1: 48n,
       root: 2n,
       offer_gasbase: 300_000n,
+      rawDensity: 273n,
       lock: false,
       last: 8698n,
     }

src/lib/local.ts

@@ -47,7 +47,8 @@ export function unpackLocalConfig(_config: bigint): LocalConfig {
   config >>= level3_bits
   const binPosInLeaf = config & mask(binPosInLeaf_bits)
   config >>= binPosInLeaf_bits
-  const density = parseDensity(config & mask(density_bits))
+  const rawDensity = config & mask(density_bits)
+  const density = parseDensity(rawDensity)
   config >>= density_bits
   const fee = config & mask(fee_bits)
   config >>= fee_bits
@@ -56,6 +57,7 @@ export function unpackLocalConfig(_config: bigint): LocalConfig {
     active: active === 1n,
     fee,
     density,
+    rawDensity,
     binPosInLeaf,
     level3,
     level2,

src/types/lib.ts

@@ -26,6 +26,7 @@ export type LocalConfig = {
   active: boolean
   fee: bigint
   density: number
+  rawDensity: bigint
   binPosInLeaf: bigint
   level3: bigint
   level2: bigint