Support conversion between target and difficulty

packages/web3/src/utils/utils.test.ts

@@ -107,4 +107,39 @@ describe('utils', function () {
     check('00000000000a11fc7e30525ff1c2d783de3344b85a9c76abdd207ad8e1401566', 1, 2)
     check('00000000000d09d9f9cf3c3619ca18b84c44437d61cdf0b423831e23e1847e20', 0, 0)
   })
+
+  it('should convert between target and difficulty', () => {
+    const maxBigInt = 1n << 256n
+    for (let num = 1; num < 256; num += 1) {
+      const targetValue = 1n << BigInt(num)
+      const diff = maxBigInt / targetValue
+      const compactedTarget = utils.difficultyToTarget(diff)
+      expect(utils.targetToDifficulty(compactedTarget)).toEqual(diff)
+    }
+
+    expect(utils.targetToDifficulty('03010101')).toEqual(
+      1759945423332515547604927348026201994942774834186624170344224826469580800n
+    )
+    expect(
+      utils.difficultyToTarget(1759945423332515547604927348026201994942774834186624170344224826469580800n)
+    ).toEqual('03010101')
+    expect(utils.targetToDifficulty('10010000')).toEqual(87112285931760246646623899502532662132736n)
+    expect(utils.difficultyToTarget(87112285931760246646623899502532662132736n)).toEqual('10010000')
+    expect(utils.targetToDifficulty('12ffffff')).toEqual(5192297168019855896620738275246080n)
+    expect(utils.difficultyToTarget(5192297168019855896620738275246080n)).toEqual('12ffffff')
+    expect(utils.targetToDifficulty('20ffffff')).toEqual(1n)
+    expect(utils.difficultyToTarget(1n)).toEqual('20ffffff')
+    expect(utils.targetToDifficulty('1b01ae98')).toEqual(167344728152528n)
+    expect(utils.difficultyToTarget(167344728152528n)).toEqual('1b01ae98')
+
+    expect(() => utils.targetToDifficulty('1b01ae9')).toThrow(
+      'Invalid target 1b01ae9, expected a hex string of length 8'
+    )
+    expect(() => utils.targetToDifficulty('1b01ae988')).toThrow(
+      'Invalid target 1b01ae988, expected a hex string of length 8'
+    )
+    expect(() => utils.targetToDifficulty('1b01ae9z')).toThrow(
+      'Invalid target 1b01ae9z, expected a hex string of length 8'
+    )
+  })
 })

packages/web3/src/utils/utils.ts

@@ -112,6 +112,31 @@ export function isDevnet(networkId?: number): boolean {
   return networkId !== 0 && networkId !== 1
 }
 
+export function targetToDifficulty(compactedTarget: HexString): bigint {
+  if (!isHexString(compactedTarget) || compactedTarget.length !== 8) {
+    throw Error(`Invalid target ${compactedTarget}, expected a hex string of length 8`)
+  }
+  const size = hexToBinUnsafe(compactedTarget.slice(0, 2))[0]
+  const mantissa = BigInt('0x' + compactedTarget.slice(2))
+  const maxBigInt = 1n << 256n
+  const target = size <= 3 ? mantissa >> BigInt(8 * (3 - size)) : mantissa << BigInt(8 * (size - 3))
+  return maxBigInt / target
+}
+
+export function difficultyToTarget(diff: bigint): HexString {
+  const maxBigInt = 1n << 256n
+  const target = diff === 1n ? maxBigInt - 1n : maxBigInt / diff
+  const size = Math.floor((target.toString(2).length + 7) / 8)
+  const mantissa =
+    size <= 3
+      ? BigInt.asIntN(32, target) << BigInt(8 * (3 - size))
+      : BigInt.asIntN(32, target >> BigInt(8 * (size - 3)))
+  const mantissaBytes = Buffer.alloc(4)
+  mantissaBytes.writeInt32BE(Number(mantissa), 0)
+  const bytes = new Uint8Array([size, ...mantissaBytes.slice(1)])
+  return binToHex(bytes)
+}
+
 type _Eq<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2 ? true : false
 export type Eq<X, Y> = _Eq<{ [P in keyof X]: X[P] }, { [P in keyof Y]: Y[P] }>
 // eslint-disable-next-line @typescript-eslint/no-empty-function, @typescript-eslint/no-unused-vars