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FIP-05: Difficulty Adjustment

Author: Thiniboy
Status: Final
Created: 2025-07-18

Summary​

Adopt a per-block, Digishield-style difficulty retarget using an exponential moving average (EMA) toward the one-minute target spacing. The algorithm improves responsiveness to hashrate shocks while damping oscillations and reducing variance.

Motivation​

Long retarget windows allow exploitable oscillations and long periods of off-target difficulty. A per-block EMA responds quickly to changes while preserving stability.

Specification​

  • Target spacing T = 60 seconds.
  • At each block n, update an EMA of observed spacings with amplitude divisor 8 (effectively an 8-sample EWMA).
  • Apply bounded damping on each step to limit the effective spacing influence to the range [0.75·T, 1.5·T].
  • Compute the next target by scaling the previous target by the ratio of clamped spacing to T, subject to consensus limits.
  • Allow minimum-difficulty blocks when the observed spacing exceeds a chain-parameterized threshold (where enabled).
important

Activation (mainnet): block 115,000.

Rationale​

Per-block EMA reduces lag compared to long-window retargets while the clamp prevents over-reaction to outliers. Similar approaches were proven in other UTXO chains under the “Digishield” family.

Reference Implementation​

Implemented in go-flokicoin and enabled via chain parameters. See release 0.25.7-beta and consensus changes therein.

Inputs:
  T           := 60 seconds (target spacing)
  Divisor     := DigishieldAmplitudeDivisor (8 in Flokicoin)
  ClampMin    := 0.75 × T
  ClampMax    := 1.50 × T
  prevTarget  := last difficulty target (integer)
  actualSpan  := timestamp_n - timestamp_{n-1}

Algorithm:
  1. modulatedSpan ← T + (actualSpan - T) / Divisor
  2. modulatedSpan ← clamp(modulatedSpan, ClampMin, ClampMax)
  3. nextTarget ← prevTarget × modulatedSpan / T
  4. nextTarget ← min(nextTarget, PowLimit)

Result:
  Convert nextTarget back to compact bits for the header.

Note: when ReduceMinDifficulty is enabled, a separate rule mints a
minimum-difficulty block if actualSpan exceeds DigishieldLateBlockMultiple × T.
That shortcut is orthogonal to the per-block EMA above.