NationalSecurityAgency/ghidra · error · IllegalArgumentException

Cannot rewind a negative number

Error message

Cannot rewind a negative number

What it means

Sequence.rewind throws when called with a negative count. Rewinding means removing the given number of steps from the end of the sequence; a negative count is logically meaningless. The method modifies the sequence in place, reducing each step's tick count from the tail until the requested count is consumed.

Solutions

1. Clamp the count to zero before calling: rewind(Math.max(0, count))
2. Check the sign before calling: if (count >= 0) sequence.rewind(count)
3. If computing a delta between two sequences, ensure the result is non-negative or use Long.max(0, delta)

Example fix

// before
sequence.rewind(delta); // delta may be negative
// after
if (delta > 0) {
    sequence.rewind(delta);
}

long safeCount = Math.max(0, requestedCount);
if (safeCount > 0) {
    sequence.rewind(safeCount);
}

// N/A — primitive long, guard with range check

try {
    sequence.rewind(count);
} catch (IllegalArgumentException e) {
    // clamp count to 0 and retry, or report
    sequence.rewind(0);
}

When it happens

Trigger: Calling sequence.rewind(negativeNumber) directly, or calling it with a value computed from a subtraction that can go negative (e.g. rewind(this.getTotalTickCount() - other.getTotalTickCount()) when this has fewer ticks than other).

Common situations: Diffing two schedules and rewinding by the delta without clamping to zero. Using rewind in a loop where the count variable is decremented past zero by external logic.

Related errors

• The given prefix ( ) is not actually a prefix of this ( ).
• Cannot have instructions steps following p-code steps
• Thread must be given, e.g., 0:t1-3, since the last thread…
• Thread with key does not exist in given trace
• Arrays must be the same length

AI-assisted analysis of NationalSecurityAgency/ghidra@d5f144c24d (2026-08-14). Data as JSON: /api/errors/9d369fb549c24818. Report an issue: GitHub.

Appendix: source

Thrown at Ghidra/Debug/Framework-TraceModeling/src/main/java/ghidra/trace/model/time/schedule/Sequence.java:188

		for (; toRemove > 0; toRemove--) {
			steps.remove(steps.size() - 1);
		}
	}

	/**
	 * Rewind this sequence the given step count
	 * 
	 * <p>
	 * This modifies the sequence in place, removing the given count from the end of the sequence.
	 * Any step whose count is reduced to 0 as a result of rewinding is removed entirely from the
	 * sequence. Note that each sleigh step (modification) counts as one step when rewinding.
	 * 
	 * @param count the step count to rewind
	 * @return if count exceeds the steps of this sequence, the (positive) difference remaining
	 */
	public long rewind(long count) {
		if (count < 0) {
			throw new IllegalArgumentException("Cannot rewind a negative number");
		}
		while (!steps.isEmpty()) {
			int lastIndex = steps.size() - 1;
			count = steps.get(lastIndex).rewind(count);
			if (count >= 0) {
				steps.remove(lastIndex);
			}
			if (count <= 0) {
				break;
			}
		}
		return Long.max(0, count);
	}

	/**
	 * Drop the last step from this sequence
	 * 
	 * @return the sequence with the last step removed

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