Function commonPrefixLength

src/llm/cache-layout.ts:43–50

(a: Message[], b: Message[])

/** Number of leading messages that are byte-identical between two message arrays.
 *  This is the prefix the inference server can serve from KV cache. */
export function commonPrefixLength(a: Message[], b: Message[]): number {
  const n = Math.min(a.length, b.length);
  let i = 0;
  for (; i < n; i++) {
    if (serializeMessage(a[i]!) !== serializeMessage(b[i]!)) break;
  }
  return i;
}

/** Approximate character count of the first `n` messages (proxy for cached tokens). */
export function prefixChars(messages: Message[], n: number): number {