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export function applyGitDelta(base: Uint8Array, delta: Uint8Array): Uint8Array {
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  let pos = 0;
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  const readVarint = () => {
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    let out = 0;
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    let shift = 0;
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    while (true) {
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      if (pos >= delta.length) throw new Error("delta:truncated-varint");
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      const byte = delta[pos++];
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      out |= (byte & 0x7f) << shift;
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      if (!(byte & 0x80)) return out;
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      shift += 7;
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    }
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  };
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  const baseSize = readVarint();
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  const resultSize = readVarint();
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  if (baseSize !== base.length) throw new Error("delta:base-size-mismatch");
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  const out = new Uint8Array(resultSize);
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  let outPos = 0;
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  while (pos < delta.length) {
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    const opcode = delta[pos++];
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    if (opcode & 0x80) {
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      let copyOffset = 0;
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      let copySize = 0;
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      if (opcode & 0x01) copyOffset |= delta[pos++];
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      if (opcode & 0x02) copyOffset |= delta[pos++] << 8;
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      if (opcode & 0x04) copyOffset |= delta[pos++] << 16;
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      if (opcode & 0x08) copyOffset |= delta[pos++] << 24;
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      if (opcode & 0x10) copySize |= delta[pos++];
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      if (opcode & 0x20) copySize |= delta[pos++] << 8;
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      if (opcode & 0x40) copySize |= delta[pos++] << 16;
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      if (copySize === 0) copySize = 0x10000;
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      if (copyOffset < 0 || copyOffset + copySize > base.length) {
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        throw new Error("delta:copy-out-of-bounds");
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      }
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      out.set(base.subarray(copyOffset, copyOffset + copySize), outPos);
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      outPos += copySize;
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      continue;
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    }
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    if (opcode === 0) throw new Error("delta:invalid-opcode");
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    if (pos + opcode > delta.length) throw new Error("delta:insert-out-of-bounds");
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    out.set(delta.subarray(pos, pos + opcode), outPos);
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    outPos += opcode;
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    pos += opcode;
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  }
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  if (outPos !== out.length) throw new Error("delta:result-size-mismatch");
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  return out;
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}