public int calculateIndexPos(final long logIndex) {
        return (int) (this.header.getHeaderSize() + (logIndex - getFirstLogIndex() + 1) * getIndexSize());
    }
@return the IndexEntry's phyPosition in this IndexFile
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/file/index/IndexFile.java