This paper presents a compression and decompression scheme based on run-length codes for reducing the amount of test data.We refer to this hybrid run-length codes

it has the excellent advantages of high compression ratios

robust and low area overhead.Since the compression ratios strongly depend on the strategy of mapping which doesn't care in the original test set to zeros or ones

we also present an Iterative Sort Filling algorithm to find the best assignment method which minimizes the total size of the test data and achieves higher compression ratio.The theoretical analysis and the experimental results for ISCAS 89 benchmark circuits demonstrated the compression efficiency of the proposed hybrid run-length codes and Iterative Sort Filling algorithm.