  In this paper, we report the results obtained from the acceleration of
multi-binary64-type multiple precision matrix multiplication with AVX2. We
target double-double (DD), triple-double (TD), and quad-double (QD) precision
arithmetic designed by certain types of error-free transformation (EFT)
arithmetic. Furthermore, we implement SIMDized EFT functions, which
simultaneously compute with four binary64 numbers on x86_64 computing
environment, and by using help of them, we also develop SIMDized DD, TD, and QD
additions and multiplications. In addition, AVX2 load/store functions were
adopted to efficiently speed up reading and storing matrix elements from/to
memory. Owing to these combined techniques, our implemented multiple precision
matrix multiplications have been accelerated more than three times compared
with non-accelerated ones. Our accelerated matrix multiplication modifies the
performance of parallelization with OpenMP.
