Faster truncated integer multiplication

Abstract

We present new algorithms for computing the low $n$ bits or the high $n$ bits of the product of two $n$-bit integers. We show that these problems may be solved in asymptotically 75% of the time required to compute the full $2n$-bit product, assuming that the underlying integer multiplication algorithm relies on computing cyclic convolutions of real sequences.

32 pages. Improved exposition, updated timings