I had reason to dig up some information on the history of SPICE, and among other things learned that HSPICE is really Hailey-SPICE, from Shawn and Kim Hailey, who are twins and who started Meta software. This is a long -- but interesting -- interview with them:
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What they don't mention in there is that, yeah, "their own" SPICE ran at
6x-10x the speed of "regular" SPICE, but they started by taking the Berkeley SPICE 2E source code and adding some rather obvious vector optimizations based on the fact that they were running their program on a time-shared Cray, which could perform vector operations in hardware. Still, that was during the "wild wild west" stages of Silicon Valley, and it's quite impressive.
---Joel