Use sparse array for cell position caches#1312

Merged

wuweiweiwu merged 2 commits intobvaughn:masterfrom trxcllnt:perf/use-llv

May 3, 2019

+71-117

Commits on Jan 27, 2019

swap hash-based cell position cache and binary search for constant-time sparse array cache
trxcllnt
committed
Guard against incomplete cell measurement
trxcllnt
committed