bspline bits and pieces #1426

Job	Run time
macos-latest: clang++ Release Threads	2m 4s
macos-latest: clang++ Release OneTBB	3m 18s
macos-latest: clang++ Release PaRSEC	3m 2s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	54s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	2m 26s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	3m 17s
macos-latest: clang++ Debug Threads	2m 0s
macos-latest: clang++ Debug OneTBB	5m 59s
macos-latest: clang++ Debug PaRSEC	3m 59s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	40s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	2m 30s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	3m 22s
	33m 31s

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