Simplify alloc size calculation

4 jobs for master in 1 minute and 14 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #420847
amd64 debian
build-debian

00:00:33

passed #420848
macos
build-macos

00:01:07

passed #420850
amd64 docker
build-win32

00:01:11

passed #420849
amd64 docker
build-win64

00:01:14