Negstore
From WikiManual
Converts the memory to its negative value.
examples:
Given 5 .up store
.up negstore same as *.up - .up store same as *.up -1 mult .up store is equal to -5
Given -5 .up store
.up negstore same as *.up - .up store same as *.up -1 mult .up store is equal to 5
