Decode and Store effect model Point

r6 seems to be 0? might be some kind of geometric transformer.

001a8bf8: 00a42823 subu r5,r5,r4                 b - a
001a8bfc: 00a60018 mult r5,r6                    c(b - a)
001a8c00: 00001012 mflo r2
001a8c04: 00021203 sra r2,r2,0x08                
001a8c08: 00441021 addu r2,r2,r4                 c(b - a) + r4 (often just stores a)
001a8c0c: 03e00008 jr r31
001a8c10: ace20000 sw r2,0x0000(r7)              store value in r2