Modifying Chest Contents with SRM

hypothetical scenario. this is not a valid actor heap address.

chest is at 80100000
spawn variable is at actor+0x1C
so spawn variable is at 8010001C

the spawn variable is a 2 byte value that is passed into the Spawn_Actor function at spawn time.
this variable can contain verious information about an actor. it uses all 16 bits of this 2 byte number to store that information.
we are interested in the chest contents, which is stored in the bits shown below:

spawn var = 0000cccc ccc00000
where c is the contents

for more info on spawn variables, see the writeup here: https://wiki.cloudmodding.com/oot/Actor_List_(Variables)#Overview

to modify 8010001C directly with the x coordinate (where SRM starts modifying), you would need to be holding spawn variable -0x24
8010001C - 0x24 = 800FFFF8

but since actors on the heap are 10 byte aligned this doesn't work.
so 800FFFF0 will have to do

address of held actor is 800FFFF0
with SRM, you would start modifying at 800FFFF0+0x24 = 80100014

4 byte float for x @ 80100014
4 byte float for y @ 80100018
4 byte float for z @ 8010001C

32 bit z coordinate lines up with 16 bit spawn variable like so:
zzzz zzzz zzzz zzzz
ssss ssss uuuu uuuu
where z is z coordinate, s is spawn variable, and u is something irrelevant for the chest contents.
note that bad values for u, or the x/y/actor rotation can cause unwanted effects/crashes.

this means that the upper 2 bytes of the 4 byte z coordinate float are what is modifying the contents.
specifically these bits shown earlier:
0000cccc ccc00000 00000000 00000000