finit ; Initialize the FPU.
fldpi ; Load pi into st(0).
pushd 180
fild DWORD PTR [esp] ; Load 180 into st(0). Pi is now st(1).
fdiv ; Divide pi by 180, store result in st(0).
fld oldFovValue ; Load the old FOV into st(0). Move the divided result into st(1).
fmul ; Multiply the old FOV value by st(1) and store it in st(0).
pushd 2
fild DWORD PTR [esp]
fdiv
fptan
fstp st
fild aspect1
fild aspect2
fdiv
fmul
fld1
fpatan
pushd 2
fild DWORD PTR [esp]
fmul
pushd 180
fild DWORD PTR [esp]
fldpi
fdiv
fmul
fstp newFovValue
add esp,16