Challenge #64

What does this code do?

An array of array[x][y] form is accessed here. Try to determine the dimensions of the array, at least partially, by finding y.

_array$ = 8
_x$ = 12
_y$ = 16
_f  PROC
    mov eax, DWORD PTR _x$[esp-4]
    mov edx, DWORD PTR _y$[esp-4]
    mov ecx, eax
    shl ecx, 4
    sub ecx, eax
    lea eax, DWORD PTR [edx+ecx*8]
    mov ecx, DWORD PTR _array$[esp-4]
    fld QWORD PTR [ecx+eax*8]
    ret 0
_f  ENDP

At first I think there is a mistake in the question. Because I only see three variables here, one for array address, the one x and one y, so I assume it's actually a 2d array of double, not a 3d as in "An array of array[x][y]".

Then I was stuck because eventually the program loads array[8y+192x], and x and y can be anything.

So I figured this must be a 3d array of double, with the third dimension given. I still couldn't figure it out so I tried to write my own program and use Godbolt to give me assembly. After a few trials I got something pretty close to the original program:

Something close

However I'm still having difficulty to match my program with the original question. I think I'm pretty close but how do I proceed from here? I have a hunch that y is also 24 in the original question, but not 100% sure.

Challenge #64

What does this code do?

An array of array[x][y] form is accessed here. Try to determine the dimensions of the array, at least partially, by finding y.

_array$ = 8
_x$ = 12
_y$ = 16
_f  PROC
    mov eax, DWORD PTR _x$[esp-4]
    mov edx, DWORD PTR _y$[esp-4]
    mov ecx, eax
    shl ecx, 4
    sub ecx, eax
    lea eax, DWORD PTR [edx+ecx*8]
    mov ecx, DWORD PTR _array$[esp-4]
    fld QWORD PTR [ecx+eax*8]
    ret 0
_f  ENDP

At first I think there is a mistake in the question. Because I only see three variables here, one for array address, the one x and one y, so I assume it's actually a 2d array of double, not a 3d as in "An array of array[x][y]".

Then I was stuck because eventually the program loads array[8y+192x], and x and y can be anything.

So I figured this must be a 3d array of double, with the third dimension given. I still couldn't figure it out so I tried to write my own program and use Godbolt to give me assembly. After a few trials I got something pretty close to the original program:

Something close

However I'm still having difficulty to match my program with the original question. I think I'm pretty close but how do I proceed from here? I have a hunch that y is also 24 in the original question, but not 100% sure.