Question about calminstructions

Hi all!
I ma trying to use calminstructions in fasmg to create some bytecode, but I ran into some problem. Firstly here the code:

Code:

element reg
element reg.r8  : reg + 0
element reg.r16 : reg + 1
element reg.r32 : reg + 2
element reg.r64 : reg + 3
element reg.f32 : reg + 4
element reg.f64 : reg + 5

repeat 32
        element r#%#b?  : reg.r8 + %
        element r#%#w?  : reg.r16 + %
        element r#%#d?  : reg.r32 + %
        element r#%#q?  : reg.r64 + %
        element r#%#f?  : reg.f32 + %
        element r#%#fd? : reg.f64 + %
end repeat

calminstruction parse_operand op
        local size_byte, second_byte
        local reg_index, reg_size
        compute reg_index, 0 scaleof op
        compute reg_size, 1 metadataof (1 metadataof op) - reg

        arrange size_byte, =db reg_size
        arrange second_byte, =db reg_index

        assemble size_byte
        assemble second_byte
end calminstruction

org 0
parse_operand r3f

In this code I have defined 32 registers, each of which can be used in 8, 16, 32 and 64-bit modes. Also here is calminstruction "parse_operand" which I use to parse register. This calminstruction must assemble two bytes: first byte defines size (8,16,32 or 64-bit) and second byte defines register index. In this example I use "parse_operand r3f", it compiles successful and first byte is correct. But second byte always zero and does not depend on register number. To get register number in "parse_operand" I use command "compute reg_index, 0 scaleof op", where I am wrong?