.intel_syntax noprefix

.text
.globl nub_string_length
# func nub_string_length(string: string): u64
nub_string_length:
    mov rsi, [rdi]  # Length of string in bytes
    
    add rdi, 8      # Start of bytes
    xor rax, rax    # Character count
    xor rdx, rdx    # Current byte position
    
    test rsi, rsi
    jz _done
    
_count_loop:
    cmp rdx, rsi
    jge _done
    
    mov dl, [rdi + rdx]
    and dl, 0b11000000
    cmp dl, 0b10000000
    je _skip_byte
    
    inc rax
    
_skip_byte:
    inc rdx
    jmp _count_loop
    
_done:
    ret