bits 64
global popcount
section .text

; prototype: unsigned long popcount(char*, int64_t);
popcount:
        push rbp
        mov rbp, rsp
        mov rcx, rsi
        shr rcx, 3
        mov rsi, rdi
        xor rax, rax

.cnt    popcnt rbx, [rsi]
        add rax, rbx
        add rsi, 8
        loop .cnt
          
        mov rsp, rbp
        pop rbp
        ret