section .text
;arguments: rdi, rsi, rdx, rcx, r8, r9
;callee-saved: rbx, rbp, rsp, r12-r15
;left-free r10-r11 ||maybe ^r12-r15^
string_length:
 xor rax, rax
 .loop:
 cmp byte[rdi + rax], 0
 jz .string_length_ret
 inc rax
 jmp .loop
 .string_length_ret:
 ret
print_string:
 call string_length
 mov rsi, rdi
 mov rdx, rax
 mov rax, 1
 mov rdi, 1
 syscall
 ret
print_char:
push rdi
mov rdi, rsp
call print_string
pop rdi
ret
print_newline:
 mov rdi, 0xA
 call print_char
 ret
print_uint:
 push 0
 mov rsi, rsp
 times 8 push 0 ; creating buffer on stack
 mov rax, rdi ; devidend
 mov rdx, 0 ; end of the future string
 mov [rsi], rdx
 dec rsi
 .loop:
 mov rbx, 10 ; devider
 mov rdx, 0 ; remainder
 div rbx ; rax div rbx
 add rdx, 0x30 ; add 0x30 so that number matches it's code in ASCII
 mov [rsi], dl ; move to buffer
 dec rsi
 cmp rax, 0 ; check if number has ended
 jnz .loop
 inc rsi
 mov rdi, rsi ; pass string address on stack as argument to print_string
 call print_string
 times 9 pop rax ; restore rsp
 ret
print_int: ;wtf
 mov rax, rdi
 cmp rax, 0
 jl .neg
 call print_uint
 jmp .end
 .neg:
 mov rdi, '-'
 push rax
 call print_char
 pop rax
 neg rax
 mov rdi, rax
 call print_uint
 .end:
 ret
; parameters: rdi, rsi - pointers to strings
; returns rax: 1 if string are equal, 0 if not
string_equals:
 xor rcx, rcx
 .string_equals_loop:
 mov r10b, [rdi+rcx] ; maybe byte
 mov r11b, [rsi+rcx]
 cmp r10b, r11b
 jne .string_equals_fail
 inc rcx
 test r10b, r10b
 jz .string_equals_null_check
 jmp .string_equals_loop
 .string_equals_null_check:
 test r11b, r11b
 jnz .string_equals_fail
 mov rax, 1
 ret
 .string_equals_fail:
 mov rax, 0
 ret
; uses: rax, rdi, rdx, rsi
read_char:
 xor rax, rax ; syscall #1 read
 xor rdi, rdi; stdin $0
 mov rdx, 1 ; read 1 byte
 push rax ; reserve place on stack for input
 mov rsi, rsp ; save char on stack
 syscall
 pop rax ; return char in rax
 ret
; arguments: rdi - buffer address, rsi - buffer size
; uses: rcx
; returns rax: buffer address; rdx: word length
read_word:
 push r12 ; save used registers
 push r13
 mov r12, rdi ; move buffer address and buffer size to callee-saved regs
 mov r13, rsi ; to avoid pushing and popping them later
 .read_word_skip_whitespaces:
 call read_char
 cmp al, 0x9 ; tabulation
 je .read_word_skip_whitespaces
 cmp al, 0x10 ; line break
 je .read_word_skip_whitespaces
 cmp al, 0x20 ; space
 je .read_word_skip_whitespaces
 mov rcx, -1 ; initialize rcx with -1
 .read_word_reading_chars:
 inc rcx ; increase the letter counter
 cmp al, 0 ; check for null-termination
 je .read_word_success
 cmp al, 0x20 ; check for space after word
 je .read_word_success
 mov [r12+rcx], al ; move the result of read_char to buffer
 cmp r13, rcx ; check if letter count is bigger than buffer size
 jbe .read_word_fail
 push rcx
 call read_char ; read next char
 pop rcx
 jmp .read_word_reading_chars
 .read_word_fail:
 mov rax, 0
 pop r13
 pop r12
 mov rdx, rcx
 ret
 .read_word_success:
 mov byte[r12+rcx], 0
 mov rax, r12 ; return buffer address or 0
 pop r13 ; restore used registers
 pop r12
 mov rdx, rcx
 ret
; argmunets: rdi - pointer to string
; returns rax: number, rdx : length
parse_uint:
 xor rsi, rsi
 xor rcx, rcx
 xor rax, rax
 mov r10, 10
 .parse_uint_loop:
 mov sil, [rdi+rcx]
 cmp sil, 0x30
 jb .parse_uint_ret
 cmp sil, 0x39
 ja .parse_uint_ret
 sub sil, 0x30
 mul r10
 add rax, rsi
 inc rcx
 jmp .parse_uint_loop
 .parse_uint_ret:
 mov rdx, rcx
 ret
; arguments: rdi - pointer to string
; returns rax: number; rdx: length
parse_int:
 cmp byte[rdi], '-'
 je .parse_int_negative
 call parse_uint
 ret
 .parse_int_negative:
 inc rdi
 call parse_uint
 test rdx, rdx
 jz .parse_int_ret
 neg rax
 inc rdx
 .parse_int_ret:
 ret
; parameters: rdi - pointer to string,
; rsi - pointer to buffer,
; rdx - buffer length
; returns pointer to buffer or 0 if failed
string_copy:
 xor r10, r10
 push rsi
 push rdi
 push rdx
 call string_length
 pop rdx
 pop rdi
 pop rsi
 inc rax
 cmp rdx, rax
 jl .string_copy_fail
 xor rcx, rcx
 .loop:
 mov r10, [rdi+rcx]
 mov [rsi+rcx], r10
 inc rcx
 dec rax
 jnz .loop
 jmp .string_copy_end

 .string_copy_fail:
 mov rax, 0
 .string_copy_end:
 ret