.intel_syntax noprefix

.equ SYS_MMAP, 9
.equ SYS_MUNMAP, 11

.text
.globl nub_strlen
# func nub_strlen(string: cstring): u64
nub_strlen:
    test rdi, rdi
    jz null_string
    xor rax, rax
strlen_loop:
    cmp byte ptr [rdi + rax], 0
    je strlen_exit
    inc rax
    jmp strlen_loop
null_string:
    xor rax, rax
strlen_exit:
    ret

.text
.globl nub_cstring_to_string
# func nub_cstring_to_string(string: cstring): []u8
nub_cstring_to_string:
    push rbx
    push r12
    push r13

    mov rbx, rdi            # Save original pointer
    call nub_strlen
    mov r12, rax            # r12 = string length

    # Calculate total space needed: 8 bytes (length) + string length
    mov r13, r12
    add r13, 8              # r13 = total bytes needed

    # Round up to page size (4096 bytes) for mmap
    add r13, 4095           # Add page_size - 1
    and r13, -4096          # Align to page boundary

    mov rax, SYS_MMAP
    xor rdi, rdi            # addr = 0 (let kernel choose)
    mov rsi, r13            # length = aligned size
    mov rdx, 3              # prot = PROT_READ | PROT_WRITE
    mov r10, 34             # flags = MAP_PRIVATE | MAP_ANONYMOUS (0x22)
    mov r8, -1              # fd = -1
    xor r9, r9              # offset = 0
    syscall

    # Check if mmap failed
    cmp rax, -1
    je mmap_failed

    mov r13, rax            # r13 = pointer to mapped memory

    # Store length at beginning of mapped memory
    mov [r13], r12          # Store string length

    # Copy string data if not empty
    test r12, r12           # Check if length is 0
    jz copy_done

    lea rdi, [r13 + 8]
    mov rsi, rbx
    mov rcx, r12
    call nub_memcpy

copy_done:
    mov rax, r13
    jmp function_exit

mmap_failed:
    xor rax, rax

function_exit:
    pop r13
    pop r12
    pop rbx
    ret

.text
.globl nub_string_free
# func nub_string_free(string: []u8): void
nub_string_free:
    test rdi, rdi
    jz free_exit

    mov rsi, [rdi]
    add rsi, 8

    # Round up to page size
    add rsi, 4095
    and rsi, -4096

    mov rax, SYS_MUNMAP
    syscall
free_exit:
    ret