refactor: clean up repository layout

1 files changed, 324 insertions, 0 deletions

diff --git a/2025/day2.asm b/2025/day2.asm
new file mode 100644
index 0000000..987fbf9
--- /dev/null
+++ b/2025/day2.asm
@@ -0,0 +1,324 @@
+; Advent of Code 2025 – Day 2
+
+bits 64
+default rel
+
+global _start
+
+%include "utils/io.asm"
+%include "utils/parse.asm"
+
+section .data
+    input_path db "input/day2.txt", 0
+
+    label1 db "Part 1: ", 0
+    label2 db "Part 2: ", 0
+
+section .bss
+    buffer       resb 4096
+    line_buffer   resb 65536
+    line_len      resd 1
+
+    sum1         resq 1
+    sum2         resq 1
+
+section .text
+
+_start:
+    mov     rax, SYS_OPEN
+    mov     rdi, input_path
+    mov     rsi, O_RDONLY
+    xor     rdx, rdx
+    syscall
+
+    mov     r12, rax  ; file descriptor
+    mov     dword [line_len], 0
+
+read_loop:
+    mov     rax, SYS_READ
+    mov     rdi, r12
+    mov     rsi, buffer
+    mov     rdx, 4096
+    syscall
+
+    cmp     rax, 0
+    jle     eof
+
+    mov     rdi, buffer
+    mov     rbp, rax
+
+scan_chunk:
+    cmp     rbp, 0
+    je      read_loop
+
+    mov     al, [rdi]
+
+    cmp     al, 13
+    je      skip_cr
+
+    cmp     al, 10
+    je      end_line
+
+    mov     edx, [line_len]
+    cmp     edx, 65535
+    jae     skip_store
+    mov     [line_buffer+rdx], al
+    inc     edx
+    mov     [line_len], edx
+
+skip_store:
+    inc     rdi
+    dec     rbp
+    jmp     scan_chunk
+
+skip_cr:
+    inc     rdi
+    dec     rbp
+    jmp     scan_chunk
+
+end_line:
+    mov     edx, [line_len]
+    mov     byte [line_buffer+rdx], 0
+
+    cmp     edx, 0
+    je      clear_line
+
+    push    rdi
+    mov     rsi, line_buffer
+    call    handle_line
+    pop     rdi
+
+clear_line:
+    mov     dword [line_len], 0
+    inc     rdi
+    dec     rbp
+    jmp     scan_chunk
+
+eof:
+    ; process final partial line if needed
+    mov     edx, [line_len]
+    cmp     edx, 0
+    jle     print_results
+
+    mov     byte [line_buffer+rdx], 0
+    mov     rsi, line_buffer
+    call    handle_line
+
+print_results:
+    mov     rcx, label1
+    call    print_string
+    mov     rax, [sum1]
+    call    print_int64
+    call    print_newline
+
+    mov     rcx, label2
+    call    print_string
+    mov     rax, [sum2]
+    call    print_int64
+    call    print_newline
+
+    mov     rax, SYS_CLOSE
+    mov     rdi, r12
+    syscall
+
+    mov     rax, SYS_EXIT
+    xor     rdi, rdi
+    syscall
+
+; parse "A-B,C-D,..."l, RSI = pointer to line
+; uses r13 = current ID, r14 = end of range
+handle_line:
+next_range:
+    ; parse start
+    call    parse_u64
+    mov     r13, rax
+
+    cmp     byte [rsi], '-'
+    jne     done_line
+    inc     rsi
+
+    ; parse end
+    call    parse_u64
+    mov     r14, rax
+
+range_loop:
+    cmp     r13, r14
+    jg      after_range
+
+    ; Save RSI (line pointer) across the checks,
+    ; because number_to_string / check_invalid* use RSI
+    push    rsi
+
+    ; Part 1: exact AA
+    mov     rax, r13
+    call    check_invalid1
+    test    rax, rax
+    jz      .skip_p1
+    add     qword [sum1], r13
+.skip_p1:
+    ; Part 2: any repeating block >= 2
+    mov     rax, r13
+    call    check_invalid2
+    test    rax, rax
+    jz      .skip_p2
+    add     qword [sum2], r13
+.skip_p2:
+    pop     rsi  ; restore line pointer
+
+    inc     r13
+    jmp     range_loop
+
+after_range:
+    cmp     byte [rsi], ','
+    jne     done_line
+    inc     rsi
+    jmp     next_range
+
+done_line:
+    ret
+
+; number_to_string: convert RAX to decimal ASCII, MSB-first
+;   Output:
+;     RSI = pointer to first digit
+;     ECX = length
+number_to_string:
+    mov     rdi, number_buffer+31
+    mov     byte [rdi], 0  ; terminator (for convenience)
+    dec     rdi
+
+    cmp     rax, 0
+    jne     .conv
+
+    ; handle zero
+    mov     byte [rdi], '0'
+    mov     rsi, rdi
+    mov     ecx, 1
+    ret
+
+.conv:
+    mov     rbx, 10
+.next_digit:
+    xor     rdx, rdx
+    div     rbx  ; RAX = quotient, RDX = remainder
+    add     dl, '0'
+    mov     [rdi], dl
+    dec     rdi
+    test    rax, rax
+    jnz     .next_digit
+
+    inc     rdi  ; now RDI points to first digit
+    mov     rsi, rdi
+    mov     rdx, number_buffer+31
+    sub     rdx, rsi  ; RDX = length
+    mov     ecx, edx
+    ret
+
+; check_invalid1: "AA" pattern
+;   RAX = number
+;   Returns RAX = 1 if digits == A A, else 0
+check_invalid1:
+    push    rbx
+    push    rdx
+
+    call    number_to_string  ; RSI=string, ECX=len
+    mov     eax, ecx          ; EAX = len
+
+    cmp     eax, 2
+    jl      .no1
+
+    test    eax, 1
+    jnz     .no1  ; odd length => cannot be AA
+
+    shr     eax, 1    ; half = len/2
+    mov     r8d, eax  ; half
+    xor     r9d, r9d  ; i = 0
+
+.loop1:
+    cmp     r9d, r8d
+    jge     .yes1
+
+    ; s[i]
+    mov     rdx, r9
+    movzx   eax, byte [rsi + rdx]
+
+    ; s[i+half]
+    mov     rdx, r9
+    add     rdx, r8
+    movzx   ebx, byte [rsi + rdx]
+
+    cmp     eax, ebx
+    jne     .no1
+
+    inc     r9d
+    jmp     .loop1
+
+.yes1:
+    mov     rax, 1
+    jmp     .ret1
+
+.no1:
+    xor     rax, rax
+
+.ret1:
+    pop     rdx
+    pop     rbx
+    ret
+
+; check_invalid2: any repeating block >= 2
+;   RAX = number
+;   Returns RAX = 1 if string is some A repeated k>=2 times
+check_invalid2:
+    push    rbx
+    push    rdx
+
+    call    number_to_string  ; RSI=string, ECX=len
+    mov     r11d, ecx         ; n = length
+
+    cmp     r11d, 2
+    jb      .no2
+
+    mov     r8d, 1  ; m = 1 (candidate period)
+.outer:
+    cmp     r8d, r11d
+    jge     .no2
+
+    ; if n % m != 0 => cannot tile
+    mov     eax, r11d
+    xor     edx, edx
+    div     r8d  ; EAX=q, EDX=r
+    test    edx, edx
+    jnz     .next_m
+
+    mov     r9d, r11d
+    sub     r9d, r8d    ; limit = n - m
+    xor     r10d, r10d  ; i = 0
+.inner:
+    cmp     r10d, r9d
+    jge     .yes2  ; all positions checked
+
+    ; s[i]
+    mov     rdx, r10
+    movzx   eax, byte [rsi + rdx]
+
+    ; s[i+m]
+    mov     rdx, r10
+    add     rdx, r8
+    movzx   ebx, byte [rsi + rdx]
+
+    cmp     eax, ebx
+    jne     .next_m
+
+    inc     r10d
+    jmp     .inner
+.yes2:
+    mov     rax, 1
+    jmp     .ret2
+.next_m:
+    inc     r8d
+    jmp     .outer
+.no2:
+    xor     rax, rax
+.ret2:
+    pop     rdx
+    pop     rbx
+    ret