refactor: add day-4-8

1 files changed, 419 insertions, 0 deletions

diff --git a/aoc-2025/day6.asm b/aoc-2025/day6.asm
new file mode 100644
index 0000000..774ca4c
--- /dev/null
+++ b/aoc-2025/day6.asm
@@ -0,0 +1,419 @@
+; Advent of Code 2025 - Day 6
+
+bits 64
+default rel
+
+global _start
+
+%define SYS_EXIT   60
+%define SYS_READ   0
+%define SYS_WRITE  1
+%define SYS_OPEN   2
+%define SYS_CLOSE  3
+
+%define O_RDONLY   0
+%define STDOUT     1
+
+%define RAW_SIZE   1048576
+%define MAX_W      8192
+%define MAX_H      64
+%define GRID_SIZE  (MAX_W * MAX_H)
+
+section .data
+    input_path db "input/day6.txt", 0
+
+    newline    db 10
+
+    label1     db "Part 1: ", 0
+    label2     db "Part 2: ", 0
+
+section .bss
+    raw           resb RAW_SIZE
+    grid          resb GRID_SIZE   ; height x width, space-filled
+
+    raw_len       resq 1
+    width         resq 1
+    height        resq 1
+
+    blk_c0        resq 1           ; current block: columns [blk_c0, blk_c1)
+    blk_c1        resq 1
+    op            resq 1           ; 0 = add, 1 = mul, -1 = none
+
+    part1         resq 1
+    part2         resq 1
+
+    number_buffer resb 32
+
+section .text
+
+_start:
+    mov     rax, SYS_OPEN
+    mov     rdi, input_path
+    mov     rsi, O_RDONLY
+    xor     rdx, rdx
+    syscall
+    mov     r12, rax
+
+    xor     r13, r13
+read_loop:
+    mov     rax, SYS_READ
+    mov     rdi, r12
+    lea     rsi, [raw + r13]
+    mov     rdx, RAW_SIZE
+    sub     rdx, r13
+    syscall
+    cmp     rax, 0
+    jle     read_done
+    add     r13, rax
+    jmp     read_loop
+read_done:
+    mov     [raw_len], r13
+
+    mov     rax, SYS_CLOSE
+    mov     rdi, r12
+    syscall
+
+    ; width = length of the first line
+    xor     rcx, rcx
+width_scan:
+    cmp     rcx, [raw_len]
+    jge     width_done
+    mov     al, [raw + rcx]
+    cmp     al, 10
+    je      width_done
+    cmp     al, 13
+    je      width_done
+    inc     rcx
+    jmp     width_scan
+width_done:
+    mov     [width], rcx
+
+    ; height = number of lines (newlines, plus one if the last line has no newline)
+    xor     rcx, rcx
+    xor     r8, r8
+height_scan:
+    cmp     rcx, [raw_len]
+    jge     height_tail
+    mov     al, [raw + rcx]
+    cmp     al, 10
+    jne     height_next
+    inc     r8
+height_next:
+    inc     rcx
+    jmp     height_scan
+height_tail:
+    mov     rax, [raw_len]
+    test    rax, rax
+    jz      height_store
+    mov     dl, [raw + rax - 1]
+    cmp     dl, 10
+    je      height_store
+    inc     r8
+height_store:
+    mov     [height], r8
+
+    ; space-fill the grid, then copy the raw bytes into it
+    mov     rax, [height]
+    imul    rax, [width]
+    mov     rcx, rax
+    lea     rdi, [grid]
+    mov     al, ' '
+    rep     stosb
+
+    xor     r8, r8   ; raw index
+    xor     r9, r9   ; row
+    xor     r10, r10 ; col
+fill_loop:
+    cmp     r8, [raw_len]
+    jge     fill_done
+    mov     al, [raw + r8]
+    inc     r8
+    cmp     al, 10
+    je      fill_newline
+    cmp     al, 13
+    je      fill_loop
+    cmp     r10, [width]
+    jge     fill_loop
+    mov     rdx, r9
+    imul    rdx, [width]
+    add     rdx, r10
+    mov     [grid + rdx], al
+    inc     r10
+    jmp     fill_loop
+fill_newline:
+    inc     r9
+    xor     r10, r10
+    jmp     fill_loop
+fill_done:
+
+    ; walk the columns, carving out blocks between all-space separators
+    xor     r15, r15   ; column cursor
+block_scan:
+    cmp     r15, [width]
+    jge     blocks_done
+    mov     rdi, r15
+    call    col_is_sep
+    test    rax, rax
+    jnz     block_sep
+    mov     [blk_c0], r15
+block_extend:
+    cmp     r15, [width]
+    jge     block_end
+    mov     rdi, r15
+    call    col_is_sep
+    test    rax, rax
+    jnz     block_end
+    inc     r15
+    jmp     block_extend
+block_end:
+    mov     [blk_c1], r15
+    call    process_block
+    jmp     block_scan
+block_sep:
+    inc     r15
+    jmp     block_scan
+blocks_done:
+
+print_results:
+    mov     rcx, label1
+    call    print_string
+    mov     rax, [part1]
+    call    print_int64
+    call    print_newline
+
+    mov     rcx, label2
+    call    print_string
+    mov     rax, [part2]
+    call    print_int64
+    call    print_newline
+
+    mov     rax, SYS_EXIT
+    xor     rdi, rdi
+    syscall
+
+; col_is_sep: is every row of column RDI a space?
+;   Output: RAX = 1 if the column is a separator, else 0
+;   Clobbers: RAX, RDX, R8
+col_is_sep:
+    xor     r8, r8
+.loop:
+    cmp     r8, [height]
+    jge     .sep
+    mov     rax, r8
+    imul    rax, [width]
+    add     rax, rdi
+    movzx   edx, byte [grid + rax]
+    cmp     dl, ' '
+    jne     .not
+    inc     r8
+    jmp     .loop
+.sep:
+    mov     rax, 1
+    ret
+.not:
+    xor     rax, rax
+    ret
+
+; process_block: fold the block [blk_c0, blk_c1) for both parts.
+;   Part 1 reads each row as a number; part 2 reads each column as a number.
+;   The bottom row supplies the operator. Clobbers RAX, RCX, RDX, R8-R14.
+process_block:
+    ; find the operator on the bottom row within the block
+    mov     rax, [height]
+    dec     rax
+    imul    rax, [width]
+    mov     r11, rax   ; offset of the operator row
+    mov     qword [op], -1
+    mov     rcx, [blk_c0]
+.find_op:
+    cmp     rcx, [blk_c1]
+    jge     .op_done
+    mov     rdx, r11
+    add     rdx, rcx
+    mov     al, [grid + rdx]
+    cmp     al, '+'
+    je      .set_add
+    cmp     al, '*'
+    je      .set_mul
+    inc     rcx
+    jmp     .find_op
+.set_add:
+    mov     qword [op], 0
+    jmp     .op_done
+.set_mul:
+    mov     qword [op], 1
+.op_done:
+    cmp     qword [op], 0
+    jl      .ret   ; no operator -> not a real problem
+
+    ; part 1: one number per row
+    mov     r12, [op]
+    xor     r13, r13   ; accumulator
+    test    r12, r12
+    jz      .p1_acc
+    mov     r13, 1
+.p1_acc:
+    xor     r14, r14   ; count of numbers folded
+    xor     r10, r10   ; row
+.p1_rows:
+    mov     rax, [height]
+    dec     rax
+    cmp     r10, rax
+    jge     .p1_done
+    mov     rax, r10
+    imul    rax, [width]
+    mov     r11, rax   ; row offset
+    xor     r8, r8     ; number
+    xor     r9, r9     ; saw a digit?
+    mov     rcx, [blk_c0]
+.p1_cols:
+    cmp     rcx, [blk_c1]
+    jge     .p1_fold
+    mov     rdx, r11
+    add     rdx, rcx
+    movzx   eax, byte [grid + rdx]
+    cmp     al, '0'
+    jl      .p1_col_next
+    cmp     al, '9'
+    jg      .p1_col_next
+    sub     al, '0'
+    movzx   rax, al
+    imul    r8, r8, 10
+    add     r8, rax
+    mov     r9, 1
+.p1_col_next:
+    inc     rcx
+    jmp     .p1_cols
+.p1_fold:
+    test    r9, r9
+    jz      .p1_row_next
+    test    r12, r12
+    jnz     .p1_mul
+    add     r13, r8
+    jmp     .p1_counted
+.p1_mul:
+    imul    r13, r8
+.p1_counted:
+    inc     r14
+.p1_row_next:
+    inc     r10
+    jmp     .p1_rows
+.p1_done:
+    test    r14, r14
+    jz      .p2
+    add     [part1], r13
+
+    ; part 2: one number per column
+.p2:
+    mov     r12, [op]
+    xor     r13, r13
+    test    r12, r12
+    jz      .p2_acc
+    mov     r13, 1
+.p2_acc:
+    xor     r14, r14
+    mov     rcx, [blk_c0]   ; column
+.p2_cols:
+    cmp     rcx, [blk_c1]
+    jge     .p2_done
+    xor     r8, r8   ; number
+    xor     r9, r9   ; saw a digit?
+    xor     r10, r10 ; row
+.p2_rows:
+    mov     rax, [height]
+    dec     rax
+    cmp     r10, rax
+    jge     .p2_fold
+    mov     rax, r10
+    imul    rax, [width]
+    add     rax, rcx
+    movzx   edx, byte [grid + rax]
+    cmp     dl, '0'
+    jl      .p2_row_next
+    cmp     dl, '9'
+    jg      .p2_row_next
+    sub     dl, '0'
+    movzx   rdx, dl
+    imul    r8, r8, 10
+    add     r8, rdx
+    mov     r9, 1
+.p2_row_next:
+    inc     r10
+    jmp     .p2_rows
+.p2_fold:
+    test    r9, r9
+    jz      .p2_col_next
+    test    r12, r12
+    jnz     .p2_mul
+    add     r13, r8
+    jmp     .p2_counted
+.p2_mul:
+    imul    r13, r8
+.p2_counted:
+    inc     r14
+.p2_col_next:
+    inc     rcx
+    jmp     .p2_cols
+.p2_done:
+    test    r14, r14
+    jz      .ret
+    add     [part2], r13
+.ret:
+    ret
+
+print_newline:
+    mov     rax, SYS_WRITE
+    mov     rdi, STDOUT
+    mov     rsi, newline
+    mov     rdx, 1
+    syscall
+    ret
+
+print_int64:
+    mov     rdi, number_buffer+31
+    mov     byte [rdi], 0
+    dec     rdi
+
+    cmp     rax, 0
+    jne     .conv
+
+    mov     byte [rdi], '0'
+    jmp     .done
+.conv:
+    mov     rbx, 10
+.next:
+    xor     rdx, rdx
+    div     rbx
+    add     dl, '0'
+    mov     [rdi], dl
+    dec     rdi
+    test    rax, rax
+    jnz     .next
+
+    inc     rdi
+.done:
+    mov     rax, SYS_WRITE
+    mov     rsi, rdi
+    mov     rdi, STDOUT
+    mov     rdx, number_buffer+31
+    sub     rdx, rsi
+    syscall
+    ret
+
+print_string:
+    push    rcx
+    push    rdx
+    mov     rdx, 0
+.length:
+    cmp     byte [rcx+rdx], 0
+    je      .submit
+    inc     rdx
+    jmp     .length
+.submit:
+    mov     rax, SYS_WRITE
+    mov     rdi, STDOUT
+    mov     rsi, rcx
+    syscall
+    pop     rdx
+    pop     rcx
+    ret