flame.S

    .code16


start:
    /* Set the palette. */
    #define WARM    0x1010e0
    #define HOT     0xe4e0ff

    /* Switch into mode 0x13. */
    movw    $0x0013, %ax
    int     $0x10

    cld

    xorb    %al, %al
    movw    $0x3c8, %dx
    outb    %al, %dx

    incw    %dx
    xorb    %cl, %cl
1:
.macro load_palette i
    movb    $((HOT >> (\i*8)) & 0xff), %al
    subb    $((WARM >> (\i*8)) & 0xff), %al
    mulb    %cl 
    addb    $((WARM >> (\i*8)) & 0xff), %ah
    movb    %ah, %al

    mulb    %cl


    cmpw    $(30<<10), %ax
    sbbw    %bx, %bx
    shrw    $9, %ax

    andb    %bl, %al
    notb    %bl
    orb    %bl, %al


    movw    $0x3c9, %dx
    outb    %al, %dx
.endm
    /* Red */
    load_palette 0
    /* Green */
    load_palette 1
    /* Blue */
    load_palette 2

    incb %cl
    jnz  1b

2:

#define MEMORY_SECTOR 0x07e0
#define BACKUP_SECTOR 0x27e0
    movw    $BACKUP_SECTOR, %ax
    movw    %ax, %es

    xorw    %cx, %cx
    notw    %cx
    xorb    %al, %al
    rep     stosb

    movw    $MEMORY_SECTOR, %ax
    movw    %ax, %es
    movw    %ax, %ds

    xorw    %cx, %cx
    notw    %cx
    xorb    %al, %al
    rep     stosb

#define VGA_SECTOR 0xA000
    movw    $VGA_SECTOR, %ax
    movw    %ax, %fs

#define PRNG_A 1103515245
#define PRNG_C 123345
    xorl    %ebx, %ebx

2:
    xorl    %ecx, %ecx

/* Set flame base. */
1:
    movl    $PRNG_A, %eax
    mull    %ebx
    addl    $PRNG_C, %eax
    movl    %eax, %ebx

    movl    %ebx, %eax
    shrl    $24, %eax

    movb    %al, %ds:(%ecx)


    incw    %cx
    cmpw    $(320*1), %cx
    jc      1b

/* Update flame. */


    movw    $MEMORY_SECTOR, %ax
    movw    %ax, %es
    movw    $BACKUP_SECTOR, %ax
    movw    %ax, %ds


    xorw    %cx, %cx
    xorw    %si, %si
3:


    movw    %si, %bx
    addw    $4, %bx
    addw    $50, %bx
    xorw    %dx, %dx
4:
    xorw    %ax, %ax
    movb    %es:-1(%bx), %al
    addb    %es:(%bx), %al
    adcb    $0, %ah
    addb    %es:1(%bx), %al
    adcb    $0, %ah
    addb    %es:320(%bx), %al
    adcb    $0, %ah

    movw    %dx, %bp

    movw    $65400, %dx
    mulw    %dx
    movw    %dx, %ax

    movw    %bp, %dx

    shrl    $2, %ax
    movb    %al, %ds:320(%bx)

    incw    %bx
    incw    %dx
    cmpw    $(320-100), %dx
    jc      4b


    addw    $320, %si
    incw    %cx
    cmpw    $200, %cx
    jc      3b


    xorw    %si, %si

    xorw    %di, %di
    movw    $(320*200), %cx
    rep     movsb


/* Draw flame. */
    movw    $VGA_SECTOR, %ax
    movw    %ax, %es
    xorw    %di, %di
    movw    $(320*200), %si
    xorw    %dx, %dx

1:
    movw    $320, %cx
    rep     movsb

    subw    $(2*320), %si
    incw    %dx
    cmpw    $200, %dx
    jc      1b

    jmp 2b


. = start + 510
    .byte 0x55, 0xaa

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