# modrm19.s -- derive the complete 16-bit ModR/M effective-address table by
# EXECUTION, not from memory.  24 cases: 8 r/m values x 3 mod values.
#
# For each case: clear 0x0000..0x4FFF, store 0xBEEF through the encoding under
# test, then scan for the word and emit its offset as 2 raw bytes.
# BX=0x1000 DI=0x2000 SI=0x0030 BP=0x0040, so every candidate is distinct.
#
#   mod=00 : no displacement follows
#   mod=01 : disp8 = 0x44
#   mod=10 : disp16 = 0x1234
#
# The three "mod=11" cases are register-to-register and are not addressed here.
# Output: 24 groups of "lo hi 0x20", then 0x0A 0x0A.

.code16
.text
.globl _start
_start:
        cli
        xorw    %ax, %ax
        movw    %ax, %es
        movw    $0x1000, %bx
        movw    $0x2000, %di
        movw    $0x0030, %si
        movw    $0x0040, %bp

        # ---- mod = 00, r/m = 000..111 -------------------------------
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x00          # 00 000
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x01          # 00 001
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x02          # 00 010
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x03          # 00 011
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x04          # 00 100
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x05          # 00 101
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x06, 0x34, 0x12   # 00 110 direct
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x07          # 00 111
        call    rep_

        # ---- mod = 01, disp8 = 0x44 --------------------------------
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x40, 0x44    # 01 000
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x41, 0x44    # 01 001
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x42, 0x44    # 01 010
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x43, 0x44    # 01 011
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x44, 0x44    # 01 100
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x45, 0x44    # 01 101
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x46, 0x44    # 01 110
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x47, 0x44    # 01 111
        call    rep_

        # ---- mod = 10, disp16 = 0x1234 ------------------------------
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x80, 0x34, 0x12   # 10 000
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x81, 0x34, 0x12   # 10 001
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x82, 0x34, 0x12   # 10 010
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x83, 0x34, 0x12   # 10 011
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x84, 0x34, 0x12   # 10 100
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x85, 0x34, 0x12   # 10 101
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x86, 0x34, 0x12   # 10 110
        call    rep_
        call    clr
        movw    $0xBEEF, %ax
        .byte   0x26, 0x89, 0x87, 0x34, 0x12   # 10 111
        call    rep_

        movw    $0x3F8, %dx
        movb    $10, %al
        outb    %al, %dx
        hlt

# clr -- clear 0000:0000..0000:4FFF
clr:
        pushw   %di
        pushw   %cx
        pushw   %ax
        xorw    %ax, %ax
        movw    $0x0000, %di
        movw    $0x2800, %cx
        rep     stosw
        popw    %ax
        popw    %cx
        popw    %di
        ret

# rep_ -- emit the address of the word just stored
rep_:
        pushw   %ax
        pushw   %bx
        pushw   %cx
        pushw   %dx
        pushw   %si
        pushw   %di
        xorw    %si, %si
scan:
        cmpw    $0x3600, %si
        jae     none
        movw    %es:(%si), %dx
        cmpw    $0xBEEF, %dx
        je      found
        incw    %si
        jmp     scan
found:
        movw    %si, %ax
        call    putb
        movb    %ah, %al
        call    putb
        jmp     done
none:
        movw    $0xFF, %ax
        call    putb
        movw    $0xFF, %ax
        call    putb
done:
        movw    $0x3F8, %dx
        movb    $' ', %al
        outb    %al, %dx
        popw    %di
        popw    %si
        popw    %dx
        popw    %cx
        popw    %bx
        popw    %ax
        ret

putb:
        pushw   %dx
        movw    $0x3F8, %dx
        outb    %al, %dx
        popw    %dx
        ret