8086 movb

8086のアセンブリ

! write(1, hello, 6);
mov ax, #1
int 7
.data1 4
.data2 hello, 6


! bx = hello;
! *(uint8_t *)bx = 'H';
mov bx, #hello
movb (bx), #'H'

! write(1, hello, 6);
mov ax, #1
int 7
.data1 4
.data2 hello, 6


! bx = hello;
! *(uint8_t *)(bx + 2) = 'L';
mov bx, #hello
movb 2(bx), #'L'

! write(1, hello, 6);
mov ax, #1
int 7
.data1 4
.data2 hello, 6


! exit(0);
mov ax, #0
int 7
.data1 1


.sect .data
hello: .ascii "hello\n"

エフシャープ

let aout = System.IO.File.ReadAllBytes "write-3.out"
let read16 (a:byte[]) b =
    (int a.[b]) ||| ((int a.[b + 1]) <<< 8)
// メモリの中の一つ一つはバイトで入れる決まりとなっている
let write16 (a:byte[]) b c =
    a.[b] <- byte c
    a.[b + 1] <- byte (c >>> 8)
let tsize = read16 aout 2
let dsize = read16 aout 4
// 16bitぶんのメモリ(に見立てた配列)を用意する
// 4bit=16進数1桁なので要素数0x10000(16bit最大数FFFF + 1)を用意する
let mem = Array.zeroCreate<byte> 0x10000
// メモリ(に見立てた配列)にテキストサイズ+データサイズ-1(=インデックス)ぶんのデータをコピーする
mem.[0 .. tsize + dsize - 1] <- aout.[16 .. 16 + tsize + dsize - 1]
let mutable ax, bx, ip = 0, 0, 0
while ip < tsize do
    match int mem.[ip], int mem.[ip + 1] with
    | 0xb8, _ ->
        ax <- read16 mem (ip + 1)
        ip <- ip + 3
    | 0xbb, _ ->
        bx <- read16 mem (ip + 1)
        ip <- ip + 3
    | 0xc7, 0x07 ->
        write16 mem bx (read16 mem (ip + 2))
        ip <- ip + 4
    | 0xc7, 0x47 ->
        write16 mem (bx + (int mem.[ip + 2])) (read16 mem (ip + 3))
        ip <- ip + 5
    | 0xc6, 0x07 ->
        mem.[bx] <- mem.[ip + 2]
        ip <- ip + 3
    | 0xc6, 0x47 ->
        mem.[bx + (int mem.[ip + 2])] <- mem.[ip + 3]
        ip <- ip + 4
    | 0xcd, 0x07 ->
        match int mem.[ip + 2] with
        | 1 ->
            exit ax
        | 4 ->
            let arg1 = read16 mem (ip + 3)
            let arg2 = read16 mem (ip + 5)
            let bytes = mem.[arg1 .. arg1 + arg2 - 1]
            printf "%s" (System.Text.Encoding.ASCII.GetString bytes)
            ip <- ip + 7
        | sc ->
            printfn "%04x: ??? syscall %d" ip sc
            exit 1
    | 0xcd, n ->
        printfn "%04x: ??? int %x" ip n
        exit 1
    | b, _ ->
        printfn "%04x: %02x ???" ip b
        exit 1

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