x86 assembly UTF-16 -> UTF-8 test (GAS Syntax)

eg.c

int out2(unsigned short int t) {
    unsigned char c[3];
    unsigned char *b;
    unsigned char l = 0;
    b = c;
// 0000 0000 0xxx xxxx -> 0xxx xxxx
// 0000 0yyy yyxx xxxx -> 110y yyyy 10xx xxxx
// zzzz yyyy yyxx xxxx -> 1110 zzzz 10yy yyyy 10xx xxxx
    if ( ! (t & 0xFF80) ) {
        c[l++] = t & 0x007F;
    }
    else {
        if ( ! (t & 0xF800) ) {
            c[l++] = 0xC0 | (t & 0x07C0) >> 6;
        }
        else {
            c[l++] = 0xE0 | (t & 0xF000) >> 12;
            c[l++] = 0x80 | (t & 0x0FC0) >> 6;
        }
            c[l++] = 0x80 | t & 0x003F;
    }

    while(l--)
        printf("%c",*b++);
}

trans.S

SYS_WRITE = 4
SYS_EXIT  = 1
STDOUT = 1
RC_OK = 0

    .local ubuf
    .comm ubuf,3,1

.data
utwo:
    .short 0x0024, 0x000a
    .short 0x00A2, 0x000a
    .short 0x20AC, 0x000a
    .short 0x0000

.text
    .global _start

_start:
    xorl    %eax,%eax
    xorl    %ebx,%ebx
    xorl    %ecx,%ecx
loop:
    movw    utwo(,%ebx,2),%cx
    test    %cx,%cx
    jz     done
    call    coder
    call    putc
    inc     %ebx
    jmp     loop
    
coder:
    // in: %ecx -> w
    // out: msg -> %ecx
    // out: len -> %edx
    xorl    %edx,%edx

    test    $0xFF80,%cx
    jnz     U23
    movw    %cx,%ax
    andw    $0x007F,%ax    # 0xxx xxxx
    jmp     cdone

U23:
    test    $0xF800,%cx
    jnz     U3
    movw    %cx,%ax
    andw    $0x07C0,%ax
    sarw    $6,%ax
    orw     $0x00C0,%ax    # 110y yyxx
    movb    %al,ubuf(,%edx,1) 
    jmp     U23E

U3:
    movw    %cx,%ax
    andw    $0xF000,%ax
    sarw    $12,%ax
    orw     $0x00E0,%ax    # 1110 yyyy
    movb    %al,ubuf(,%edx,1)
    inc     %edx
    movw    %cx,%ax
    andw    $0x0FC0,%ax
    sarw    $6,%ax
    orw     $0x0080,%ax    # 10yy yyxx
    movb    %al,ubuf(,%edx,1)

U23E:
    inc     %edx
    movw    %cx,%ax
    andw    $0x003F,%ax
    orw     $0x0080,%ax    # 10xx xxxx

cdone:
    lea ubuf,%ecx
    movb    %al,(%ecx,%edx,1)
    inc     %edx
    ret

putc:
    pushl   %ebx
    movl    $STDOUT,%ebx
    movl    $SYS_WRITE,%eax
    int     $0x80
    popl    %ebx
    ret

done:
    movl    $RC_OK,%ebx
    movl    $SYS_EXIT,%eax
    int     $0x80