Subversion Repositories SvarDOS

/* converts an ASCIIZ string into an unsigned short. returns 0 on success. */

int atouns(unsigned short *r, const char *s) {

  int err = 0;

  _asm {

    mov si, s

    xor ax, ax  /* general purpose register */

    xor cx, cx  /* contains the result */

    mov bx, 10  /* used as a multiplicative step */

    NEXTBYTE:

    xchg cx, ax /* move result into cx temporarily */

    lodsb  /* AL = DS:[SI++] */

    /* is AL 0? if so we're done */

    test al, al

    jz DONE

    /* validate that AL is in range '0'-'9' */

    sub al, '0'

    jc FAIL   /* neg result */

    cmp al, 9

    jg FAIL

    /* restore result into AX (CX contains the new digit) */

    xchg cx, ax

    /* multiply result by 10 and add cl */

    mul bx    /* DX AX = AX * BX(10) */

    jc FAIL   /* overflow */

    add ax, cx

    /* if CF then overflow occured (overflow part lands in DX) */

    jnc NEXTBYTE

    FAIL:

    inc [err]

    DONE: /* save result (CX) into indirect memory address r */

    mov bx, [r]

    mov [bx], cx

  }

  return(err);

}