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#include <stdio.h>
#include <ctype.h>
#include <math.h>

#define INT_OFFSET  0x30   /* ASCII offset for integers */
#define CHAR_OFFSET 0x41   /* ASCII offset for capital letters */

#define max(x, y) (((x) >= (y)) ? (x) : (y))  

int string2int (char s[], int base)
{
    char c; 
    int i;
    int cvalue;
    int order = 0;     /* the order of the numeral in the number */
    int acc = 0;

    for (i = (size_of_number(s, base) - 1); i >= 0; i--, order++)
    {
        c = toupper(s[i]);
        if (isdigit(c))
           cvalue =  (int) c - INT_OFFSET;
        else
           /* since you know it is before the end of the integer,
              assume it is a valid letter-numeral */
           cvalue = (int) c - CHAR_OFFSET + 10;
           
        acc += pow(base, order) * cvalue;
    }
    return acc;   
}

int size_of_number(char s[], int base)
{
    int i;
    char c;
    int base_offset = max(0, base - 10);
    
    c = toupper(s[0]);
    
    for (i = 1; 
         (isdigit(c)) || (isalpha(c) && (((int) c - CHAR_OFFSET) < base_offset));
         i++)
         c = toupper(s[i]);
         
    i--;
    return i;
}


#define NUMCOUNT 6
#define NUMSIZE  3

int main()
{
    char numbers[NUMCOUNT][NUMSIZE] = {"5", "10", "24", "30", "1A", "bf"};
    int count;
    int base;
    
    puts("Original Strings:");
    for(count = 0; count < NUMCOUNT; count++)
        printf(" %s", numbers[count]);
    puts("\n");
    
    puts("Number sizes in base 16:");
    for(count = 0; count < NUMCOUNT; count++)
        printf(" %d", size_of_number(numbers[count], 16));
    puts("\n");
    
    for (base = 8; base <= 16; base++)
    {
        printf("base %d:", base);
        for(count = 0; count < NUMCOUNT; count++)
            printf(" %d", string2int(numbers[count], base));
        puts("\n");
    }
}

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 unsigned hextoint(const char * s)
{
  unsigned val, result = 0;
 
     while(*s == ' ') 
    {
      ++s;
    }  
    
     while(*s != 0 && *s != '\n')
    {
      val = *s++;
     
         if(val >= 'A' && val <= 'F') // convert to lowercase
        {
          val += 0x20;
        } 
         
         if(val >= 'a' && val <= 'f')
        {
          val -= 'a';
          val += 0x0a;
        }        
         else if(val >= '0' && val <= '9')
        {
          val -= '0';
        } 
         else
        {
          return 0;
        }         
        
      result = (result << 4) + val;
    }
 
  return result;        
}

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; yup, this is the algorithm i search for.
x = (x << 3) + (x << 1);

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org 100h

jmp   start

num1      db   3,4,5,20   ; to ease the problem, i use decimal number directly.
num2      db   6,7,8,20   ; 20 equal to termination
numTotal   dw   0      ; numTotal must contain 1023 // 3FF in the end

byte_num_add:
   xor   ax,ax
   xor   bx,bx
   byte_num_add_start:
      cmp   byte [si],20
      je   byte_num_add_return
      mov   al,[si]
      push   ax
      mov   ax,10
      mul   bx
      pop   bx
      add   bx,ax
      inc   si
      jmp   byte_num_add_start
   
   byte_num_add_return:
      ret
   
start:
   mov   si,num1         ; offset of num1
   call   byte_num_add
   mov   [numTotal],bx
   mov   si,num2         ; offset of num2
   call   byte_num_add
   mov   ax,[numTotal]
   add   bx,ax
   mov   [numTotal],bx
   jmp   finish

finish:
   mov   ah,4ch
   int 21h

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mov eax, x
next_number:
shl eax, 1
lea eax, [eax + eax*4 - 48]
add eax, [number]     ; the ascii number
cmp [number], end_character
jne next_number