The document discusses integer operations in C/C++ and potential errors that can occur. It proposes a SafeInt class that prevents common integer errors like overflow, underflow and division by zero at compile-time by wrapping basic integer types and checking operations. The SafeInt class aims to make integer operations safer and avoid hard to debug bugs.

1. SafeInt
안전한 정수 연산을 향해서…

2. jiniya.net

3. int a, b, c;
int d = a * b + c;

4. short len;
len = strlen(str);
warning C4244:
'=' : conversion from
'size_t' to 'short„
, possible loss of data
short len;
len = (short) strlen(str);

5. 그런 거 별 생각 없이 짠다고
뭐 큰 문제 있나요?

7. double d;
USHORT s = (USHORT) d;

9. size_t C = GetDataCount(…);
for(size_t i=0; i<C; ++i)
{
SendSecurityPacket(…);
}
int GetDataCount(…);

12. 나는
얼마나 알고 있을까?

13. char a, b, c, t, r1, r2;
a = b = c = 100;
r1 = a + b – c;
t = a + b;
r2 = t – c;
if(r1 == r2)
printf(“EQ”);
else
printf(“NEQ”);

14. int compare(INT a, USHORT b)
{
if(a > b) return 1;
else if(a < b) return -1;
else return 0;
}
printf(“%d”, compare(-1, -1));

15. int compare(INT a, UINT b)
{
if(a > b) return 1;
else if(a < b) return -1;
else return 0;
}
printf(“%d”, compare(-1, 0));

16. int a = 6;
int b = -2;
printf(“%d”, a + b);
unsigned int c = -2;
printf(“%d”, a + c);
short d = -2;
printf(“%d”, a + d);
unsigned char e = -2;
printf(“%d”, a + e);

17. int a = 6, b = -2;
printf(“%d”, a / b);
unsigned int c = -2;
printf(“%d”, a / c);
short d = -2;
printf(“%d”, a / d);
unsigned char e = -2;
printf(“%d”, a / e);

18. 제대로 배우는
C/C++ 정수 연산

19. 정수 표현 방식
• Sign Bit
• One’s complement
• Two’s complement

20. Sign Bit

21. One’s complement

22. Two’s complement

23. Two’s complement

24. Two’s complement

25. Usual Arithmetic Conversions
• If either operand is of type long double, the other operand is converted to
type long double.
• If the above condition is not met and either operand is of type double, the
other operand is converted to type double.
• If the above two conditions are not met and either operand is of type float,
the other operand is converted to type float.
• If the above three conditions are not met (none of the operands are of
floating types), then integral conversions are performed on the operands as
follows:
– If either operand is of type unsigned long, the other operand is converted to type
unsigned long.
– If the above condition is not met and either operand is of type long and the other of
type unsigned int, both operands are converted to type unsigned long.
– If the above two conditions are not met, and either operand is of type long, the other
operand is converted to type long.
– If the above three conditions are not met, and either operand is of type unsigned int,
the other operand is converted to type unsigned int.
– If none of the above conditions are met, both operands are converted to type int.

26. Usual Arithmetic Conversions
unsigned long => ULONG
long + unsigned int => ULONG
long => LONG
unsigned int => UINT
ETC => INT

27. Sign Extend
short a = -3;
int b = a;
char a = -3;
USHORT b = a;

28. Zero Extend
UCHAR a = 3;
short b = a;
USHORT a = -4;
int b = a;

29. Preserve bit pattern
UINT a = -4;
int b = a;
int a = -4;
UINT b = a;
int a = -4;
short b = a;

30. Conversion Method
• 같은 사이즈는 닥치고 Preserve.
• 큰거에서 작은거는 무조건 Preserve.
• 작은거에서 큰거는 Signed는 Sign Extend,
Unsigned는 Zero Extend.

31. Two’s Complement
int a = 6;
int b = -2;
int c = a + b;
int a = 6;
unsigned int b = -2;
int c = a + b;

32. Two’s Complement
int a = 6;
int b = -2;
int c = a / b;
int a = 6;
unsigned int b = -2;
int c = a / b;

33. 정수연산 오류

34. 정수 연산 오류
• Integer Overflow
• Sign Error
• Truncation Error

35. Integer Overflow
int compare(int a, int b)
{
if(a > b) return 1;
else if(a < b) return -1;
return 0;
}
int compare(int a, int b)
{
return a – b;
}

36. Integer Overflow
UINT sum(UINT *arr, int len)
{
UINT s = 0;
for(int i=0; i<len; ++i)
s += arr[i];
return s;
}

37. Sign Error
int size;
size = atoi(argv[1]);
char *buffer = malloc((size_t) size);

38. Sign Error
int off, len;
if(off > len – sizeof(type_name))
goto error;
int off, len;
if(off + sizeof(type_name) > len)
goto error;

39. Truncation Error
int a = USHRT_MAX + 1;
USHORT b = (USHORT) a;
short a = 3000;
char b = (char) a;

40. 왜 어려울까?
__try
{
int a = INT_MAX, b = 1;
int c = a + b;
}
__except(EXCEPTION_EXECUTE_HANDLER)
{
// ??
}

41. 왜 어려울까?
int a = INT_MAX, b = 1;
int c = a + b;
char a = INT_MAX, b = 1;
int c = a + b; INT_MAX, b = 1;
unsigned a =
int c = a = INT_MAX, b = 1;
short a + b;
int c = a + b;
long a = INT_MAX, b = 1;
int c =aa=*INT_MAX, b = 1;
char b;
int c = a * b;

42. 정수 연산 똑바로 하라고 책까지
썼는데, 사서 읽어 보는 놈이 없
눼... ㅠㅠ~
우리가 그냥 하나 만들어 주는게
좋겠어. 멍청한 애들 고생 안하
게...
그래? 근데 나 코딩 안한지 엄청
오래 됐는데. 니가 만들어. ㅋㅋ~

43. 종결자
SAFEINT

45. #include <safeint.h>
#include <limits.h>
using namespace msl::utilities;
int _tmain(int argc, _TCHAR* argv[])
{
SafeInt<int> a(UCHAR_MAX + 1);
char b = a;
return 0;
}

46. SafeInt<int> a;
int b = 1;
a = INT_MAX;
int c = a + b;
SafeInt<int> a;
a = INT_MIN;
int c = a * 2;

47. void Function(size_t len) {}
SafeInt<int> len = -2;
Function(len);

48. SafeInt<int> a = UCHAR_MAX;
short b = a;
char c = a;

49. struct SafeIntPolicyPrintNExit {
static void __stdcall
SafeIntOnOverflow() {
printf("overflown");
exit(-1);
}
static void __stdcall
SafeIntOnDivZero() {
printf("divide by zeron");
exit(-1);
}
};

50. #define _SAFEINT_DEFAULT_ERROR_POLICY
SafeIntPolicyPrintNExit
#include <safeint.h>
SafeInt<int, SafeIntPolicyPrintNExit> a;

51. try
{
SafeInt<int> a = UCHAR_MAX;
short b = a;
char c = a;
}
catch(SafeIntException &e)
{
printf("%dn", e.m_code);
}

52. enum SafeIntError
{
SafeIntNoError = 0,
SafeIntArithmeticOverflow,
SafeIntDivideByZero
};

53. SO WHAT?

54. short len;
len = strlen(str);
warning C4244:
'=' : conversion from
'size_t' to 'short„
, possible loss of data
short len;
len = (short) strlen(str);
short len;
len = SafeInt<short>(strlen(str));

55. for(int i=0; i<10; ++i) {}
for(SafeInt<int> i=0; i<10; ++i) {}

56. 감사합니다.