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If a 32-bit integer overflows, can we use a 40-bit structure instead of a 64-bit long one?


If a 32-bit integer overflows, can we use a 40-bit structure instead of a 64-bit long one?

By : Margaret W
Date : November 19 2020, 03:59 PM
I hope this helps you . Yes, but...
It is certainly possible, but it is usually nonsensical (for any program that doesn't use billions of these numbers):
code :
#include <stdint.h> // don't want to rely on something like long long
struct bad_idea
{
    uint64_t var : 40;
};
struct using_gaps
{
    uint64_t var           : 40;
    uint64_t useful_uint16 : 16;
    uint64_t char_or_bool  : 8;  
};
Running test for array size = 1048576
what       alloc   seq(w)  seq(r)  rand(w)  rand(r)  free
-----------------------------------------------------------
uint32_t    0      2       1       35       35       1
uint64_t    0      3       3       35       35       1
bad40_t     0      5       3       35       35       1
packed40_t  0      7       4       48       49       1


Running test for array size = 16777216
what        alloc  seq(w)  seq(r)  rand(w)  rand(r)  free
-----------------------------------------------------------
uint32_t    0      38      14      560      555      8
uint64_t    0      81      22      565      554      17
bad40_t     0      85      25      565      561      16
packed40_t  0      151     75      765      774      16


Running test for array size = 134217728
what        alloc  seq(w)  seq(r)  rand(w)  rand(r)  free
-----------------------------------------------------------
uint32_t    0      312     100     4480     4441     65
uint64_t    0      648     172     4482     4490     130
bad40_t     0      682     193     4573     4492     130
packed40_t  0      1164    552     6181     6176     130


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How does the .NET VM check for integer overflows?

How does the .NET VM check for integer overflows?


By : bw-driesvc
Date : March 29 2020, 07:55 AM
wish of those help It throws only if you are within a checked context, either in the source or as a setting in the project (this is language dependent). The result of which is to out put a different IL instruction.
This is just a specific example of the general problem of arithmetic overflow and the x86 JIT implementation will doubtless insert a check of the relevant flags after any such operation with an instruction to throw an exception if the flags are set.
C++ Security Framework for Buffer Overflows, Format String Bugs and Integer Overflows

C++ Security Framework for Buffer Overflows, Format String Bugs and Integer Overflows


By : K.cantu
Date : March 29 2020, 07:55 AM
wish help you to fix your issue That's a standard feature of current Microsoft compilers, except for the format string bugs. Those aren't really C++ bugs but C bugs. C++ formatting solutions are generally typesafe.
Integer division overflows

Integer division overflows


By : user3681664
Date : March 29 2020, 07:55 AM
Hope this helps
What guarantees (in C or C++ standard) might help to devise the code?
code :
int safe_int_div(int * res, int op1, int op2) {
  if (op2 == 0) {
    return 1;
  }
  // 2's complement detection
  #if (INT_MIN != -INT_MAX) 
    if (op1 == INT_MIN && op2 == -1)  {
      return 1;
    }
  #endif
  *res = op1 / op2;
  return 0;
}
sizeof(long long) gives 8 but number overflows at 2**32

sizeof(long long) gives 8 but number overflows at 2**32


By : Rob D
Date : March 29 2020, 07:55 AM
seems to work fine You have to use the correct specifier. The "%d" specifier expects an int and you passed a long long int. According to the standard this will invoke undefined behavior. The observed behavior might be explicable but that doesn't mean it isn't rigorously undefined behavior.
Fix the code like this
code :
printf("%lld\n", prod);
printf("%zu\n", sizeof(long long)); 
3 * 1000000000 overflows as an int, but the variable is long long. Why?

3 * 1000000000 overflows as an int, but the variable is long long. Why?


By : M-B
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I have a simple c++ app that performs the following calculations , Integer constants are, by default ints.
code :
1000000000
10000000000
long long calcOne = 3 * 100000000LL;     // 3e8, essentially
long long calcTwo = 3 * 1000000000LL;    // 3e9, essentially
long long calcThree = 3 * 10000000000LL; // 3e10, essentially
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