Re: 10 x 1036778084 = ??

2016-07-08 Thread Jim Wilson 

On 07/07/2016 10:07 PM, Nobby-Hirand wrote:

I have just find strange answer, 10 x 1036778084 = 1777846248??


Your target has 32-bit integers.  The value 1036778084 is close to the 
largest representable value.  Multiplying by anything larger than 2 
causes an overflow, and the result gets truncated.  Try using %x to 
print hex values to see what is wrong.  Or use long long instead of int 
to get 64-bit values.


FYI With a more recent gcc version, you can compile with 
-fsanitize=undefined and get this:


weathertop:2044$ ./a.out
tmp.c:11:5: runtime error: signed integer overflow: 10 * 1036778084 
cannot be represented in type 'int'


FYI gcc-bugs@gcc.gnu.org is used for output from our bugzilla database. 
 You shouldn't send email to this address.  You should either send 
email to gcc-help or file a bug at https://gcc.gnu.org/bugzilla/


Jim

10 x 1036778084 = ??

2016-07-07 Thread Nobby-Hirand 
I have just find strange answer, 10 x 1036778084 = 1777846248??

I'm using gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4 and gcc (GCC) 4.8.5
20150623 (Red Hat 4.8.5-4).
These are same results, 10 x 1036778084 = 1777846248

C Lang:

printf("%d \n", atoi("10367780849"));
 1777846248
Result is 1777846257, and also following source,

int y = 1036778084;
int x = 10;
int z;

z = x * y;
printf("%d x %d = %d\n", x,y,z);

10 x 1036778084 = 1777846248





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