According to the C standard:
If the quotient a/b is representable, the
expression (a/b)*b + a%b shall equal a.
In your example, dividing x by -1 would make x +2147483648,
which is not representable in int32_t. May be this is
why -2147483648/-1 also exceptions out?
Nitpicking: C's % is a remainder operator, not modulus.
> On Feb 12, 2019, at 4:23 PM, Nigel Tao <[email protected]> wrote:
>
> On Mon, Feb 4, 2019 at 5:34 AM Miki Tebeka <[email protected]> wrote:
>> A bit of profiling shows that the modulo operator takes most of the time:
>
> C's modulo operator is faster, but can crash if you look at it funny.
>
> $ cat x.c
> #include <stdio.h>
>
> int main(int argc, char** argv) {
> int x = -2147483648;
> int y = -1;
> printf("x=%d\n", x);
> printf("y=%d\n", y);
> printf("m=%d\n", x % y);
> return 0;
> }
> $ gcc x.c && ./a.out
> x=-2147483648
> y=-1
> Floating point exception
>
> Compare it to the output of https://play.golang.org/p/Yj2RZmB7ZRI
>
> Yes, both the Go code and the C code will panic if y is zero. Still,
> "-2147483648 % -1" has a sensible mathematical definition (zero), and
> C fails to calculate it.
>
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