Re: [Tinycc-devel] A double-to-float conversion bug

[Vincent Lefevre]

On 2023-07-30 16:07:29 +0600, Viktor M wrote:
> Hello everyone. So today I stumbled upon this bug when doing math
> involving conversions between float and double. A minimal example:
[...]

Not really minimal. I could simplify it even further:

#include <stdio.h>

struct V {
  int x, y, z;
};

struct V vec(void)
{
  return (struct V) { 0, 0, 1 };
}

void func(float f, struct V v)
{
  printf("%f\n", f);
}

int main(void)
{
  float d = 5.0f;
  func(d, vec());
  return 0;
}

I get successively on x86_64:

-213.969727
-0.000001
-0.000000
44308718004014403453773152256.000000

Putting the 5.0f in the argument instead of d, or reducing the
struct size, or changing float to double makes the bug disappear.

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Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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