Re: cast of float to unsigned char bug on ARM with 3.4.5 - when was it fixed?

[John Love-Jensen <eljay@adobe.com>]

Hi Sam,

> I assume this is a know bug that got fixed in later gcc's.
> I have tried searching the gcc bug database with no luck.

It's not a GCC bug.  Your code a C bug (if I may be so presumptuous to
describe using undefined C behavior as a "bug").

Since your code is performing undefined behavior, the output of all four
examples is correct.

From "The C Programming Language" A.6.3 "The result is undefined if the
value will not fit in the space provided".  After truncation, -30 does not
fit in 0 ... 255 range (assuming your unsigned char is 8-bit), hence
undefined behavior.

One way you could fix your code to have more consistent behavior is to use
an intermediate int.

The sample code:
====================
#include <stdio.h>

int main(void)
{
  int i;
  unsigned char n1;
  float n2;

  n2 = -30.33F;
  i = (int)n2;
  n1 = (unsigned char)i;

  printf("n1: %d n2: %3.2f\n", n1, n2);

  return 0;
}
====================

As long as an int is the same bit-size and is 2's complement represented on
the platforms being compared, that should product the same output.

HTH,
--Eljay