glibc strtof() of FLT_MIN with 9 digits sets errno but shouldn't

[Alex Maslin]

Compile this with gcc:

#include <stdlib.h>
#include <stdio.h>
#include <float.h>
#include <errno.h>
#include <math.h>

int main(int argc, char **argv)
{
  errno = 0;
  float result = strtof(argv[1], NULL);
  printf("result==FLT_MIN %d\n", result==FLT_MIN);
  printf("errno==ERANGE %d\n", errno==ERANGE);
  printf("%.9g\n", result);
  return 0;
}

Then running it with:

> ./a.out 1.17549435e-38 # this number is FLT_MIN represented with 9 digits

gives this output:

result==FLT_MIN 1
errno==ERANGE 1
1.17549435e-38

I.e. strtof() is returning the correct result of FLT_MIN, BUT it is setting errno to ERANGE, which it should not do, errno should still be zero.

On OS X 10.15.3 / clang and on a fresh Arch Linux install / gcc, I get the correct result:

result==FLT_MIN 1
errno==ERANGE 0
1.17549435e-38

Also, back to the raspberry pi, it works with FLT_MIN rounded to 8 digits:

> ./a.out 1.1754944e-38
result==FLT_MIN 1
errno==ERANGE 0
1.17549435e-38

For information, on my raspberry pi:
> uname -a
Linux raspberrypi 5.4.51+ #1333 Mon Aug 10 16:38:02 BST 2020 armv6l GNU/Linux
> dpkg -s libc6 | grep ^Version
Version: 2.28-10+rpi1
> gcc --version
gcc (Raspbian 8.3.0-6+rpi1) 8.3.0
> cat /proc/device-tree/model
Raspberry Pi Model B Rev 12012