<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/89668>89668</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Fixed point integral sqrt (uksqrtui) crashes with LIBC_FAST_MATH and produces an incorrect value without LIBC_FAST_MATH
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            bug,
            libc
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
            lntue
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          PiJoules
      </td>
    </tr>
</table>

<pre>
    ```
#include <stdio.h>
#include <stdint.h>

extern "C" unsigned _Accum uksqrtui(uint32_t);

int main() {
  unsigned _Accum x = uksqrtui(65529);
  printf("%f\n", (float)x);
}
```

This will crash with `integer divide by zero` on an x86-64 linux. It looks like the main reason for this is the `FastFractType` for  `SqrtConfig<unsigned int>` is a 16-bit `unsigned fract`, so when we get to `FracType r = a * x_frac + b;`, we end up with `(0x820c * 0xfff9) // 2**16 + 0x7df8 == 0x10000` but we only retain the lower 16 bits for an unsigned fract. This is with `LIBC_FAST_MATH`.

Without `LIBC_FAST_MATH`, the error seems less clear and this will produce a value of `3.953979`. The final decimal result for either of these modes should be around `255.98632775990205`.
</pre>
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