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[Bug 2120875] Re: gl_vec.cc fails to compile with C23 with "error: call of overloaded ‘rsqrt(double)’ is ambiguous"

To: debcrafters-packages@xxxxxxxxxxxxxxxxxxx
From: Simon Chopin <2120875@xxxxxxxxxxxxxxxxxx>
Date: Wed, 20 Aug 2025 14:57:23 -0000
Reply-to: Bug 2120875 <2120875@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx

Marking this as affecting glibc, for clarity.

** Also affects: glibc (Ubuntu)
   Importance: Undecided
       Status: New

** Tags added: update-excuse

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https://bugs.launchpad.net/bugs/2120875

Title:
  gl_vec.cc fails to compile with C23 with "error: call of overloaded
  ‘rsqrt(double)’ is ambiguous"

Status in glibc package in Ubuntu:
  New
Status in openmsx package in Ubuntu:
  In Progress

Bug description:
  Version 20.0+dfsg-1.2

  log snippet:
  ```
  ...
  1653s In file included from src/unittest/gl_vec.cc:1:
  1653s src/unittest/gl_vec.cc: In function ‘void ____C_A_T_C_H____T_E_S_T____0()’:
  1653s src/unittest/gl_vec.cc:24:20: error: call of overloaded ‘rsqrt(double)’ is ambiguous
  1653s    24 |         CHECK(rsqrt(16.0 ) == 0.25 );
  1653s       |               ~~~~~^~~~~~~
  1653s src/unittest/gl_vec.cc:24:20: note: there are 3 candidates
  1653s In file included from /usr/include/features.h:523,
  1653s                  from /usr/include/x86_64-linux-gnu/c++/15/bits/os_defines.h:39,
  1653s                  from /usr/include/x86_64-linux-gnu/c++/15/bits/c++config.h:727,
  1653s                  from /usr/include/c++/15/cstddef:51,
  1653s                  from Contrib/catch2/catch.hpp:328:
  1653s /usr/include/x86_64-linux-gnu/bits/mathcalls.h:206:1: note: candidate 1: ‘double rsqrt(double)’
  1653s   206 | __MATHCALL (rsqrt,, (_Mdouble_ __x));
  1653s       | ^~~~~~~~~~
  1653s In file included from src/unittest/gl_vec.cc:2:
  1653s src/video/gl_vec.hh:196:28: note: candidate 2: ‘float gl::rsqrt(float)’
  1653s   196 | [[nodiscard]] inline float rsqrt(float x)
  1653s       |                            ^~~~~
  1653s src/video/gl_vec.hh:200:29: note: candidate 3: ‘double gl::rsqrt(double)’
  1653s   200 | [[nodiscard]] inline double rsqrt(double x)
  1653s       |                             ^~~~~
  ...
  ```

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