Use _BitScanForward and _BitScanReverse so x86 builds still compile

[dlrdave]

Summary of Changes

Use _BitScanForward and _BitScanReverse so x86 builds still compile

More precisely, avoid using _BitScanForward64 and _BitScanReverse64 since they do not exist in the x86 compiler intrinsics.

https://learn.microsoft.com/en-us/cpp/intrinsics/bitscanforward-bitscanforward64?view=msvc-170

Avoids these compiler errors:
CGAL\include\CGAL/cpp_float.h(30): error C3861: '_BitScanForward64': identifier not found
CGAL\include\CGAL/cpp_float.h(42): error C3861: '_BitScanReverse64': identifier not found

Release Management

• Affected package(s): Number_types
• Issue(s) solved (if any): compiler errors encountered on Windows x86 builds
• License and copyright ownership: unchanged

[lrineau]

Hi @dlrdave. Do you still have Windows 32 bits builds of products using CGAL?

Is that for Neocis?

[dlrdave]

Hi @dlrdave. Do you still have Windows 32 bits builds of products using CGAL?

Is that for Neocis?

Yes, this is a patch we are using at Neocis to keep 32 bit builds working. We are not actively using CGAL in any 32-bit products, but this patch is easier for us than the amount of work it would take to exclude single packages from our 32-bit library building pipeline.

[lrineau]

Can you please have a look at the PR #7635 and in particular that comment #7635 (comment)?

I am surprised that you have build issues with Windows x86, because PR #7635 disabled the support of Boost MP with that platform.

[sloriot]

Can you please have a look at the PR #7635 and in particular that comment #7635 (comment)?

I am surprised that you have build issues with Windows x86, because PR #7635 disabled the support of Boost MP with that platform.

It's not yet released, it will be part of 5.6.1

[dlrdave]

It's not yet released, it will be part of 5.6.1

:-)

OK, thanks. You can reject this PR then, and we will pick up 5.6.1 when it comes out, or hopefully even update to 6 in the near future instead.

[dlrdave]

Closing this PR, since an equivalent fix is already slated to be included in the upcoming 5.6.1 release.

[lrineau]

Closing this PR, since an equivalent fix is already slated to be included in the upcoming 5.6.1 release.

Actually, that is not completely equivalent:

• this PR Use _BitScanForward and _BitScanReverse so x86 builds still compile #7896 tries to fix our Boost MP support with Windows x86,
• the PR patch to support PowerPC and Windows 32 bits #7635 disabled Boost MP support with Windows x86.

That is quite different. If Neocis still use Windows x86 builds, then maybe the CGAL project should start again to test on that platform. Please tell us.

[dlrdave]

If Neocis still use Windows x86 builds, then maybe the CGAL project should start again to test on that platform. Please tell us.

I would rather do the work of excluding CGAL from our x86 pipeline than impose the testing burden of such an old platform on the CGAL project. Thanks, but we can patch for now, and exclude in a little while. We only really need CGAL support on 64-bit platforms.