Antonio Sanchez 5ad8b9bfe2 Make inverse 3x3 faster and avoid gcc bug.
There seems to be a gcc 4.7 bug that incorrectly flags the current
3x3 inverse as using uninitialized memory.  I'm *pretty* sure it's
a false positive, but it's hard to trigger.  The same warning
does not trigger with clang or later compiler versions.

In trying to find a work-around, this implementation turns out to be
faster anyways for static-sized matrices.

```
name                                            old cpu/op  new cpu/op  delta
BM_Inverse3x3<DynamicMatrix3T<float>>            423ns ± 2%   433ns ± 3%   +2.32%    (p=0.000 n=98+96)
BM_Inverse3x3<DynamicMatrix3T<double>>           425ns ± 2%   427ns ± 3%   +0.48%    (p=0.003 n=99+96)
BM_Inverse3x3<StaticMatrix3T<float>>            7.10ns ± 2%  0.80ns ± 1%  -88.67%  (p=0.000 n=114+112)
BM_Inverse3x3<StaticMatrix3T<double>>           7.45ns ± 2%  1.34ns ± 1%  -82.01%  (p=0.000 n=105+111)
BM_AliasedInverse3x3<DynamicMatrix3T<float>>     409ns ± 3%   419ns ± 3%   +2.40%   (p=0.000 n=100+98)
BM_AliasedInverse3x3<DynamicMatrix3T<double>>    414ns ± 3%   413ns ± 2%     ~       (p=0.322 n=98+98)
BM_AliasedInverse3x3<StaticMatrix3T<float>>     7.57ns ± 1%  0.80ns ± 1%  -89.37%  (p=0.000 n=111+114)
BM_AliasedInverse3x3<StaticMatrix3T<double>>    9.09ns ± 1%  2.58ns ±41%  -71.60%  (p=0.000 n=113+116)
```
2021-08-04 21:18:44 +00:00
2021-08-03 17:55:03 +00:00
2018-03-11 10:01:44 -04:00
2021-07-07 17:24:57 +00:00
2012-07-15 10:20:59 -04:00

Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.

For more information go to http://eigen.tuxfamily.org/.

For pull request, bug reports, and feature requests, go to https://gitlab.com/libeigen/eigen.

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