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| author | Paul Davis <paul@linuxaudiosystems.com> | 2011-12-26 22:32:21 +0000 |
|---|---|---|
| committer | Paul Davis <paul@linuxaudiosystems.com> | 2011-12-26 22:32:21 +0000 |
| commit | a556546291a86d3feae64a7a010d0756d5119f6b (patch) | |
| tree | a1d84e0cd5930447138e651a4efb695090260241 /libs/pbd/fpu.cc | |
| parent | 5f88b44245a91771dac888d2c0df0fc99aab06f7 (diff) | |
explain MXCSR shenanigans in libs/pbd/fpu.cc
git-svn-id: svn://localhost/ardour2/branches/3.0@11079 d708f5d6-7413-0410-9779-e7cbd77b26cf
Diffstat (limited to 'libs/pbd/fpu.cc')
| -rw-r--r-- | libs/pbd/fpu.cc | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/libs/pbd/fpu.cc b/libs/pbd/fpu.cc index 1018414d9b..7efc63715b 100644 --- a/libs/pbd/fpu.cc +++ b/libs/pbd/fpu.cc @@ -69,6 +69,16 @@ FPU::FPU () char* fxbuf = 0; + /* DAZ wasn't available in the first version of SSE. Since + setting a reserved bit in MXCSR causes a general protection + fault, we need to be able to check the availability of this + feature without causing problems. To do this, one needs to + set up a 512-byte area of memory to save the SSE state to, + using fxsave, and then one needs to inspect bytes 28 through + 31 for the MXCSR_MASK value. If bit 6 is set, DAZ is + supported, otherwise, it isn't. + */ + #ifdef NO_POSIX_MEMALIGN if ((fxbuf = (char *) malloc(512)) == 0) #else |