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explain MXCSR shenanigans in libs/pbd/fpu.cc

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git-svn-id: svn://localhost/ardour2/branches/3.0@11079 d708f5d6-7413-0410-9779-e7cbd77b26cf
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Paul Davis 2011-12-26 22:32:21 +00:00
parent 5f88b44245
commit a556546291
1 changed files with 10 additions and 0 deletions
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10
libs/pbd/fpu.cc
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@ -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