I have found some alternative code to set the floating-point precision:
unsigned int fpu_cw;
_controlfp_s(&fpu_cw, _PC_53, _MCW_PC);
Instead of _PC_53 I have also tried _PC_24 and _PC_64. But this didn't help.
The two threads still behave differently.
-----Ursprüngliche Nachricht-----
Von: Burkhardt, Glenn B UTAS [mailto:glenn.burkha...@utas.utc.com]
Gesendet: Dienstag, 1. März 2016 17:42
An: mingw-w64-public@lists.sourceforge.net
Betreff: [Mingw-w64-public] Floating-Point Operations Not Deterministic When
Excecuted Asynchronously
You're probably running into the fact that Intel processors have floating point
registers with 80 bits, and when optimization is turned on, operations are done
in registers and not truncated as they are when the values are stored to memory.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323 Notice the number of
duplicated reports - it's a surprise to a lot of people.
There are ways to set the precision used by the FPU, e.g.,
#include "fpu_control.h"
fpu_control_t cw;
_FPU_GETCW(cw);
cw &= ~_FPU_EXTENDED;
cw |= _FPU_DOUBLE;
_FPU_SETCW(cw);
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