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truncl: Fix setting rounding bits in FPU control word 

Mingw-w64, which is the source of this code, uses different
definitions of the rounding bits FE_TONEAREST and friends.
They immediately reflect the bit values in the FPU control word,
while on Cygwin they are shifted down to become the values 0-3.

Fix the bit computing expression to account for the difference.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2016-07-18 22:00:17 +02:00
parent 52d940e263
commit 71df3bfd51
1 changed files with 6 additions and 2 deletions
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8
winsup/cygwin/math/truncl.c
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@ -6,6 +6,10 @@
#include <fenv.h>
#include <math.h>
/* Mask and shift amount for rounding bits on x86/x86_64. */
#define FE_CW_ROUND_MASK (0x0c00)
#define FE_CW_ROUND_SHIFT (10)
long double
truncl (long double _x)
{
@ -16,8 +20,8 @@ truncl (long double _x)
unsigned short saved_cw;
unsigned short tmp_cw;
__asm__ __volatile__ ("fnstcw %0;" : "=m" (saved_cw)); /* save FPU control word */
tmp_cw = (saved_cw & ~(FE_TONEAREST | FE_DOWNWARD | FE_UPWARD | FE_TOWARDZERO))
| FE_TOWARDZERO;
tmp_cw = (saved_cw & ~FE_CW_ROUND_MASK)
| (FE_TOWARDZERO << FE_CW_ROUND_SHIFT);
__asm__ __volatile__ ("fldcw %0;" : : "m" (tmp_cw));
__asm__ __volatile__ ("frndint;" : "=t" (retval) : "0" (_x)); /* round towards zero */
__asm__ __volatile__ ("fldcw %0;" : : "m" (saved_cw) ); /* restore saved control word */