FGFS-4.1/simgear
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Melchior FRANZ:

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This patch fixes the sound of 737, Concorde and others, if fgfs
was compiled with newer gcc versions (e.g. gcc 4.0.2). These compilers
implement the c++ standard more strictly, and thus don't guarantee
that c-style casted pointers to different data types really point
to the same address. This is only guaranteed for union members.
This commit is contained in:
ehofman 2006-02-17 09:23:40 +00:00
parent 75f817b39c
commit 606fc352aa
1 changed files with 10 additions and 8 deletions
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18
simgear/math/fastmath.hxx
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@ -51,16 +51,18 @@ void fast_BSR(float &x, register unsigned long shiftAmount);
inline float fast_log2 (float val)
{
int * const exp_ptr = reinterpret_cast <int *> (&val);
int x = *exp_ptr;
const int log_2 = ((x >> 23) & 255) - 128;
x &= ~(255 << 23);
x += 127 << 23;
*exp_ptr = x;
union {
float f;
int i;
} v;
v.f = val;
const int log_2 = ((v.i >> 23) & 255) - 128;
v.i &= ~(255 << 23);
v.i += 127 << 23;
val = ((-1.0f/3) * val + 2) * val - 2.0f/3; // (1)
v.f = ((-1.0f/3) * v.f + 2) * v.f - 2.0f/3; // (1)
return (val + log_2);
return (v.f + log_2);
}