The code:
/* sqrt() implementation: based on open source QUAKE3 code (magic sqrt
implementation) by John Carmack. Returns sqrt of X. */
static double
mcf_sqrt (double x)
{
#define MAGIC_CONST1 0x1fbcf800
#define MAGIC_CONST2 0x5f3759df
union {
int intPart;
float floatPart;
} convertor, convertor2;
gcc_assert (x >= 0);
convertor.floatPart = x;
convertor2.floatPart = x;
convertor.intPart = MAGIC_CONST1 + (convertor.intPart >> 1);
convertor2.intPart = MAGIC_CONST2 - (convertor2.intPart >> 1);
return 0.5f * (convertor.floatPart + (x * convertor2.floatPart));
}
Read here:
http://en.wikipedia.org/wiki/Fast_inverse_square_root
http://www.beyond3d.com/content/articles/8/
--
Summary: comment about sqrt() implementation wrong: it is not
from Carmack
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ich at az2000 dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45272
