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* [Bug middle-end/45272] New: comment about sqrt() implementation wrong: it is not from Carmack
@ 2010-08-13 0:38 ich at az2000 dot de
2010-08-13 0:44 ` [Bug middle-end/45272] " pinskia at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: ich at az2000 dot de @ 2010-08-13 0:38 UTC (permalink / raw)
To: gcc-bugs
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug middle-end/45272] comment about sqrt() implementation wrong: it is not from Carmack
2010-08-13 0:38 [Bug middle-end/45272] New: comment about sqrt() implementation wrong: it is not from Carmack ich at az2000 dot de
@ 2010-08-13 0:44 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2010-08-13 0:44 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gcc dot gnu dot org 2010-08-13 00:44 -------
Well really this code should not be using double anyways. double can produce
slight differences between targets.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45272
^ permalink raw reply [flat|nested] 2+ messages in thread
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2010-08-13 0:38 [Bug middle-end/45272] New: comment about sqrt() implementation wrong: it is not from Carmack ich at az2000 dot de
2010-08-13 0:44 ` [Bug middle-end/45272] " pinskia at gcc dot gnu dot org
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