From abedc3f573cd8986155959ab14485c031091f93a Mon Sep 17 00:00:00 2001 From: Bjørn Lindeijer Date: Wed, 15 Apr 2009 15:01:34 +0200 Subject: Make sure math functions are still inlined A function call could be quite a large overhead on top of a fast square root function. --- src/utils/mathutils.h | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) (limited to 'src/utils/mathutils.h') diff --git a/src/utils/mathutils.h b/src/utils/mathutils.h index 1b68f223..ac59ead2 100644 --- a/src/utils/mathutils.h +++ b/src/utils/mathutils.h @@ -22,10 +22,40 @@ #ifndef UTILS_MATHUTILS_H #define UTILS_MATHUTILS_H -float fastInvSqrt(float x); +/* A very fast function to calculate the approximate inverse square root of a + * floating point value and a helper function that uses it for getting the + * normal squareroot. For an explanation of the inverse squareroot function + * read: + * http://www.math.purdue.edu/~clomont/Math/Papers/2003/InvSqrt.pdf + * + * Unfortunately the original creator of this function seems to be unknown. + */ + +inline float fastInvSqrt(float x) +{ + union { int i; float x; } tmp; + float xhalf = 0.5f * x; + tmp.x = x; + tmp.i = 0x5f375a86 - (tmp.i >> 1); + x = tmp.x; + x = x * (1.5f - xhalf * x * x); + return x; +} + +inline float fastSqrt(float x) +{ + return 1.0f / fastInvSqrt(x); +} + +inline float weightedAverage(float n1, float n2, float w) +{ + if (w < 0.0f) + return n1; -float fastSqrt(float x); + if (w > 1.0f) + return n2; -float weightedAverage(float n1, float n2, float w); + return w * n2 + (1.0f - w) * n1; +} #endif // UTILS_MATHUTILS_H -- cgit v1.2.3-60-g2f50