[quake3-commits] r1990 - trunk/code/qcommon

[DONOTREPLY at icculus.org]

Author: thilo
Date: 2011-05-15 10:55:47 -0400 (Sun, 15 May 2011)
New Revision: 1990

Modified:
   trunk/code/qcommon/q_math.c
Log:
Optimise VectorNormalize functions, patch by Matt Turner


Modified: trunk/code/qcommon/q_math.c
===================================================================
--- trunk/code/qcommon/q_math.c	2011-05-15 14:49:38 UTC (rev 1989)
+++ trunk/code/qcommon/q_math.c	2011-05-15 14:55:47 UTC (rev 1990)
@@ -787,10 +787,12 @@
 	float	length, ilength;
 
 	length = v[0]*v[0] + v[1]*v[1] + v[2]*v[2];
-	length = sqrt (length);
 
 	if ( length ) {
-		ilength = 1/length;
+		/* writing it this way allows gcc to recognize that rsqrt can be used */
+		ilength = 1/(float)sqrt (length);
+		/* sqrt(length) = length * (1 / sqrt(length)) */
+		length *= ilength;
 		v[0] *= ilength;
 		v[1] *= ilength;
 		v[2] *= ilength;
@@ -803,11 +805,13 @@
 	float	length, ilength;
 
 	length = v[0]*v[0] + v[1]*v[1] + v[2]*v[2];
-	length = sqrt (length);
 
 	if (length)
 	{
-		ilength = 1/length;
+		/* writing it this way allows gcc to recognize that rsqrt can be used */
+		ilength = 1/(float)sqrt (length);
+		/* sqrt(length) = length * (1 / sqrt(length)) */
+		length *= ilength;
 		out[0] = v[0]*ilength;
 		out[1] = v[1]*ilength;
 		out[2] = v[2]*ilength;