q_shared: better WTF constant for the Q_rsqrt trick

Author: illwieckz

src/engine/qcommon/q_shared.h

@@ -349,7 +349,9 @@ extern const quat_t   quatIdentity;
 		_mm_store_ss( &y, _mm_rsqrt_ss( _mm_load_ss( &number ) ) );
 #else
 		float x = 0.5f * number;
-		float y = Util::bit_cast<float>( 0x5f3759df - ( Util::bit_cast<uint32_t>( number ) >> 1 ) );
+		// Original value: 0x5f3759df
+		// Better value comes from: http://rrrola.wz.cz/inv_sqrt.html
+		float y = Util::bit_cast<float>( 0x5f1ffff9 - ( Util::bit_cast<uint32_t>( number ) >> 1 ) );
 		// initial iteration
 		// relative error bound after the initial iteration: 1.8 * 10^-3
 		y *= ( 1.5f - ( x * y * y ) );