r5sdk/r5dev/mathlib/powsse.cpp

//========= Copyright <20> 1996-2005, Valve Corporation, All rights reserved. ============//
//
// Purpose: 
//
//=====================================================================================//

#include "mathlib/ssemath.h"

// NOTE: This has to be the last file included!
#include "tier0/memdbgon.h"


fltx4 Pow_FixedPoint_Exponent_SIMD(const fltx4& x, int exponent)
{
	fltx4 rslt = Four_Ones;									// x^0=1.0
	int xp = abs(exponent);
	if (xp & 3)												// fraction present?
	{
		fltx4 sq_rt = SqrtEstSIMD(x);
		if (xp & 1)											// .25?
			rslt = SqrtEstSIMD(sq_rt);						// x^.25
		if (xp & 2)
			rslt = MulSIMD(rslt, sq_rt);
	}
	xp >>= 2;													// strip fraction
	fltx4 curpower = x;										// curpower iterates through  x,x^2,x^4,x^8,x^16...

	while (1)
	{
		if (xp & 1)
			rslt = MulSIMD(rslt, curpower);
		xp >>= 1;
		if (xp)
			curpower = MulSIMD(curpower, curpower);
		else
			break;
	}
	if (exponent < 0)
		return ReciprocalEstSaturateSIMD(rslt);				// pow(x,-b)=1/pow(x,b)
	else
		return rslt;
}




#ifndef _PS3 // these aren't fast (or correct) on the PS3
/*
 * (c) Ian Stephenson
 *
 * ian@dctsystems.co.uk
 *
 * Fast pow() reference implementation
 */


static float shift23 = (1 << 23);
static float OOshift23 = 1.0 / (1 << 23);

float FastLog2(float i)
{
	float LogBodge = 0.346607f;
	float x;
	float y;
	x = float(*(int*)&i);
	x *= OOshift23; //1/pow(2,23);
	x = x - 127;

	y = x - floorf(x);
	y = (y - y * y) * LogBodge;
	return x + y;
}
float FastPow2(float i)
{
	float PowBodge = 0.33971f;
	float x;
	float y = i - floorf(i);
	y = (y - y * y) * PowBodge;

	x = i + 127 - y;
	x *= shift23; //pow(2,23);
	*(int*)&x = (int)x;
	return x;
}
float FastPow(float a, float b)
{
	if (a <= OOshift23)
	{
		return 0.0f;
	}
	return FastPow2(b * FastLog2(a));
}
float FastPow10(float i)
{
	return FastPow2(i * 3.321928f);
}
#else
#pragma message("TODO: revisit fast logs on all PPC hardware")
#endif