diff -r 000000000000 -r 2f259fa3e83a ode/src/quickstep.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ode/src/quickstep.cpp	Tue Feb 02 01:00:49 2010 +0200
@@ -0,0 +1,827 @@
+/*************************************************************************
+ *                                                                       *
+ * Open Dynamics Engine, Copyright (C) 2001-2003 Russell L. Smith.       *
+ * All rights reserved.  Email: russ@q12.org   Web: www.q12.org          *
+ *                                                                       *
+ * This library is free software; you can redistribute it and/or         *
+ * modify it under the terms of EITHER:                                  *
+ *   (1) The GNU Lesser General Public License as published by the Free  *
+ *       Software Foundation; either version 2.1 of the License, or (at  *
+ *       your option) any later version. The text of the GNU Lesser      *
+ *       General Public License is included with this library in the     *
+ *       file LICENSE.TXT.                                               *
+ *   (2) The BSD-style license that is included with this library in     *
+ *       the file LICENSE-BSD.TXT.                                       *
+ *                                                                       *
+ * This library is distributed in the hope that it will be useful,       *
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files    *
+ * LICENSE.TXT and LICENSE-BSD.TXT for more details.                     *
+ *                                                                       *
+ *************************************************************************/
+
+#include "object.h"
+#include "joint.h"
+#include <ode/config.h>
+#include <ode/odemath.h>
+#include <ode/rotation.h>
+#include <ode/timer.h>
+#include <ode/error.h>
+#include <ode/matrix.h>
+#include <ode/misc.h>
+#include "lcp.h"
+#include "util.h"
+
+//#define ALLOCA dALLOCA16
+
+typedef const dReal *dRealPtr;
+typedef dReal *dRealMutablePtr;
+#define dRealArray(name,n) dReal name[n];
+#define dRealAllocaArray(name,n) dReal *name = (dReal*) malloc ((n)*sizeof(dReal));
+
+//***************************************************************************
+// configuration
+
+// for the SOR method:
+// uncomment the following line to randomly reorder constraint rows
+// during the solution. depending on the situation, this can help a lot
+// or hardly at all, but it doesn't seem to hurt.
+
+#define RANDOMLY_REORDER_CONSTRAINTS 1
+
+//****************************************************************************
+// special matrix multipliers
+
+// multiply block of B matrix (q x 6) with 12 dReal per row with C vektor (q)
+static void Multiply1_12q1 (dReal *A, dReal *B, dReal *C, int q)
+{
+  int k;
+  dReal sum;
+
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[k*12],C[k]);
+  A[0] = sum;
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[1+k*12],C[k]);
+  A[1] = sum;
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[2+k*12],C[k]);
+  A[2] = sum;
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[3+k*12],C[k]);
+  A[3] = sum;
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[4+k*12],C[k]);
+  A[4] = sum;
+  sum = 0;
+  for (k=0; k<q; k++) sum += dMUL(B[5+k*12],C[k]);
+  A[5] = sum;
+}
+
+//***************************************************************************
+// testing stuff
+
+#ifdef TIMING
+#define IFTIMING(x) x
+#else
+#define IFTIMING(x) /* */
+#endif
+
+//***************************************************************************
+// various common computations involving the matrix J
+
+// compute iMJ = inv(M)*J'
+
+static void compute_invM_JT (int m, dRealMutablePtr J, dRealMutablePtr iMJ, int *jb,
+	dxBody * const *body, dRealPtr invI)
+{
+	int i,j;
+	dRealMutablePtr iMJ_ptr = iMJ;
+	dRealMutablePtr J_ptr = J;
+	for (i=0; i<m; i++) {
+		int b1 = jb[i*2];
+		int b2 = jb[i*2+1];
+		dReal k = body[b1]->invMass;
+		for (j=0; j<3; j++) iMJ_ptr[j] = dMUL(k,J_ptr[j]);
+		dMULTIPLY0_331 (iMJ_ptr + 3, invI + 12*b1, J_ptr + 3);
+		if (b2 >= 0) {
+			k = body[b2]->invMass;
+			for (j=0; j<3; j++) iMJ_ptr[j+6] = dMUL(k,J_ptr[j+6]);
+			dMULTIPLY0_331 (iMJ_ptr + 9, invI + 12*b2, J_ptr + 9);
+		}
+		J_ptr += 12;
+		iMJ_ptr += 12;
+	}
+}
+
+// compute out = J*in.
+
+static void multiply_J (int m, dRealMutablePtr J, int *jb,
+	dRealMutablePtr in, dRealMutablePtr out)
+{
+	int i,j;
+	dRealPtr J_ptr = J;
+	for (i=0; i<m; i++) {
+		int b1 = jb[i*2];
+		int b2 = jb[i*2+1];
+		dReal sum = 0;
+		dRealMutablePtr in_ptr = in + b1*6;
+		for (j=0; j<6; j++) sum += dMUL(J_ptr[j],in_ptr[j]);
+		J_ptr += 6;
+		if (b2 >= 0) {
+			in_ptr = in + b2*6;
+			for (j=0; j<6; j++) sum += dMUL(J_ptr[j],in_ptr[j]);
+		}
+		J_ptr += 6;
+		out[i] = sum;
+	}
+}
+
+
+//***************************************************************************
+// SOR-LCP method
+
+// nb is the number of bodies in the body array.
+// J is an m*12 matrix of constraint rows
+// jb is an array of first and second body numbers for each constraint row
+// invI is the global frame inverse inertia for each body (stacked 3x3 matrices)
+//
+// this returns lambda and fc (the constraint force).
+// note: fc is returned as inv(M)*J'*lambda, the constraint force is actually J'*lambda
+//
+// b, lo and hi are modified on exit
+
+
+struct IndexError {
+	dReal error;		// error to sort on
+	int findex;
+	int index;		// row index
+};
+
+
+static void SOR_LCP (int m, int nb, dRealMutablePtr J, int *jb, dxBody * const *body,
+	dRealPtr invI, dRealMutablePtr lambda, dRealMutablePtr fc, dRealMutablePtr b,
+	dRealMutablePtr lo, dRealMutablePtr hi, dRealPtr cfm, int *findex,
+	dxQuickStepParameters *qs)
+{
+	const int num_iterations = qs->num_iterations;
+	const dReal sor_w = qs->w;		// SOR over-relaxation parameter
+
+	int i,j;
+
+	dSetZero (lambda,m);
+
+	// a copy of the 'hi' vector in case findex[] is being used
+	dRealAllocaArray (hicopy,m);
+	if(hicopy == NULL) {
+		return;
+	}
+	memcpy (hicopy,hi,m*sizeof(dReal));
+
+	// precompute iMJ = inv(M)*J'
+	dRealAllocaArray (iMJ,m*12);
+	if(iMJ == NULL) {
+		free(hicopy);
+		return;
+	}
+	compute_invM_JT (m,J,iMJ,jb,body,invI);
+
+	// compute fc=(inv(M)*J')*lambda. we will incrementally maintain fc
+	// as we change lambda.
+
+	dSetZero (fc,nb*6);
+
+	// precompute 1 / diagonals of A
+	dRealAllocaArray (Ad,m);
+	if(Ad == NULL) {
+		free(hicopy);
+		free(iMJ);
+		return;
+	}
+	dRealPtr iMJ_ptr = iMJ;
+	dRealMutablePtr J_ptr = J;
+	for (i=0; i<m; i++) {
+		dReal sum = 0;
+		for (j=0; j<6; j++) sum += dMUL(iMJ_ptr[j],J_ptr[j]);
+		if (jb[i*2+1] >= 0) {
+			for (j=6; j<12; j++) sum += dMUL(iMJ_ptr[j],J_ptr[j]);
+		}
+		iMJ_ptr += 12;
+		J_ptr += 12;
+		Ad[i] = dDIV(sor_w,(sum + cfm[i]));
+	}
+
+	// scale J and b by Ad
+	J_ptr = J;
+	for (i=0; i<m; i++) {
+		for (j=0; j<12; j++) {
+			J_ptr[0] = dMUL(J_ptr[0],Ad[i]);
+			J_ptr++;
+		}
+		b[i] = dMUL(b[i],Ad[i]);
+
+		// scale Ad by CFM. N.B. this should be done last since it is used above
+		Ad[i]= dMUL(Ad[i],cfm[i]);
+	}
+
+	// order to solve constraint rows in
+	IndexError *order = (IndexError*) malloc (m*sizeof(IndexError));
+	if(order == NULL) {
+		free(hicopy);
+		free(iMJ);
+		free(Ad);
+		return;
+	}
+
+#ifndef REORDER_CONSTRAINTS
+	// make sure constraints with findex < 0 come first.
+	j=0;
+	int k=1;
+
+	// Fill the array from both ends
+	for (i=0; i<m; i++)
+		if (findex[i] < 0)
+			order[j++].index = i; // Place them at the front
+		else
+			order[m-k++].index = i; // Place them at the end
+
+
+#endif
+
+	for (int iteration=0; iteration < num_iterations; iteration++) {
+
+
+#ifdef RANDOMLY_REORDER_CONSTRAINTS
+		if ((iteration & 7) == 0) {
+			for (i=1; i<m; ++i) {
+				IndexError tmp = order[i];
+				int swapi = dRandInt(i+1);
+				order[i] = order[swapi];
+				order[swapi] = tmp;
+			}
+		}
+#endif
+
+		for (int i=0; i<m; i++) {
+			// @@@ potential optimization: we could pre-sort J and iMJ, thereby
+			//     linearizing access to those arrays. hmmm, this does not seem
+			//     like a win, but we should think carefully about our memory
+			//     access pattern.
+
+			int index = order[i].index;
+			J_ptr = J + index*12;
+			iMJ_ptr = iMJ + index*12;
+
+			// set the limits for this constraint. note that 'hicopy' is used.
+			// this is the place where the QuickStep method differs from the
+			// direct LCP solving method, since that method only performs this
+			// limit adjustment once per time step, whereas this method performs
+			// once per iteration per constraint row.
+			// the constraints are ordered so that all lambda[] values needed have
+			// already been computed.
+			if (findex[index] >= 0) {
+				hi[index] = dFabs (dMUL(hicopy[index],lambda[findex[index]]));
+				lo[index] = -hi[index];
+			}
+
+			int b1 = jb[index*2];
+			int b2 = jb[index*2+1];
+			dReal delta = b[index] - dMUL(lambda[index],Ad[index]);
+			dRealMutablePtr fc_ptr = fc + 6*b1;
+
+			// @@@ potential optimization: SIMD-ize this and the b2 >= 0 case
+			delta -=dMUL(fc_ptr[0],J_ptr[0]) + dMUL(fc_ptr[1],J_ptr[1]) +
+				dMUL(fc_ptr[2],J_ptr[2]) + dMUL(fc_ptr[3],J_ptr[3]) +
+				dMUL(fc_ptr[4],J_ptr[4]) + dMUL(fc_ptr[5],J_ptr[5]);
+			// @@@ potential optimization: handle 1-body constraints in a separate
+			//     loop to avoid the cost of test & jump?
+			if (b2 >= 0) {
+				fc_ptr = fc + 6*b2;
+				delta -=dMUL(fc_ptr[0],J_ptr[6]) + dMUL(fc_ptr[1],J_ptr[7]) +
+					dMUL(fc_ptr[2],J_ptr[8]) + dMUL(fc_ptr[3],J_ptr[9]) +
+					dMUL(fc_ptr[4],J_ptr[10]) + dMUL(fc_ptr[5],J_ptr[11]);
+			}
+
+			// compute lambda and clamp it to [lo,hi].
+			// @@@ potential optimization: does SSE have clamping instructions
+			//     to save test+jump penalties here?
+			dReal new_lambda = lambda[index] + delta;
+			if (new_lambda < lo[index]) {
+				delta = lo[index]-lambda[index];
+				lambda[index] = lo[index];
+			}
+			else if (new_lambda > hi[index]) {
+				delta = hi[index]-lambda[index];
+				lambda[index] = hi[index];
+			}
+			else {
+				lambda[index] = new_lambda;
+			}
+
+			//@@@ a trick that may or may not help
+			//dReal ramp = (1-((dReal)(iteration+1)/(dReal)num_iterations));
+			//delta *= ramp;
+
+			// update fc.
+			// @@@ potential optimization: SIMD for this and the b2 >= 0 case
+			fc_ptr = fc + 6*b1;
+			fc_ptr[0] += dMUL(delta,iMJ_ptr[0]);
+			fc_ptr[1] += dMUL(delta,iMJ_ptr[1]);
+			fc_ptr[2] += dMUL(delta,iMJ_ptr[2]);
+			fc_ptr[3] += dMUL(delta,iMJ_ptr[3]);
+			fc_ptr[4] += dMUL(delta,iMJ_ptr[4]);
+			fc_ptr[5] += dMUL(delta,iMJ_ptr[5]);
+			// @@@ potential optimization: handle 1-body constraints in a separate
+			//     loop to avoid the cost of test & jump?
+			if (b2 >= 0) {
+				fc_ptr = fc + 6*b2;
+				fc_ptr[0] += dMUL(delta,iMJ_ptr[6]);
+				fc_ptr[1] += dMUL(delta,iMJ_ptr[7]);
+				fc_ptr[2] += dMUL(delta,iMJ_ptr[8]);
+				fc_ptr[3] += dMUL(delta,iMJ_ptr[9]);
+				fc_ptr[4] += dMUL(delta,iMJ_ptr[10]);
+				fc_ptr[5] += dMUL(delta,iMJ_ptr[11]);
+			}
+		}
+	}
+	
+	free(hicopy);
+	free(iMJ);
+	free(Ad);
+	free(order);
+
+}
+
+
+void dxQuickStepper (dxWorld *world, dxBody * const *body, int nb,
+		     dxJoint * const *_joint, int nj, dReal stepsize)
+{
+	int i,j;
+	IFTIMING(dTimerStart("preprocessing");)
+
+	dReal stepsize1 = dRecip(stepsize);
+
+	// number all bodies in the body list - set their tag values
+	for (i=0; i<nb; i++) body[i]->tag = i;
+
+	// make a local copy of the joint array, because we might want to modify it.
+	// (the "dxJoint *const*" declaration says we're allowed to modify the joints
+	// but not the joint array, because the caller might need it unchanged).
+	//@@@ do we really need to do this? we'll be sorting constraint rows individually, not joints
+	dxJoint **joint = (dxJoint**) malloc (nj * sizeof(dxJoint*));
+	if(joint == NULL) {
+		return;
+	}
+	memcpy (joint,_joint,nj * sizeof(dxJoint*));
+
+	// for all bodies, compute the inertia tensor and its inverse in the global
+	// frame, and compute the rotational force and add it to the torque
+	// accumulator. I and invI are a vertical stack of 3x4 matrices, one per body.
+	//dRealAllocaArray (I,3*4*nb);	// need to remember all I's for feedback purposes only
+	dRealAllocaArray (invI,3*4*nb);
+	if( invI == NULL) {
+		free(joint);
+		return;
+	}
+	for (i=0; i<nb; i++) {
+		dMatrix3 tmp;
+
+		// compute inverse inertia tensor in global frame
+		dMULTIPLY2_333 (tmp,body[i]->invI,body[i]->posr.R);
+		dMULTIPLY0_333 (invI+i*12,body[i]->posr.R,tmp);
+	}
+
+	// add the gravity force to all bodies
+	for (i=0; i<nb; i++) {
+		if ((body[i]->flags & dxBodyNoGravity)==0) {
+			body[i]->facc[0] += dMUL( body[i]->mass.mass,world->gravity[0]);
+			body[i]->facc[1] += dMUL(body[i]->mass.mass,world->gravity[1]);
+			body[i]->facc[2] += dMUL(body[i]->mass.mass,world->gravity[2]);
+		}
+	}
+
+	// get joint information (m = total constraint dimension, nub = number of unbounded variables).
+	// joints with m=0 are inactive and are removed from the joints array
+	// entirely, so that the code that follows does not consider them.
+	//@@@ do we really need to save all the info1's
+	dxJoint::Info1 *info = (dxJoint::Info1*) malloc (nj*sizeof(dxJoint::Info1));
+	if( info == NULL) {
+		free(joint);
+		free(invI);
+		return;
+	}
+	for (i=0, j=0; j<nj; j++) {	// i=dest, j=src
+		joint[j]->vtable->getInfo1 (joint[j],info+i);
+
+		if (info[i].m > 0) {
+			joint[i] = joint[j];
+			i++;
+		}
+	}
+	nj = i;
+
+	// create the row offset array
+	int m = 0;
+	int *ofs = (int*) malloc (nj*sizeof(int));
+	if( ofs == NULL) {
+		free(joint);
+		free(invI);
+		free(info);
+		return;
+	}
+	for (i=0; i<nj; i++) {
+		ofs[i] = m;
+		m += info[i].m;
+	}
+
+	// if there are constraints, compute the constraint force
+	dRealAllocaArray (J,m*12);
+	if( J == NULL) {
+		free(joint);
+		free(invI);
+		free(info);
+		free(ofs);
+		return;
+	}
+	int *jb = (int*) malloc (m*2*sizeof(int));
+	if( jb == NULL) {
+		free(joint);
+		free(invI);
+		free(info);
+		free(ofs);
+		free(J);
+		return;
+	}
+	if (m > 0) {
+		// create a constraint equation right hand side vector `c', a constraint
+		// force mixing vector `cfm', and LCP low and high bound vectors, and an
+		// 'findex' vector.
+		dRealAllocaArray (c,m);
+		if( c == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			return;
+		}
+		dRealAllocaArray (cfm,m);
+		if( cfm == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			return;
+		}
+		dRealAllocaArray (lo,m);
+		if( lo == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			return;
+		}
+		dRealAllocaArray (hi,m);
+		if( hi == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			return;
+		}
+		int *findex = (int*) malloc (m*sizeof(int));
+		if( findex == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			return;
+		}
+		dSetZero (c,m);
+		dSetValue (cfm,m,world->global_cfm);
+		dSetValue (lo,m,-dInfinity);
+		dSetValue (hi,m, dInfinity);
+		for (i=0; i<m; i++) findex[i] = -1;
+
+		// get jacobian data from constraints. an m*12 matrix will be created
+		// to store the two jacobian blocks from each constraint. it has this
+		// format:
+		//
+		//   l1 l1 l1 a1 a1 a1 l2 l2 l2 a2 a2 a2 \    .
+		//   l1 l1 l1 a1 a1 a1 l2 l2 l2 a2 a2 a2  }-- jacobian for joint 0, body 1 and body 2 (3 rows)
+		//   l1 l1 l1 a1 a1 a1 l2 l2 l2 a2 a2 a2 /
+		//   l1 l1 l1 a1 a1 a1 l2 l2 l2 a2 a2 a2 }--- jacobian for joint 1, body 1 and body 2 (3 rows)
+		//   etc...
+		//
+		//   (lll) = linear jacobian data
+		//   (aaa) = angular jacobian data
+		//
+		IFTIMING (dTimerNow ("create J");)
+		dSetZero (J,m*12);
+		dxJoint::Info2 Jinfo;
+		Jinfo.rowskip = 12;
+		Jinfo.fps = stepsize1;
+		Jinfo.erp = world->global_erp;
+		int mfb = 0; // number of rows of Jacobian we will have to save for joint feedback
+		for (i=0; i<nj; i++) {
+			Jinfo.J1l = J + ofs[i]*12;
+			Jinfo.J1a = Jinfo.J1l + 3;
+			Jinfo.J2l = Jinfo.J1l + 6;
+			Jinfo.J2a = Jinfo.J1l + 9;
+			Jinfo.c = c + ofs[i];
+			Jinfo.cfm = cfm + ofs[i];
+			Jinfo.lo = lo + ofs[i];
+			Jinfo.hi = hi + ofs[i];
+			Jinfo.findex = findex + ofs[i];
+			joint[i]->vtable->getInfo2 (joint[i],&Jinfo);
+			// adjust returned findex values for global index numbering
+			for (j=0; j<info[i].m; j++) {
+				if (findex[ofs[i] + j] >= 0) findex[ofs[i] + j] += ofs[i];
+			}
+			if (joint[i]->feedback)
+				mfb += info[i].m;
+		}
+
+		// we need a copy of Jacobian for joint feedbacks
+		// because it gets destroyed by SOR solver
+		// instead of saving all Jacobian, we can save just rows
+		// for joints, that requested feedback (which is normaly much less)
+		dRealAllocaArray (Jcopy,mfb*12);
+		if( Jcopy == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			free(findex);
+			return;
+		}
+		if (mfb > 0) {
+			mfb = 0;
+			for (i=0; i<nj; i++)
+				if (joint[i]->feedback) {
+					memcpy(Jcopy+mfb*12, J+ofs[i]*12, info[i].m*12*sizeof(dReal));
+					mfb += info[i].m;
+				}
+		}
+
+
+		// create an array of body numbers for each joint row
+		int *jb_ptr = jb;
+		for (i=0; i<nj; i++) {
+			int b1 = (joint[i]->node[0].body) ? (joint[i]->node[0].body->tag) : -1;
+			int b2 = (joint[i]->node[1].body) ? (joint[i]->node[1].body->tag) : -1;
+			for (j=0; j<info[i].m; j++) {
+				jb_ptr[0] = b1;
+				jb_ptr[1] = b2;
+				jb_ptr += 2;
+			}
+		}
+
+
+		// compute the right hand side `rhs'
+		IFTIMING (dTimerNow ("compute rhs");)
+		dRealAllocaArray (tmp1,nb*6);
+		if( tmp1 == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			free(findex);
+			free(Jcopy);
+			return;
+		}
+		// put v/h + invM*fe into tmp1
+		for (i=0; i<nb; i++) {
+			dReal body_invMass = body[i]->invMass;
+			for (j=0; j<3; j++) tmp1[i*6+j] = dMUL(body[i]->facc[j],body_invMass) + dMUL(body[i]->lvel[j],stepsize1);
+			dMULTIPLY0_331 (tmp1 + i*6 + 3,invI + i*12,body[i]->tacc);
+			for (j=0; j<3; j++) tmp1[i*6+3+j] += dMUL(body[i]->avel[j],stepsize1);
+		}
+
+		// put J*tmp1 into rhs
+		dRealAllocaArray (rhs,m);
+		if( rhs == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			free(findex);
+			free(Jcopy);
+			free(tmp1);
+			return;
+		}
+		multiply_J (m,J,jb,tmp1,rhs);
+
+		// complete rhs
+		for (i=0; i<m; i++) rhs[i] = dMUL(c[i],stepsize1) - rhs[i];
+
+		// scale CFM
+		for (i=0; i<m; i++) cfm[i] = dMUL(cfm[i],stepsize1);
+
+		// load lambda from the value saved on the previous iteration
+		dRealAllocaArray (lambda,m);
+		if( lambda == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			free(findex);
+			free(Jcopy);
+			free(tmp1);
+			free(rhs);
+			return;
+		}
+
+		// solve the LCP problem and get lambda and invM*constraint_force
+		IFTIMING (dTimerNow ("solving LCP problem");)
+		dRealAllocaArray (cforce,nb*6);
+		if( cforce == NULL) {
+			free(joint);
+			free(invI);
+			free(info);
+			free(ofs);
+			free(J);
+			free(jb);
+			free(c);
+			free(cfm);
+			free(lo);
+			free(hi);
+			free(findex);
+			free(Jcopy);
+			free(tmp1);
+			free(rhs);
+			free(lambda);
+			return;
+		}
+		SOR_LCP (m,nb,J,jb,body,invI,lambda,cforce,rhs,lo,hi,cfm,findex,&world->qs);
+
+
+		// note that the SOR method overwrites rhs and J at this point, so
+		// they should not be used again.
+
+		// add stepsize * cforce to the body velocity
+		for (i=0; i<nb; i++) {
+			for (j=0; j<3; j++) body[i]->lvel[j] += dMUL(stepsize,cforce[i*6+j]);
+			for (j=0; j<3; j++) body[i]->avel[j] += dMUL(stepsize,cforce[i*6+3+j]);
+		}
+
+		// if joint feedback is requested, compute the constraint force.
+		// BUT: cforce is inv(M)*J'*lambda, whereas we want just J'*lambda,
+		// so we must compute M*cforce.
+		// @@@ if any joint has a feedback request we compute the entire
+		//     adjusted cforce, which is not the most efficient way to do it.
+		/*for (j=0; j<nj; j++) {
+			if (joint[j]->feedback) {
+				// compute adjusted cforce
+				for (i=0; i<nb; i++) {
+					dReal k = body[i]->mass.mass;
+					cforce [i*6+0] *= k;
+					cforce [i*6+1] *= k;
+					cforce [i*6+2] *= k;
+					dVector3 tmp;
+					dMULTIPLY0_331 (tmp, I + 12*i, cforce + i*6 + 3);
+					cforce [i*6+3] = tmp[0];
+					cforce [i*6+4] = tmp[1];
+					cforce [i*6+5] = tmp[2];
+				}
+				// compute feedback for this and all remaining joints
+				for (; j<nj; j++) {
+					dJointFeedback *fb = joint[j]->feedback;
+					if (fb) {
+						int b1 = joint[j]->node[0].body->tag;
+						memcpy (fb->f1,cforce+b1*6,3*sizeof(dReal));
+						memcpy (fb->t1,cforce+b1*6+3,3*sizeof(dReal));
+						if (joint[j]->node[1].body) {
+							int b2 = joint[j]->node[1].body->tag;
+							memcpy (fb->f2,cforce+b2*6,3*sizeof(dReal));
+							memcpy (fb->t2,cforce+b2*6+3,3*sizeof(dReal));
+						}
+					}
+				}
+			}
+		}*/
+
+		if (mfb > 0) {
+			// straightforward computation of joint constraint forces:
+			// multiply related lambdas with respective J' block for joints
+			// where feedback was requested
+			mfb = 0;
+			for (i=0; i<nj; i++) {
+				if (joint[i]->feedback) {
+					dJointFeedback *fb = joint[i]->feedback;
+					dReal data[6];
+					Multiply1_12q1 (data, Jcopy+mfb*12, lambda+ofs[i], info[i].m);
+					fb->f1[0] = data[0];
+					fb->f1[1] = data[1];
+					fb->f1[2] = data[2];
+					fb->t1[0] = data[3];
+					fb->t1[1] = data[4];
+					fb->t1[2] = data[5];
+					if (joint[i]->node[1].body)
+					{
+						Multiply1_12q1 (data, Jcopy+mfb*12+6, lambda+ofs[i], info[i].m);
+						fb->f2[0] = data[0];
+						fb->f2[1] = data[1];
+						fb->f2[2] = data[2];
+						fb->t2[0] = data[3];
+						fb->t2[1] = data[4];
+						fb->t2[2] = data[5];
+					}
+					mfb += info[i].m;
+				}
+			}
+		}
+
+		free(c);
+		free(cfm);
+		free(lo);
+		free(hi);
+		free(findex);
+		free(Jcopy);
+		free(tmp1);
+		free(rhs);
+		free(lambda);
+		free(cforce);
+		
+	}
+
+	// compute the velocity update:
+	// add stepsize * invM * fe to the body velocity
+
+	IFTIMING (dTimerNow ("compute velocity update");)
+	for (i=0; i<nb; i++) {
+		dReal body_invMass = body[i]->invMass;
+		for (j=0; j<3; j++) body[i]->lvel[j] += dMUL(stepsize,dMUL(body_invMass,body[i]->facc[j]));
+		for (j=0; j<3; j++) body[i]->tacc[j] = dMUL(body[i]->tacc[j],stepsize);
+		dMULTIPLYADD0_331 (body[i]->avel,invI + i*12,body[i]->tacc);
+	}
+
+
+	// update the position and orientation from the new linear/angular velocity
+	// (over the given timestep)
+	IFTIMING (dTimerNow ("update position");)
+	for (i=0; i<nb; i++) dxStepBody (body[i],stepsize);
+
+	IFTIMING (dTimerNow ("tidy up");)
+
+	// zero all force accumulators
+	for (i=0; i<nb; i++) {
+		dSetZero (body[i]->facc,3);
+		dSetZero (body[i]->tacc,3);
+	}
+
+	IFTIMING (dTimerEnd();)
+	IFTIMING (if (m > 0) dTimerReport (stdout,1);)
+	
+
+	free(joint);
+	free(invI);
+	free(info);
+	free(ofs);
+	free(J);
+	free(jb);
+
+}