[sfx1999]

Pierre haven't you looked at Quake code yet? Please note that HL is based off Quake I and not Quake II. Also, make sure it is the QuakeWorld server code (unless you want client stuff).

In Quake I's mathlib.h:

/*
 Copyright (C) 1996-1997 Id Software, Inc.
 
 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; either version 2
 of the License, or (at your option) any later version.
 
 This program 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 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 
 */
 // mathlib.h
 
 typedef float vec_t;
 typedef vec_t vec3_t[3];
 typedef vec_t vec5_t[5];
 
 typedef	int	fixed4_t;
 typedef	int	fixed8_t;
 typedef	int	fixed16_t;
 
 #ifndef M_PI
 #define M_PI		3.14159265358979323846	// matches value in gcc v2 math.h
 #endif
 
 struct mplane_s;
 
 extern vec3_t vec3_origin;
 extern	int nanmask;
 
 #define	IS_NAN(x) (((*(int *)&x)&nanmask)==nanmask)
 
 #define DotProduct(x,y) (x[0]*y[0]+x[1]*y[1]+x[2]*y[2])
 #define VectorSubtract(a,b,c) {c[0]=a[0]-b[0];c[1]=a[1]-b[1];c[2]=a[2]-b[2];}
 #define VectorAdd(a,b,c) {c[0]=a[0]+b[0];c[1]=a[1]+b[1];c[2]=a[2]+b[2];}
 #define VectorCopy(a,b) {b[0]=a[0];b[1]=a[1];b[2]=a[2];}
 
 void VectorMA (vec3_t veca, float scale, vec3_t vecb, vec3_t vecc);
 
 vec_t _DotProduct (vec3_t v1, vec3_t v2);
 void _VectorSubtract (vec3_t veca, vec3_t vecb, vec3_t out);
 void _VectorAdd (vec3_t veca, vec3_t vecb, vec3_t out);
 void _VectorCopy (vec3_t in, vec3_t out);
 
 int VectorCompare (vec3_t v1, vec3_t v2);
 vec_t Length (vec3_t v);
 void CrossProduct (vec3_t v1, vec3_t v2, vec3_t cross);
 float VectorNormalize (vec3_t v);		// returns vector length
 void VectorInverse (vec3_t v);
 void VectorScale (vec3_t in, vec_t scale, vec3_t out);
 int Q_log2(int val);
 
 void R_ConcatRotations (float in1[3][3], float in2[3][3], float out[3][3]);
 void R_ConcatTransforms (float in1[3][4], float in2[3][4], float out[3][4]);
 
 void FloorDivMod (double numer, double denom, int *quotient,
 		int *rem);
 fixed16_t Invert24To16(fixed16_t val);
 fixed16_t Mul16_30(fixed16_t multiplier, fixed16_t multiplicand);
 int GreatestCommonDivisor (int i1, int i2);
 
 void AngleVectors (vec3_t angles, vec3_t forward, vec3_t right, vec3_t up);
 int BoxOnPlaneSide (vec3_t emins, vec3_t emaxs, struct mplane_s *plane);
 float	anglemod(float a);
 
 void RotatePointAroundVector( vec3_t dst, const vec3_t dir, const vec3_t point, float degrees );
 
 
 #define BOX_ON_PLANE_SIDE(emins, emaxs, p)	\
 	(((p)->type < 3)?    		    		\
 	(	    		    		    		\
 		((p)->dist <= (emins)[(p)->type])?	\
 		    1		    		    		\
 		:    		    		    		\
 		(    		    		    		\
 			((p)->dist >= (emaxs)[(p)->type])?\
 		    	2	    		    		\
 		    :		    		    		\
 		    	3	    		    		\
 		)    		    		    		\
 	)	    		    		    		\
 	:	    		    		    		\
 		BoxOnPlaneSide( (emins), (emaxs), (p)))