signe.c
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	#include<stdio.h>
	#include<math.h>
	#include<fonction.h>
	#include<constant.h>
	#include<dimension.h>
	#include<structure.h>


	/****************************************************************/
	/* nom: signe */
	/* auteur: Jean-Paul Kneib */
	/* date: 10/02/92 */
	/* place: Toulouse */
	/****************************************************************/

	/* Return >0 if P and T->c are on the same side of the [T->a,T->b]
	* segment, otherwise <0.
	*
	* Return 0, if P or c are on the [T->a,T->b] segment.
	*
	* Global variables used :
	* - none
	*/
	double signe(const struct triplet T, const struct point P)
	{
	return(determinant(&T->a, &T->b, P)*determinant(&T->a, &T->b, &T->c));
	}

	/*********************************************************************/
	/* Return the scalar triple product (a*b).c of the 3 vectors A[x,y,1],
	* B[x,y,1], C[x,y,1].
	* If 2 of the 3 vectors are equal, colinear or form an orthogonal basis,
	* the triple product is 0.
	* This is also the determinant of the matrix
	* \| Ax Bx Cx \|
	* \| Ay By Cy \|
	* \| 1 1 1 \|
	*
	* Global variables used :
	* - none
	*/
	double determinant(const struct point *A,
	const struct point *B,
	const struct point *C)
	{
	return( B->x * C->y - B->y * C->x +
	A->x * B->y - A->y * B->x +
	A->y * C->x - A->x * C->y );
	}