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/* Copyright (c) 1994 Regents of the University of California */
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#ifndef lint
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static char SCCSid[] = "$SunId$ LBL";
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#endif
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/*
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* invmat4 - computes the inverse of mat into inverse. Returns 1
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* if there exists an inverse, 0 otherwise. It uses Gaussian Elimination
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* method.
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*/
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#include "mat4.h"
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#define ABS(x) ((x)>=0 ? (x) : -(x))
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#define SWAP(a,b,t) (t=a,a=b,b=t)
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invmat4(inverse,mat)
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MAT4 inverse, mat;
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{
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MAT4 m4tmp;
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register int i,j,k;
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register double temp;
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copymat4(m4tmp, mat);
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/* set inverse to identity */
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for (i = 0; i < 4; i++)
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for (j = 0; j < 4; j++)
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inverse[i][j] = i==j ? 1.0 : 0.0;
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for(i = 0; i < 4; i++) {
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/* Look for row with largest pivot and swap rows */
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temp = FTINY; j = -1;
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for(k = i; k < 4; k++)
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if(ABS(m4tmp[k][i]) > temp) {
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temp = ABS(m4tmp[k][i]);
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j = k;
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}
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if(j == -1) /* No replacing row -> no inverse */
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return(0);
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if (j != i)
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for(k = 0; k < 4; k++) {
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SWAP(m4tmp[i][k],m4tmp[j][k],temp);
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SWAP(inverse[i][k],inverse[j][k],temp);
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}
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temp = m4tmp[i][i];
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for(k = 0; k < 4; k++) {
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m4tmp[i][k] /= temp;
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inverse[i][k] /= temp;
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}
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for(j = 0; j < 4; j++) {
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if(j != i) {
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temp = m4tmp[j][i];
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for(k = 0; k < 4; k++) {
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m4tmp[j][k] -= m4tmp[i][k]*temp;
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inverse[j][k] -= inverse[i][k]*temp;
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}
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}
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}
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}
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return(1);
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}
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