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greg |
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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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} |
