/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
âvi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :viâ
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â Copyright 2020 Justine Alexandra Roberts Tunney                              â
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#include "dsp/core/core.h"
#include "libc/math.h"
#include "libc/str/str.h"

/**
 * Computes ðâ»Â¹ inverted 3Ã3 matrix, if it exists.
 *
 * @param ð is destination memory
 * @param ð is input matrix, which can't overlap ð
 * @param ð is |ð| the determinant scalar or 0 if degenerate
 * @return ðâ»Â¹ stored inside ð or NaNs if ð=0
 * @define ðâ»Â¹=ð such that ðÃð=ðÃð=ðâ
 * @see det3()
 */
void *inv3(double B[restrict 3][3], const double A[restrict 3][3], double d) {
  d = d ? 1 / d : NAN;
  B[0][0] = (A[1][1] * A[2][2] - A[2][1] * A[1][2]) * d;
  B[0][1] = (A[2][1] * A[0][2] - A[0][1] * A[2][2]) * d;
  B[0][2] = (A[0][1] * A[1][2] - A[1][1] * A[0][2]) * d;
  B[1][0] = (A[2][0] * A[1][2] - A[1][0] * A[2][2]) * d;
  B[1][1] = (A[0][0] * A[2][2] - A[2][0] * A[0][2]) * d;
  B[1][2] = (A[1][0] * A[0][2] - A[0][0] * A[1][2]) * d;
  B[2][0] = (A[1][0] * A[2][1] - A[2][0] * A[1][1]) * d;
  B[2][1] = (A[2][0] * A[0][1] - A[0][0] * A[2][1]) * d;
  B[2][2] = (A[0][0] * A[1][1] - A[1][0] * A[0][1]) * d;
  return B;
}
