From dc7f9bef93bffb9a35cca1e11df85039fa78f7ad Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Wed, 28 Oct 2026 23:06:08 +0100
Subject: [PATCH] bugfixes in quaternion

---
 quaternion.cc | 16 +++++++++++++++-
 quaternion.h  |  8 ++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/quaternion.cc b/quaternion.cc
index f8a4914..e6787aa 100644
--- a/quaternion.cc
+++ b/quaternion.cc
@@ -362,7 +362,7 @@ Quaternion<T> exp(const Quaternion<T> &x)
 Quaternion<T> r;
 T vnorm = sqrt(x[1]*x[1]+x[2]*x[2]+x[3]*x[3]);
 r[0] = cos(vnorm);
-vnorm = sin(vnorm)/vnorm;
+vnorm = vnorm==0 ? (T)1 : sin(vnorm)/vnorm; //limit for a real quaternion
 r[1] = x[1] * vnorm;
 r[2] = x[2] * vnorm;
 r[3] = x[3] * vnorm;
@@ -378,6 +378,13 @@ Quaternion<T> log(const Quaternion<T> &x)
 {
 Quaternion<T> r;
 T vnorm = x[1]*x[1]+x[2]*x[2]+x[3]*x[3];
+if(vnorm==0) //real quaternion; for a negative one the i axis is chosen (as for complex numbers)
+	{
+	r[0] = ::log(x[0]<0? -x[0] : x[0]);
+	r[1] = x[0]<0? (T)M_PI : (T)0;
+	r[2] = r[3] = 0;
+	return r;
+	}
 T xnorm = vnorm + x[0]*x[0];
 vnorm = sqrt(vnorm);
 xnorm = sqrt(xnorm);
@@ -395,6 +402,13 @@ Quaternion<T> pow(const Quaternion<T> &x, const T &y)
 {
 Quaternion<T> r;
 T vnorm = x[1]*x[1]+x[2]*x[2]+x[3]*x[3];
+if(vnorm==0) //real quaternion; for a negative one the i axis is chosen (as for complex numbers)
+	{
+	if(x[0]>=0) {r[0] = ::pow(x[0],y); r[1]=0;}
+	else {T a = ::pow(-x[0],y); r[0] = a*cos((T)M_PI*y); r[1] = a*sin((T)M_PI*y);}
+	r[2] = r[3] = 0;
+	return r;
+	}
 T xnorm = vnorm + x[0]*x[0];
 vnorm = sqrt(vnorm);
 xnorm = sqrt(xnorm);
diff --git a/quaternion.h b/quaternion.h
index 58bd457..24e148d 100644
--- a/quaternion.h
+++ b/quaternion.h
@@ -131,8 +131,8 @@ public:
 	//C-style IO
 	int fprintf(FILE *f, const char *format) const {return ::fprintf(f,format,q[0],q[1],q[2],q[3]);};
 	int sprintf(char *f, const char *format) const {return ::sprintf(f,format,q[0],q[1],q[2],q[3]);};
-	int fscanf(FILE *f, const char *format) const {return ::fscanf(f,format,q[0],q[1],q[2],q[3]);};
-        int sscanf(char *f, const char *format) const {return ::sscanf(f,format,q[0],q[1],q[2],q[3]);};
+	int fscanf(FILE *f, const char *format) {return ::fscanf(f,format,&q[0],&q[1],&q[2],&q[3]);};
+        int sscanf(const char *f, const char *format) {return ::sscanf(f,format,&q[0],&q[1],&q[2],&q[3]);};
 	};
 
 	
@@ -206,8 +206,8 @@ T q23= q[2]*q[3];
 if(transpose) //effectively sign change of the temporaries
 	{
 	q01 = -q01;
-	q02 = -q03;
-	q03 = -q02;
+	q02 = -q02;
+	q03 = -q03;
 	}
 a[0][1] = 2*(q12+q03);
 a[1][0] = 2*(q12-q03);