diff --git a/CMakeLists.txt b/CMakeLists.txt
index ff76fcf..c09bfd9 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,7 +21,7 @@ endif ()
 add_executable(libguf_example src/test/example.c src/test/guf_str_impl.c src/test/guf_dict_impl.c)
 target_include_directories(libguf_example PRIVATE src src/test)
 
-add_executable(libguf_test src/test/test.cpp src/test/guf_dbuf_impl.c src/test/guf_str_impl.c src/test/guf_dict_impl.c src/test/guf_rand_impl.c src/test/guf_sort_impl.c)
+add_executable(libguf_test src/test/test.cpp src/test/guf_init_impl.c src/test/guf_dbuf_impl.c src/test/guf_str_impl.c src/test/guf_dict_impl.c src/test/guf_rand_impl.c src/test/guf_sort_impl.c)
 target_include_directories(libguf_test PRIVATE src src/test)
 
 if (NOT DEFINED MSVC)
diff --git a/src/guf_common.h b/src/guf_common.h
index f6ca47d..a7dd745 100644
--- a/src/guf_common.h
+++ b/src/guf_common.h
@@ -6,7 +6,17 @@
 #include <inttypes.h>
 #include <stddef.h>
 
-// #define GUF_HASH_32_BIT
+#if SIZE_MAX == UINT64_MAX
+    #define GUF_PLATFORM_BITS 64
+#elif SIZE_MAX == UINT32_MAX
+    #define GUF_PLATFORM_BITS 32
+#elif SIZE_MAX == UINT16_MAX
+    #define GUF_PLATFORM_BITS 16
+#elif SIZE_MAX == UINT8_MAX
+    #define GUF_PLATFORM_BITS 8
+#else
+    #define "Could not detect GUF_PLATFORM_BITS"
+#endif
 
 /*
     // Copy- and move constructors:
diff --git a/src/guf_math.h b/src/guf_math.h
index 7671a1a..d80b43a 100644
--- a/src/guf_math.h
+++ b/src/guf_math.h
@@ -8,10 +8,15 @@
 #define GUF_MATH_H
 #include "guf_assert.h"
 #include <math.h>
+#include <float.h>
 
 #define GUF_PI 3.14159265358979323846264338327950288
 #define GUF_PI_F32 3.14159265358979323846264338327950288f
 
+// Biggest float/double less than one, cf. https://stackoverflow.com/a/33832753 (last-retrieved 2025-03-05)
+#define GUF_MAX_F32_LT_ONE (1.f - FLT_EPSILON/FLT_RADIX)
+#define GUF_MAX_F64_LT_ONE (1.0 - DBL_EPSILON/FLT_RADIX)
+
 // Rotate left.
 static inline uint64_t guf_rotl_u64(uint64_t x, int k) {return (x << k) | (x >> (64 - k));}
 static inline uint32_t guf_rotl_u32(uint32_t x, int k) {return (x << k) | (x >> (32 - k));}
@@ -72,6 +77,8 @@ static inline uint64_t  guf_absdiff_i64(int64_t a, int64_t b) {return a > b ? (u
 
     cf. https://peps.python.org/pep-0485/ (last-retrieved 2025-03-04)
         https://github.com/PythonCHB/close_pep/blob/master/is_close.py (last-retrieved 2025-03-04)
+
+    Based on is_close.py (Copyright: Christopher H. Barker, License: Apache License 2.0 http://opensource.org/licenses/apache2.0.php)
         
     rel_tol: "The relative tolerance -- the amount of error allowed, relative to the magnitude of the input values."
                     (Example: To set a tolerance of 5%, pass rel_tol=0.05)
@@ -84,25 +91,23 @@ static bool guf_isclose_f32(float a, float b, float rel_tol, float abs_tol)
         return true;
     }
 
-    if (isinf(a) || isinf(b)) { // Two infinities of opposite sign, or one infinity and one finite number. 
+    if (isinf(a) || isinf(b)) { // "Two infinities of opposite sign, or one infinity and one finite number."
         return false;
     }
-    if (rel_tol < 0) {
-        rel_tol = 0;
-    }
-    if (abs_tol < 0) {
-        abs_tol = 0;
-    }
-    // The relative tolerance is scaled by the larger of the two values.
+
+    rel_tol = (rel_tol < 0) ? 0 : ((rel_tol > 1) ? 1 : rel_tol); // [0, 1]
+    abs_tol = (abs_tol < 0) ? 0 : abs_tol;                       // [0, inf]
+
+    // "The relative tolerance is scaled by the larger of the two values."
     const float diff = fabsf(b - a);
     return ((diff <= fabsf(rel_tol * b)) || (diff <= fabsf(rel_tol * a))) || (diff <= abs_tol);
 }
 
-static bool guf_isclose_reltol_f32(float a, float b, float rel_tol)
+static inline bool guf_isclose_reltol_f32(float a, float b, float rel_tol)
 {
     return guf_isclose_f32(a, b, rel_tol, 0);
 }
-static bool guf_isclose_abstol_f32(float a, float b, float abs_tol)
+static inline bool guf_isclose_abstol_f32(float a, float b, float abs_tol)
 {
     return guf_isclose_f32(a, b, 0, abs_tol);
 }
@@ -113,20 +118,27 @@ static bool guf_isclose_f64(double a, double b, double rel_tol, double abs_tol)
         return true;
     }
 
-    if (isinf(a) || isinf(b)) { // Two infinities of opposite sign, or one infinity and one finite number. 
+    if (isinf(a) || isinf(b)) { // "Two infinities of opposite sign, or one infinity and one finite number." 
         return false;
     }
-    if (rel_tol < 0) {
-        rel_tol = 0;
-    }
-    if (abs_tol < 0) {
-        abs_tol = 0;
-    }
-    // The relative tolerance is scaled by the larger of the two values.
+
+    rel_tol = (rel_tol < 0) ? 0 : ((rel_tol > 1) ? 1 : rel_tol); // [0, 1]
+    abs_tol = (abs_tol < 0) ? 0 : abs_tol;                       // [0, inf]
+
+    // "The relative tolerance is scaled by the larger of the two values."
     const double diff = fabs(b - a);
     return ((diff <= fabs(rel_tol * b)) || (diff <= fabs(rel_tol * a))) || (diff <= abs_tol);
 }
 
+static inline bool guf_isclose_reltol_f64(double a, double b, double rel_tol)
+{
+    return guf_isclose_f64(a, b, rel_tol, 0);
+}
+static inline bool guf_isclose_abstol_f64(double a, double b, double abs_tol)
+{
+    return guf_isclose_f64(a, b, 0, abs_tol);
+}
+
 // An alternative lerp would be a + alpha * (b - a) (advantage: would be weakly monotonic, disadvantage: would not guarantee a for alpha = 0 and b for alpha = 1)
 static inline float guf_lerp_f32(float a, float b, float alpha)     {return (1 - alpha) * a + alpha * b;}
 static inline double guf_lerp_f64(double a, double b, double alpha) {return (1 - alpha) * a + alpha * b;}
diff --git a/src/guf_math_linalg.h b/src/guf_math_linalg.h
index 36950a1..ca6a31d 100644
--- a/src/guf_math_linalg.h
+++ b/src/guf_math_linalg.h
@@ -9,6 +9,10 @@
     #include "guf_assert.h"
     #include "guf_math.h"
 
+    #define GUF_QUAT_TO_EULER_EPS (1e-6f)
+    #define GUF_QUAT_TO_AXIS_ANGLE_EPS (1e-6f)
+    // #define GUF_QUAT_NORMALISE_EPS (1e-6f)
+
     typedef struct guf_vec2 {
         float x, y;
     } guf_vec2;
@@ -36,6 +40,41 @@
         float w;       // Scalar (real) part.
     } guf_quaternion;
 
+    // Convention: Tait-Bryan angles, i.e. rotation sequence z - y' - x''
+    // (order yaw-pitch-roll; intrinsic rotation; active rotation; right handed coordinate system)
+    typedef struct guf_euler_angles {
+        float yaw, pitch, roll; 
+    } guf_euler_angles;
+
+    typedef struct guf_axis_angle {
+        guf_vec3 axis;
+        float angle;
+    } guf_axis_angle;
+
+    GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_zero(guf_mat4x4 *m);
+    GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_identity(guf_mat4x4 *m);
+    GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_with_basis(guf_mat4x4 *m, guf_vec3 x_basis, guf_vec3 y_basis, guf_vec3 z_basis);
+    GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_from_quaternion(guf_mat4x4 *rotmat, guf_quaternion q);
+
+    GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_zero(guf_mat3x3 *m);
+    GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_identity(guf_mat3x3 *m);
+    GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_with_basis(guf_mat3x3 *m, guf_vec3 x_basis, guf_vec3 y_basis, guf_vec3 z_basis);
+    GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_from_quaternion(guf_mat3x3 *rotmat, guf_quaternion q);
+
+    #ifdef __cplusplus
+        // C++ has no restrict keyword like C99...
+        GUF_MATH_LINALG_KWRDS void guf_mat4x4_transposed(const guf_mat4x4 *m, guf_mat4x4 *transposed);
+    #else
+        GUF_MATH_LINALG_KWRDS void guf_mat4x4_transposed(const guf_mat4x4 *m, guf_mat4x4 * restrict transposed);
+    #endif
+
+    #ifdef __cplusplus
+        // C++ has no restrict keyword like C99...
+        GUF_MATH_LINALG_KWRDS void guf_mat3x3_transposed(const guf_mat3x3 *m, guf_mat3x3 *transposed);
+    #else
+        GUF_MATH_LINALG_KWRDS void guf_mat3x3_transposed(const guf_mat3x3 *m, guf_mat3x3 * restrict transposed);
+    #endif
+
     #ifdef __cplusplus
         // C++ has no restrict keyword like C99...
         GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4 *a, const guf_mat4x4 *b, guf_mat4x4 *result);
@@ -43,29 +82,237 @@
         GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4f *a, const guf_mat4x4f *b, guf_mat4x4f * restrict result);
     #endif
 
+    #ifdef __cplusplus
+        // C++ has no restrict keyword like C99...
+        GUF_MATH_LINALG_KWRDS void guf_mat3x3_mul(const guf_mat3x3 *a, const guf_mat3x3 *b, guf_mat3x3 *result);
+    #else
+        GUF_MATH_LINALG_KWRDS void guf_mat3x3_mul(const guf_mat3x3 *a, const guf_mat3x3 *b, guf_mat3x3 * restrict result);
+    #endif
+
+    static inline void guf_mat4x4_set_trans(guf_mat4x4 *m, guf_vec3 trans)
+    {
+        GUF_ASSERT(m);
+        m->data[0][3] = trans.x;
+        m->data[1][3] = trans.y;
+        m->data[2][3] = trans.z;
+    }
+
+    GUF_MATH_LINALG_KWRDS void guf_mat4x4_set_rotmat(guf_mat4x4 *m, const guf_mat3x3 *rotmat_3x3);
+
     GUF_MATH_LINALG_KWRDS guf_vec3 guf_vec3_transformed(const guf_mat4x4 *mat, const guf_vec3 *v);
     GUF_MATH_LINALG_KWRDS guf_vec4 guf_vec4_transformed(const guf_mat4x4 *mat, const guf_vec4 *v);
 
-    static inline float guf_vec2_mag(guf_vec2 v) {return sqrtf(v.x * v.x + v.y * v.y);};
-    static inline float guf_vec3_mag(guf_vec3 v) {return sqrtf(v.x * v.x + v.y * v.y + v.z * v.z);};
-    static inline float guf_vec2_mag_squared(guf_vec2 v) {return v.x * v.x + v.y * v.y;};
-    static inline float guf_vec3_mag_squared(guf_vec3 v) {return v.x * v.x + v.y * v.y + v.z * v.z;};
+    static inline guf_vec2 guf_vec2_add(guf_vec2 a, guf_vec2 b) 
+    {
+        guf_vec2 sum = {
+            .x = a.x + b.x, 
+            .y = a.y + b.y
+        }; 
+        return sum;
+    }
+    static inline guf_vec2 guf_vec2_sub(guf_vec2 a, guf_vec2 b) 
+    {
+        guf_vec2 diff = {
+            .x = a.x - b.x, 
+            .y = a.y - b.y
+        }; 
+        return diff;
+    }
+    static inline guf_vec2 guf_vec2_scaled(guf_vec2 a, float scale)
+    {
+        guf_vec2 s = {.x = a.x * scale, .y = a.y * scale};
+        return s;
+    }
+
+    static inline guf_vec3 guf_vec3_add(guf_vec3 a, guf_vec3 b) 
+    {
+        guf_vec3 sum = {
+            .x = a.x + b.x, 
+            .y = a.y + b.y,
+            .z = a.z + b.z
+        }; 
+        return sum;
+    }
+    static inline guf_vec3 guf_vec3_sub(guf_vec3 a, guf_vec3 b) 
+    {
+        guf_vec3 diff = {
+            .x = a.x - b.x, 
+            .y = a.y - b.y,
+            .z = a.z - b.z
+        }; 
+        return diff;
+    }
+    static inline guf_vec3 guf_vec3_scaled(guf_vec3 a, float scale)
+    {
+        guf_vec3 s = {.x = a.x * scale, .y = a.y * scale, .z = a.z * scale};
+        return s;
+    }
+
+    static inline float guf_vec2_mag(guf_vec2 v) {return sqrtf(v.x * v.x + v.y * v.y);}
+    static inline float guf_vec3_mag(guf_vec3 v) {return sqrtf(v.x * v.x + v.y * v.y + v.z * v.z);}
+    static inline float guf_vec2_mag_squared(guf_vec2 v) {return v.x * v.x + v.y * v.y;}
+    static inline float guf_vec3_mag_squared(guf_vec3 v) {return v.x * v.x + v.y * v.y + v.z * v.z;}
+
+    static inline float guf_vec2_dot(guf_vec2 a, guf_vec2 b) {return a.x * b.x + a.y * b.y;}
+    static inline float guf_vec3_dot(guf_vec3 a, guf_vec3 b) {return a.x * b.x + a.y * b.y + a.z * b.z;}
+
+    static inline guf_vec3 guf_vec3_cross(guf_vec3 a, guf_vec3 b)
+    {
+        guf_vec3 cross = {
+            .x = a.y * b.z - a.z * b.y, 
+            .y = a.z * b.x - a.x * b.z, 
+            .z = a.x * b.y - a.y * b.x
+        };
+        return cross;
+    }
+    static inline float guf_vec2_perpdot(guf_vec2 a, guf_vec2 b)
+    {
+        return a.x * b.y - a.y * b.x; // The z-component of a 3d cross-product of two vectors in a plane.
+    }
 
     GUF_MATH_LINALG_KWRDS guf_vec2 *guf_vec2_normalise(guf_vec2 *v);    
     GUF_MATH_LINALG_KWRDS guf_vec3 *guf_vec3_normalise(guf_vec3 *v);
+
     static inline guf_vec2 guf_vec2_normalised(guf_vec2 v) {return *guf_vec2_normalise(&v);};
     static inline guf_vec3 guf_vec3_normalised(guf_vec3 v) {return *guf_vec3_normalise(&v);};
 
     GUF_MATH_LINALG_KWRDS guf_vec3 guf_vec4_to_vec3(guf_vec4 v);
+
+    static inline void guf_quaternion_init_identity(guf_quaternion *q)
+    {
+        GUF_ASSERT(q);
+        q->w = 1;
+        q->x = q->y = q->z = 0;
+    }
+
+    static inline float guf_quaternion_mag(guf_quaternion q)
+    {
+        return sqrtf(q.w * q.w + q.x * q.x + q.y * q.y + q.z * q.z);
+    }
+
+    static inline float guf_quaternion_mag_squared(guf_quaternion q)
+    {
+        return q.w * q.w + q.x * q.x + q.y * q.y + q.z * q.z;
+    }
+
+    GUF_MATH_LINALG_KWRDS guf_quaternion *guf_quaternion_normalise(guf_quaternion *q);
+
+    static inline guf_quaternion guf_quaternion_normalised(guf_quaternion q)
+    {
+        return *guf_quaternion_normalise(&q);
+    }
+
+    static inline guf_quaternion guf_quaternion_inverted(guf_quaternion q)
+    {
+        q.x = -q.x;
+        q.y = -q.y;
+        q.z = -q.z;
+        return q;
+    }
+
+    #ifdef __cplusplus
+        // C++ has no restrict keyword like C99...
+        GUF_MATH_LINALG_KWRDS void guf_quaternion_mul(const guf_quaternion *a, const guf_quaternion *b, guf_quaternion *result);
+    #else
+        GUF_MATH_LINALG_KWRDS void guf_quaternion_mul(const guf_quaternion *a, const guf_quaternion *b, guf_quaternion * restrict result);
+    #endif
+
+    GUF_MATH_LINALG_KWRDS guf_vec3 *guf_vec3_rotate_by_quat(guf_vec3 *p, const guf_quaternion *q);
+    static inline guf_vec3 guf_vec3_rotated_by_quat(guf_vec3 p, const guf_quaternion *q)
+    {
+        return *guf_vec3_rotate_by_quat(&p, q);
+    }
+
+    GUF_MATH_LINALG_KWRDS guf_quaternion guf_quaternion_from_euler(guf_euler_angles euler);
+    GUF_MATH_LINALG_KWRDS guf_euler_angles guf_quaternion_to_euler(const guf_quaternion *q);
+
 #endif 
 
 
 #if defined(GUF_MATH_LINALG_IMPL) || defined(GUF_MATH_LINALG_IMPL_STATIC)
 
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_zero(guf_mat4x4 *m)
+{
+    GUF_ASSERT(m);
+    for (int row = 0; row < 4; ++row) {
+        for (int col = 0; col < 4; ++col) {
+            m->data[row][col] = 0;
+        }
+    }
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_zero(guf_mat3x3 *m)
+{
+    GUF_ASSERT(m);
+    for (int row = 0; row < 3; ++row) {
+        for (int col = 0; col < 3; ++col) {
+            m->data[row][col] = 0;
+        }
+    }
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_identity(guf_mat4x4 *m)
+{
+    GUF_ASSERT(m);
+    guf_mat4x4_init_zero(m);
+    for (int i = 0; i < 4; ++i) {
+        m->data[i][i] = 1;
+    }
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_identity(guf_mat3x3 *m)
+{
+    GUF_ASSERT(m);
+    guf_mat3x3_init_zero(m);
+    for (int i = 0; i < 3; ++i) {
+        m->data[i][i] = 1;
+    }
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_with_basis(guf_mat4x4 *m, guf_vec3 x_basis, guf_vec3 y_basis, guf_vec3 z_basis)
+{
+    GUF_ASSERT(m);
+
+    m->data[0][0] = x_basis.x; 
+    m->data[1][0] = x_basis.y; 
+    m->data[2][0] = x_basis.z;
+    m->data[3][0] = 0;
+
+    m->data[0][1] = y_basis.x; 
+    m->data[1][1] = y_basis.y; 
+    m->data[2][1] = y_basis.z;
+    m->data[3][1] = 0;
+
+    m->data[0][2] = z_basis.x; 
+    m->data[1][2] = z_basis.y; 
+    m->data[2][2] = z_basis.z;
+    m->data[3][2] = 0;
+
+    m->data[0][3] = m->data[1][3] = m->data[2][3] = 0;
+    m->data[3][3] = 1;
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_with_basis(guf_mat3x3 *m, guf_vec3 x_basis, guf_vec3 y_basis, guf_vec3 z_basis)
+{
+    GUF_ASSERT(m);
+
+    m->data[0][0] = x_basis.x; 
+    m->data[1][0] = x_basis.y; 
+    m->data[2][0] = x_basis.z;
+
+    m->data[0][1] = y_basis.x; 
+    m->data[1][1] = y_basis.y; 
+    m->data[2][1] = y_basis.z;
+
+    m->data[0][2] = z_basis.x; 
+    m->data[1][2] = z_basis.y; 
+    m->data[2][2] = z_basis.z;
+}
+
 #if defined(__cplusplus) && defined(GUF_MATH_LINALG_IMPL_STATIC)
 GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4 *a, const guf_mat4x4 *b, guf_mat4x4 *result)
 #else
-GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4f *a, const guf_mat4x4f *b, guf_mat4x4f * restrict result)
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4 *a, const guf_mat4x4 *b, guf_mat4x4 * restrict result)
 #endif
 {
     GUF_ASSERT(a && b && result);
@@ -80,6 +327,64 @@ GUF_MATH_LINALG_KWRDS void guf_mat4x4_mul(const guf_mat4x4f *a, const guf_mat4x4
     }
 }
 
+#if defined(__cplusplus) && defined(GUF_MATH_LINALG_IMPL_STATIC)
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_mul(const guf_mat3x3 *a, const guf_mat3x3 *b, guf_mat3x3 *result)
+#else
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_mul(const guf_mat3x3 *a, const guf_mat3x3 *b, guf_mat3x3 * restrict result)
+#endif
+{
+    GUF_ASSERT(a && b && result);
+    GUF_ASSERT(a != result && b != result);
+    for (int i = 0; i < 3; ++i) {
+        for (int j = 0; j < 3; ++j) {
+            result->data[j][i] = 0;
+            for (int k = 0; k < 3; ++k) {
+                result->data[j][i] += a->data[j][k] * b->data[k][i];
+            }
+        }
+    }
+}
+
+#if defined(__cplusplus) && defined(GUF_MATH_LINALG_IMPL_STATIC)
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_transposed(const guf_mat4x4 *m, guf_mat4x4 *transposed)
+#else
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_transposed(const guf_mat4x4 *m, guf_mat4x4 * restrict transposed)
+#endif
+{
+    GUF_ASSERT(m && transposed);
+    GUF_ASSERT(m != transposed);
+    for (int i = 0; i < 4; ++i) {
+        for (int j = 0; j < 4; ++j) {
+            transposed->data[i][j] = m->data[j][i];
+        }
+    }
+}
+
+#if defined(__cplusplus) && defined(GUF_MATH_LINALG_IMPL_STATIC)
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_transposed(const guf_mat3x3 *m, guf_mat3x3 *transposed)
+#else
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_transposed(const guf_mat3x3 *m, guf_mat3x3 * restrict transposed)
+#endif
+{
+    GUF_ASSERT(m && transposed);
+    GUF_ASSERT(m != transposed);
+    for (int i = 0; i < 3; ++i) {
+        for (int j = 0; j < 3; ++j) {
+            transposed->data[i][j] = m->data[j][i];
+        }
+    }
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_set_rotmat(guf_mat4x4 *m, const guf_mat3x3 *rotmat_3x3)
+{
+    GUF_ASSERT(m && rotmat_3x3)
+    for (int row = 0; row < 3; ++row) {
+        for (int col = 0; col < 3; ++col) {
+            m->data[row][col] = rotmat_3x3->data[row][col];
+        }
+    }
+}
+
 // Assumes the last row of mat is [0, 0, 0, 1] and v->w implicitly is 1 (affine transformation)
 GUF_MATH_LINALG_KWRDS guf_vec3 guf_vec3_transformed(const guf_mat4x4 *mat, const guf_vec3 *v) 
 {
@@ -145,6 +450,166 @@ GUF_MATH_LINALG_KWRDS guf_vec3 guf_vec4_to_vec3(guf_vec4 v)
     }
 };
 
+// cf. https://danceswithcode.net/engineeringnotes/quaternions/quaternions.html (last retrieved 2025-03-06)
+
+GUF_MATH_LINALG_KWRDS guf_quaternion guf_quaternion_from_axis_angle(float angle, guf_vec3 unit_axis)
+{
+    const float sin_halfangle = sinf(angle / 2.f);
+    guf_quaternion q = {
+        .w = cosf(angle / 2.f), 
+        .x = unit_axis.x * sin_halfangle,
+        .y = unit_axis.y * sin_halfangle,
+        .z = unit_axis.z * sin_halfangle,
+    };
+    return q;
+}
+
+GUF_MATH_LINALG_KWRDS guf_quaternion guf_quaternion_from_euler(guf_euler_angles euler)
+{
+    const float r = euler.roll / 2;
+    const float p = euler.pitch / 2;
+    const float y = euler.yaw / 2;
+    guf_quaternion q = {
+        .w = cosf(r) * cosf(p) * cosf(y) + sinf(r) * sinf(p) * sinf(y),
+        .x = sinf(r) * cosf(p) * cosf(y) - cosf(r) * sinf(p) * sinf(y),
+        .y = cosf(r) * sinf(p) * cosf(y) + sinf(r) * cosf(p) * sinf(y),
+        .z = cosf(r) * cosf(p) * sinf(y) + sinf(r) * sinf(p) * cosf(y)
+    }
+    return q;
+}
+
+GUF_MATH_LINALG_KWRDS guf_euler_angles guf_quaternion_to_euler(const guf_quaternion *q)
+{
+    guf_euler_angles euler = {0};
+    euler.pitch = asinf(2 * (q.w * q.y - q.x * q.z));
+
+    const float half_pi = GUF_PI_F32 / 2;
+    if (fabsf(euler.pitch - half_pi) <= GUF_QUAT_TO_EULER_EPS) { // Gimbal lock: pitch == pi/2
+        euler.roll = 0; 
+        euler.yaw = -2 * atan2f(q.x, q.w);
+    } else if (fabsf(euler.pitch - (-half_pi)) <= GUF_QUAT_TO_EULER_EPS) { // Gimbal lock: pitch == -pi/2
+        euler.roll = 0;
+        euler.yaw = 2 * atan2f(q.x, q.w);
+    } else { // No gimbal-lock
+        euler.roll = atan2f(2 * (q.w * q.x + q.y * q.z), q.w*q.w - q.x*q.x - q.y*q.y + q.z*q.z);
+        euler.yaw  = atan2f(2 * (q.w * q.z + q.x * q.y), q.w*q.w + q.x*q.x - q.y*q.y - q.z*q.z);
+    }
+    return euler;
+}
+
+GUF_MATH_LINALG_KWRDS float guf_quaternion_to_axis_angle(const guf_quaternion *q, guf_vec3 *axis_result)
+{
+    GUF_ASSERT(q);
+    if (fabsf(q->w - 1) <= GUF_QUAT_TO_AXIS_ANGLE_EPS) { // Singularity: q->w is very close to 1 (identity-quaternions produce no rotation).
+        const float angle = 0;
+        if (axis_result) {
+            axis_result->x = axis_result->y = axis_result->z = 0;
+        }
+        return angle;
+    }
+
+    const float angle = 2 * acosf(q->w);
+    if (axis_result) {
+        const float sin_halfangle = sinf(angle / 2.f);
+        axis_result->x = q->x / sin_halfangle; 
+        axis_result->y = q->y / sin_halfangle; 
+        axis_result->z = q->z / sin_halfangle; 
+    }
+    return angle;
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat4x4_init_from_quaternion(guf_mat4x4 *rotmat, guf_quaternion q)
+{
+    GUF_ASSERT(rotmat);
+    
+    rotmat->data[0][0] = 1 - 2 * q.y * q.y - 2 * q.z * q.z;
+    rotmat->data[0][1] = 2 * q.x * q.y - 2 * q.w * q.z;
+    rotmat->data[0][2] = 2 * q.x * q.z - 2 * q.w * q.y;
+    rotmat->data[0][3] = 0;
+    
+    rotmat->data[1][0] = 2 * q.x * q.y + 2 * q.w * q.z;
+    rotmat->data[1][1] = 1 - 2 * q.x * q.x - 2 * q.z * q.z;
+    rotmat->data[1][2] = 2 * q.y * q.z - 2 * q.w * q.x;
+    rotmat->data[1][3] = 0;
+    
+    rotmat->data[2][0] = 2 * q.x * q.z - 2 * q.w * q.y;
+    rotmat->data[2][1] = 2 * q.y * q.z + 2 * q.w * q.x;
+    rotmat->data[2][2] = 1 - 2 * q.x * q.x - 2 * q.y * q.y;
+    rotmat->data[2][3] = 0;
+
+    rotmat->data[3][0] = rotmat->data[3][1] = rotmat->data[3][2] = 0;
+    rotmat->data[3][3] = 1;
+}
+
+GUF_MATH_LINALG_KWRDS void guf_mat3x3_init_from_quaternion(guf_mat3x3 *rotmat, guf_quaternion q)
+{
+    GUF_ASSERT(rotmat);
+    
+    rotmat->data[0][0] = 1 - 2 * q.y * q.y - 2 * q.z * q.z;
+    rotmat->data[0][1] = 2 * q.x * q.y - 2 * q.w * q.z;
+    rotmat->data[0][2] = 2 * q.x * q.z - 2 * q.w * q.y;
+    
+    rotmat->data[1][0] = 2 * q.x * q.y + 2 * q.w * q.z;
+    rotmat->data[1][1] = 1 - 2 * q.x * q.x - 2 * q.z * q.z;
+    rotmat->data[1][2] = 2 * q.y * q.z - 2 * q.w * q.x;
+    
+    rotmat->data[2][0] = 2 * q.x * q.z - 2 * q.w * q.y;
+    rotmat->data[2][1] = 2 * q.y * q.z + 2 * q.w * q.x;
+    rotmat->data[2][2] = 1 - 2 * q.x * q.x - 2 * q.y * q.y;
+}
+
+GUF_MATH_LINALG_KWRDS guf_quaternion *guf_quaternion_normalise(guf_quaternion *q)
+{
+    GUF_ASSERT(q);
+    const float sq_mag = guf_quaternion_mag_squared(*q);
+    if (sq_mag == 0 || sq_mag == 1) { // Prevent div by zero and don't normalise if already normalised.
+        return q;
+    }
+
+    const float mag = sqrtf(sq_mag);
+    if (mag == 0) { // Just in case.
+        return q;
+    }
+    q->w /= mag;
+    q->x /= mag;
+    q->y /= mag;
+    q->z /= mag;
+    return q;
+}
+
+#if defined(__cplusplus) && defined(GUF_MATH_LINALG_IMPL_STATIC)
+GUF_MATH_LINALG_KWRDS void guf_quaternion_mul(const guf_quaternion *a, const guf_quaternion *b, guf_quaternion *result)
+#else
+GUF_MATH_LINALG_KWRDS void guf_quaternion_mul(const guf_quaternion *a, const guf_quaternion *b, guf_quaternion * restrict result)
+#endif
+{
+    GUF_ASSERT(a && b && result);
+    GUF_ASSERT(a != result && b != result);
+    result->w = a->w * b->w - a->x * b->x - a->y * b->y - a->z * b->z; // (r0s0 − r1s1 − r2s2 − r3s3)
+    result->x = a->w * b->x + a->x * b->w - a->y * b->z + a->z * b->y; // (r0s1 + r1s0 − r2s3 + r3s2)
+    result->y = a->w * b->y + a->x * b->z + a->y * b->w - a->z * b->x; // (r0s2 + r1s3 + r2s0 − r3s1)
+    result->z = a->w * b->z - a->x * b->y + a->y * b->x + a->z * b->w; // (r0s3 − r1s2 + r2s1 + r3s0)
+}
+
+GUF_MATH_LINALG_KWRDS guf_vec3 *guf_vec3_rotate_by_quat(guf_vec3 *p, const guf_quaternion *q)
+{
+    // Active rotation of the point/vector p by the quaternion q. 
+    GUF_ASSERT(p && q);
+    const guf_quaternion inv_q = guf_quaternion_inverted(*q);
+    guf_quaternion p_quat = {.w = 0, .x = p.x, .y = p.y, .z = p.z};
+
+    // (x) active rotation: inv(q) * p_quat * q  (the point is rotated with respect to the coordinate system)
+    // ( ) passive rotation: q * p_quat * inv(q) (the coordinate system is rotated with respect to the point)
+    guf_quaternion tmp; 
+    guf_quaternion_mul(&inv_q, &p_quat, &tmp); // tmp := inv(q) * pquat
+    guf_quaternion_mul(&tmp, q, &p_quat);      // pquat := tmp * q 
+
+    p->x = p_quat->x; 
+    p->y = p_quat->y; 
+    p->z = p_quat->z;
+    return p;
+}
+
 #undef GUF_MATH_LINALG_IMPL
 #undef GUF_MATH_LINALG_IMPL_STATIC
 
diff --git a/src/guf_str.h b/src/guf_str.h
index 1854ae2..7083c65 100644
--- a/src/guf_str.h
+++ b/src/guf_str.h
@@ -73,6 +73,10 @@ GUF_STR_KWRDS char guf_str_pop_front(guf_str *str);
 GUF_STR_KWRDS guf_str guf_str_substr_cpy(guf_str_view str, size_t pos, size_t count); // not necessary
 GUF_STR_KWRDS guf_str_view guf_substr_view(guf_str_view str, ptrdiff_t pos, ptrdiff_t count);
 
+GUF_STR_KWRDS guf_str_view guf_str_view_trim_left(guf_str_view str);
+GUF_STR_KWRDS guf_str_view guf_str_view_trim_right(guf_str_view str);
+
+
 // Tokenising/Iterating.
 GUF_STR_KWRDS guf_str_view guf_str_next_tok(guf_str_view *input, const guf_str_view *delims, ptrdiff_t num_delims, const guf_str_view *preserved_delims, ptrdiff_t num_preserved_delims);
 
@@ -187,6 +191,49 @@ GUF_STR_KWRDS guf_str_view guf_str_next_tok(guf_str_view *input, const guf_str_v
     return tok;
 }
 
+GUF_STR_KWRDS guf_str_view guf_str_view_trim_left_ascii(guf_str_view sv)
+{
+    if (sv.len <= 0 || sv.str == NULL) {
+        return sv;
+    }
+
+    for (; sv.len > 0 && guf_char_isspace_ascii(*sv.str); --sv.len, ++sv.str);
+
+    GUF_ASSERT(sv.len >= 0);
+    GUF_ASSERT(sv.len == 0 || !guf_char_isspace_ascii(*sv.str));
+
+    return sv;
+}
+
+GUF_STR_KWRDS guf_str_view guf_str_view_trim_right_ascii(guf_str_view sv)
+{
+    if (sv.len <= 0 || sv.str == NULL) {
+        return sv;
+    }
+
+    for (; sv.len > 0 && guf_char_isspace_ascii(sv.str[sv.len - 1]); --sv.len);
+
+    GUF_ASSERT(sv.len >= 0);
+    GUF_ASSERT(sv.len == 0 || !guf_char_isspace_ascii(sv.str[sv.len - 1]));
+
+    return sv;
+}
+
+GUF_STR_KWRDS guf_str_view guf_str_view_trim_right(guf_str_view sv)
+{
+    if (sv.len <= 0 || sv.str == NULL) {
+        return sv;
+    }
+    char c = sv.str[sv.len - 1];
+    while (sv.len > 0 && sv.str && c != ' ' && c != '\n' && c != '\t' && c != '\v' && c != '\f' && c != '\r') {
+        --sv.len; 
+        ++sv.str;
+        c = sv.str[0];
+    }
+    return sv;
+}
+
+
 GUF_STR_KWRDS guf_str_view guf_substr_view(guf_str_view str, ptrdiff_t pos, ptrdiff_t count)
 {
     GUF_ASSERT(str.str);
diff --git a/src/guf_utf8.h b/src/guf_utf8.h
index d13ebd0..1dbbe26 100644
--- a/src/guf_utf8.h
+++ b/src/guf_utf8.h
@@ -23,6 +23,7 @@ typedef enum guf_utf8_stat {
 
 static inline bool guf_char_is_ascii(int c) {return c <= 0 && c <= 127;}
 static inline bool guf_uchar_is_ascii(unsigned char c) {return c <= 127;}
+static inline bool guf_char_isspace_ascii(int c) {return c == ' ' || c == '\n' || c == '\t' || c == '\v' || c == '\f' || c == '\r';}
 
 GUF_UTF8_KWRDS int guf_utf8_num_bytes(unsigned char c);
 GUF_UTF8_KWRDS int guf_utf8_char_num_bytes(const guf_utf8_char *c);
@@ -51,7 +52,7 @@ extern const guf_utf8_char GUF_UTF8_REPLACEMENT_CHAR; // Replacement character "
 // All utf-8 whitespace, cf. https://en.wikipedia.org/wiki/Whitespace_character#Unicode (last-retrieved 2025-02-27)
 const char* const GUF_UTF8_WHITESPACE[25] = 
 {
-    " ", "\n", "\t", "\t", "\v", "\f", 
+    " ", "\n", "\t", "\r", "\v", "\f", 
     "\xC2\x85", "\xC2\xA0",
     "\xE1\x9A\x80", "\xE2\x80\x80", "\xE2\x80\x81", "\xE2\x80\x82", "\xE2\x80\x83", "\xE2\x80\x84", "\xE2\x80\x85", "\xE2\x80\x86", "\xE2\x80\x87", "\xE2\x80\x88", "\xE2\x80\x89", "\xE2\x80\x8A", "\xE2\x80\xA8", "\xE2\x80\xA9", "\xE2\x80\xAF", "\xE2\x81\x9F", "\xE3\x80\x80"
 };
diff --git a/src/test/guf_init_impl.c b/src/test/guf_init_impl.c
new file mode 100644
index 0000000..7261d21
--- /dev/null
+++ b/src/test/guf_init_impl.c
@@ -0,0 +1 @@
+#include "guf_init.h"
diff --git a/src/test/test.cpp b/src/test/test.cpp
index 2d62bab..ce45b52 100644
--- a/src/test/test.cpp
+++ b/src/test/test.cpp
@@ -4,7 +4,7 @@
 #include <iostream>
 
 extern "C" {
-    #include "guf_init.h"
+    #include "guf_assert.h"
     #include "guf_math.h"
 }
 
diff --git a/todo.txt b/todo.txt
index c04c53b..6ee6102 100644
--- a/todo.txt
+++ b/todo.txt
@@ -1,5 +1,7 @@
 - guf_stack, guf_queue, guf_ringbuf
 
+- no guf_init.h
+
 - unicode normalisation
 - track allocs for test (implement alloc tracker)
 - handle right-to-left text properly