revert build to older cython

ctpfrec/cy_double.pxi

@@ -3,7 +3,13 @@ from scipy.linalg.cython_blas cimport ddot
 from hpfrec import cython_loops_double as cython_loops
 import ctypes
 
-from libc.math cimport log, exp, HUGE_VAL, HUGE_VALL
+# TODO: once issues with newer cython are sorted out, should cimport as below:
+# from libc.math cimport log, exp, HUGE_VAL, HUGE_VALL
+cdef extern from "<math.h>":
+    double log(double x) nogil
+    double exp(double x) nogil
+    const double HUGE_VAL
+    const long double HUGE_VALL
 
 c_real_t = ctypes.c_double
 ctypedef double real_t

ctpfrec/cy_float.pxi

@@ -6,7 +6,16 @@ from scipy.special.cython_special cimport psi, gamma
 from hpfrec import cython_loops_float as cython_loops
 import ctypes
 
-from libc.math cimport log, exp, logf, expf, HUGE_VALF, HUGE_VAL, HUGE_VALL
+# TODO: once issues with newer cython are sorted out, should cimport as below:
+# from libc.math cimport log, exp, logf, expf, HUGE_VALF, HUGE_VAL, HUGE_VALL
+cdef extern from "<math.h>":
+    double log(double x) nogil
+    float logf(float) nogil
+    double exp(double x) nogil
+    float expf(float) nogil
+    const float HUGE_VALF
+    const double HUGE_VAL
+    const long double HUGE_VALL
 
 c_real_t = ctypes.c_float
 ctypedef float real_t

pyproject.toml

@@ -1,2 +1,2 @@
 [build-system]
-requires = ["cython>=3.0.0", "setuptools", "wheel", "numpy>=1.25", "scipy>=1.11.1"]
+requires = ["cython==0.29.36", "setuptools", "wheel", "numpy>=1.25", "scipy>=1.11.1"]

requirements.txt

@@ -1,5 +1,5 @@
 pandas
 numpy>=1.25
 scipy>=1.11.1
-cython>=3.0.0
-hpfrec>=0.2.3
+cython
+hpfrec>=0.2.10

setup.py

@@ -208,7 +208,7 @@ def test_supports_compile_arg(self, comm, with_omp=False):
 setup(
     name = 'ctpfrec',
     packages = ['ctpfrec'],
-    version = '0.1.17',
+    version = '0.1.18',
     description = 'Collaborative topic Poisson factorization for recommender systems',
     author = 'David Cortes',
     url = 'https://github.com/david-cortes/ctpfrec',