Replace float_endf with a fast C/Cython version

openmc/data/_endf.pyx

@@ -0,0 +1,8 @@
+# cython: c_string_type=str, c_string_encoding=ascii
+
+cdef extern from "endf.c":
+    double cfloat_endf(const char* buffer, int n)
+
+def float_endf(s):
+    cdef const char* c_string = s
+    return cfloat_endf(c_string, len(s))

openmc/data/endf.c

@@ -0,0 +1,37 @@
+#include <stdlib.h>
+
+double cfloat_endf(const char* buffer, int n)
+{
+  char arr[12]; // 11 characters plus a null terminator
+  int j = 0; // current position in arr
+  int found_decimal = 0;
+  int found_exponent = 0;
+  for (int i = 0; i < n; ++i) {
+    // Skip whitespace characters
+    char c = buffer[i];
+    if (c == ' ') continue;
+
+    if (found_decimal) {
+      if (!found_exponent) {
+        if (c == '+' || c == '-') {
+          // In the case that we encounter +/- and we haven't yet encountered
+          // e/E, we manually add it
+          arr[j++] = 'e';
+          found_exponent = 1;
+
+        } else if (c == 'e' || c == 'E') {
+          found_exponent = 1;
+        }
+      }
+    } else if (c == '.') {
+      found_decimal = 1;
+    }
+
+    // Copy character
+    arr[j++] = c;
+  }
+
+  // Done copying. Add null terminator and convert to double
+  arr[j] = '\0';
+  return atof(arr);
+}

openmc/data/endf.py

@@ -20,6 +20,11 @@ from numpy.polynomial.polynomial import Polynomial
 from .data import ATOMIC_SYMBOL, gnd_name
 from .function import Tabulated1D, INTERPOLATION_SCHEME
 from openmc.stats.univariate import Uniform, Tabular, Legendre
+try:
+    from ._endf import float_endf
+    _CYTHON = True
+except ImportError:
+    _CYTHON = False
 
 
 _LIBRARY = {0: 'ENDF/B', 1: 'ENDF/A', 2: 'JEFF', 3: 'EFF',
@@ -69,7 +74,7 @@ SUM_RULES = {1: [2, 3],
 ENDF_FLOAT_RE = re.compile(r'([\s\-\+]?\d*\.\d+)([\+\-]) ?(\d+)')
 
 
-def float_endf(s):
+def py_float_endf(s):
     """Convert string of floating point number in ENDF to float.
 
     The ENDF-6 format uses an 'e-less' floating point number format,
@@ -92,6 +97,10 @@ def float_endf(s):
     return float(ENDF_FLOAT_RE.sub(r'\1e\2\3', s))
 
 
+if not _CYTHON:
+    float_endf = py_float_endf
+
+
 def int_endf(s):
     """Convert string of integer number in ENDF to int.
 

setup.py

@@ -68,10 +68,10 @@ kwargs = {
     },
 }
 
-# If Cython is present, add resonance reconstruction capability
+# If Cython is present, add resonance reconstruction and fast float_endf
 if have_cython:
     kwargs.update({
-        'ext_modules': cythonize('openmc/data/reconstruct.pyx'),
+        'ext_modules': cythonize('openmc/data/*.pyx'),
         'include_dirs': [np.get_include()]
     })
 

tests/unit_tests/test_endf.py

@@ -9,6 +9,8 @@ def test_float_endf():
     assert endf.float_endf('6.022-23') == approx(6.022e-23)
     assert endf.float_endf(' +1.01+ 2') == approx(101.0)
     assert endf.float_endf(' -1.01- 2') == approx(-0.0101)
+    assert endf.float_endf('+ 2 . 3+ 1') == approx(23.0)
+    assert endf.float_endf('-7 .8 -1') == approx(-0.78)
 
 
 def test_int_endf():