Merge branch 'RoundOffError' into 'master'

Fix RoundOff problems

See merge request pycodegen/pystencils!282

pystencils/backends/cbackend.py

@@ -441,7 +441,7 @@ class CustomSympyPrinter(CCodePrinter):
     def _print_Pow(self, expr):
         """Don't use std::pow function, for small integer exponents, write as multiplication"""
         if not expr.free_symbols:
-            return self._typed_number(expr.evalf(), get_type_of_expression(expr.base))
+            return self._typed_number(expr.evalf(17), get_type_of_expression(expr.base))
 
         if expr.exp.is_integer and expr.exp.is_number and 0 < expr.exp < 8:
             return f"({self._print(sp.Mul(*[expr.base] * expr.exp, evaluate=False))})"
@@ -452,7 +452,7 @@ class CustomSympyPrinter(CCodePrinter):
 
     def _print_Rational(self, expr):
         """Evaluate all rationals i.e. print 0.25 instead of 1.0/4.0"""
-        res = str(expr.evalf().num)
+        res = str(expr.evalf(17))
         return res
 
     def _print_Equality(self, expr):

pystencils/simp/simplifications.py

@@ -234,7 +234,7 @@ def apply_sympy_optimisations(assignments):
 
     # Evaluates all constant terms
     evaluate_constant_terms = ReplaceOptim(lambda e: hasattr(e, 'is_constant') and e.is_constant and not e.is_integer,
-                                           lambda p: p.evalf())
+                                           lambda p: p.evalf(17))
 
     sympy_optimisations = [evaluate_constant_terms] + list(optims_c99)
 

pystencils_tests/test_types.py

@@ -101,8 +101,9 @@ def test_sqrt_of_integer():
     kernel(f=arr_single)
 
     code = ps.get_code_str(kernel.ast)
-
-    assert "1.7320508075688772f" in code
+    # ps.show_code(kernel.ast)
+    # 1.7320508075688772935  --> it is actually correct to round to ...773. This was wrong before !282
+    assert "1.7320508075688773f" in code
     assert 1.7 < arr_single[0] < 1.8