Clarify semantics of fancy integer division functions.

Closes #88 (closed).

The goal of these functions is to provide fast, fp-free functions for semi-complicated semantics on positive integers (The old implementation did not behave sensibly for negative input). This MR clarifies the names and docstrings of the fancy integer divisions to make it clear that negative input is not always expected. Furthermore, the implementation is changed such that no remainders or conditionals must be evaluated.

The old names are still available but issue deprecation warnings.

src/pystencils/backend/kernelcreation/freeze.py

@@ -272,7 +272,7 @@ class FreezeExpressions:
 
     def map_TypedSymbol(self, expr: TypedSymbol):
         dtype = expr.dtype
-        
+
         match dtype:
             case DynamicType.NUMERIC_TYPE:
                 dtype = self._ctx.default_dtype
@@ -422,12 +422,19 @@ class FreezeExpressions:
                 return PsBitwiseOr(*args)
             case integer_functions.int_power_of_2():
                 return PsLeftShift(PsExpression.make(PsConstant(1)), args[0])
-            # TODO: what exactly are the semantics?
-            # case integer_functions.modulo_floor():
-            # case integer_functions.div_floor()
-            # TODO: requires if *expression*
-            # case integer_functions.modulo_ceil():
-            # case integer_functions.div_ceil():
+            case integer_functions.round_to_multiple_towards_zero():
+                return PsIntDiv(args[0], args[1]) * args[1]
+            case integer_functions.ceil_to_multiple():
+                return (
+                    PsIntDiv(
+                        args[0] + args[1] - PsExpression.make(PsConstant(1)), args[1]
+                    )
+                    * args[1]
+                )
+            case integer_functions.div_ceil():
+                return PsIntDiv(
+                    args[0] + args[1] - PsExpression.make(PsConstant(1)), args[1]
+                )
             case AddressOf():
                 return PsAddressOf(*args)
             case _: