Add ceil and floor as uom rounding methods

issue6222
review27041002

CHANGELOG

@@ -1,3 +1,5 @@
+* Add ceil and floor as uom rounding
+
 Version 4.2.0 - 2016-11-28
 * Bug fixes (see mercurial logs for details)
 * Add relate from Template to Products

tests/test_product.py

@@ -313,24 +313,27 @@ class ProductTestCase(ModuleTestCase):
                     ], count=True), 2)
 
     @with_transaction()
-    def test_uom_round(self):
-        'Test uom round function'
+    def test_uom_rounding(self):
+        'Test uom rounding functions'
         pool = Pool()
         Uom = pool.get('product.uom')
         tests = [
-            (2.53, .1, 2.5),
-            (3.8, .1, 3.8),
-            (3.7, .1, 3.7),
-            (1.3, .5, 1.5),
-            (1.1, .3, 1.2),
-            (17, 10, 20),
-            (7, 10, 10),
-            (4, 10, 0),
-            (17, 15, 15),
-            (2.5, 1.4, 2.8),
+            (2.53, .1, 2.5, 2.6, 2.5),
+            (3.8, .1, 3.8, 3.8, 3.8),
+            (3.7, .1, 3.7, 3.7, 3.7),
+            (1.3, .5, 1.5, 1.5, 1.0),
+            (1.1, .3, 1.2, 1.2, 0.9),
+            (17, 10, 20, 20, 10),
+            (7, 10, 10, 10, 0),
+            (4, 10, 0, 10, 0),
+            (17, 15, 15, 30, 15),
+            (2.5, 1.4, 2.8, 2.8, 1.4),
             ]
-        for number, precision, result in tests:
-            self.assertEqual(Uom(rounding=precision).round(number), result)
+        for number, precision, round, ceil, floor in tests:
+            uom = Uom(rounding=precision)
+            self.assertEqual(uom.round(number), round)
+            self.assertEqual(uom.ceil(number), ceil)
+            self.assertEqual(uom.floor(number), floor)
 
     @with_transaction()
     def test_product_order(self):

uom.py

@@ -3,6 +3,7 @@
 from __future__ import division
 from decimal import Decimal
 from sql import Table
+from math import ceil, floor, log10
 
 from trytond.model import ModelView, ModelSQL, fields, Check
 from trytond.pyson import Eval
@@ -135,12 +136,13 @@ class Uom(ModelSQL, ModelView):
             ]
 
     def round(self, number):
-        precision = self.rounding
-        i, d = divmod(precision, 1)
-        base = round(number / precision)
-        # Instead of multiply by the decimal part, we must divide by the
-        # integer to avoid precision lost due to float
-        return (base * i) + ((base / (1 / d)) if d != 0 else 0)
+        return _round(self, number, func=round)
+
+    def ceil(self, number):
+        return _round(self, number, func=ceil)
+
+    def floor(self, number):
+        return _round(self, number, func=floor)
 
     @classmethod
     def validate(cls, uoms):
@@ -265,3 +267,24 @@ class Uom(ModelSQL, ModelView):
             new_price = new_price / Decimal(rate_format % to_uom.rate)
 
         return new_price
+
+
+def _round(uom, number, func=round):
+    precision = uom.rounding
+    # Convert precision into an integer greater than 1 to avoid precision lost.
+    # This works for most cases because rounding is often: n * 10**i
+    if precision < 1:
+        exp = -floor(log10(precision))
+        factor = 10 ** exp
+        number *= factor
+        precision *= factor
+    else:
+        factor = 1
+    # Divide by factor which is an integer to avoid precision lost due to
+    # multiplication by float < 1.
+    # example:
+    # >>> 3 * 0.1
+    # 0.30000000000000004
+    # >>> 3 / 10.
+    # 0.3
+    return func(number / precision) * precision / factor