From dcb5ff6eacc63cebdc03f8615b18a002cb6ad23d Mon Sep 17 00:00:00 2001
From: Olivier Dony <odo@openerp.com>
Date: Mon, 14 Nov 2011 17:36:17 +0100
Subject: [PATCH] [IMP] res.currency,base: factor out float rounding methods in
 tools to allow use without currency

Pending: addition of tests

bzr revid: odo@openerp.com-20111114163617-kw7u8rxcie7m2hj5
---
 openerp/addons/base/res/res_currency.py | 41 ++++++++++---
 openerp/tools/misc.py                   | 79 ++++++++++++++++++++++++-
 2 files changed, 111 insertions(+), 9 deletions(-)

diff --git a/openerp/addons/base/res/res_currency.py b/openerp/addons/base/res/res_currency.py
index 32aa387e828..c0a2bebc104 100644
--- a/openerp/addons/base/res/res_currency.py
+++ b/openerp/addons/base/res/res_currency.py
@@ -24,7 +24,7 @@ import netsvc
 from osv import fields, osv
 import tools
 
-from tools.misc import currency
+from tools.misc import currency, float_round, float_is_zero, float_compare
 from tools.translate import _
 
 CURRENCY_DISPLAY_PATTERN = re.compile(r'(\w+)\s*(?:\((.*)\))?')
@@ -127,15 +127,40 @@ class res_currency(osv.osv):
         return [(x['id'], tools.ustr(x['name']) + (x['symbol'] and (' (' + tools.ustr(x['symbol']) + ')') or '')) for x in reads]
 
     def round(self, cr, uid, currency, amount):
-        if currency.rounding == 0:
-            return 0.0
-        else:
-            # /!\ First member below must be rounded to full unit!
-            # Do not pass a rounding digits value to round()
-            return round(amount / currency.rounding) * currency.rounding
+        """Return ``amount`` rounded  according to ``currency``'s
+           rounding rules, also minimizing IEEE-754 floating point
+           representation errors.
+
+           :param browse_record currency: currency for which we are rounding
+           :param float amount: the amount to round
+           :return: rounded float
+        """
+        return float_round(amount, precision_rounding=currency.rounding)
+
+    def compare_amounts(self, cr, uid, currency, amount1, amount2):
+        """Compare ``amount1`` and ``amount2`` according to ``currency``'s
+           rounding rules, and return (resp.) -1, 0 or 1, if ``amount1``
+           is (resp.) lower than, equal to, or greater than ``amount2``.
+
+           For example 1.432 and 1.431 are equal if currency is rounded to
+           2 digits, so this method would return 0
+
+           :param browse_record currency: currency for which we are rounding
+           :param float amount1: first amount to compare
+           :param float amount2: second amount to compare
+           :return: (resp.) -1, 0 or 1, if ``amount1`` is (resp.) lower than,
+                    equal to, or greater than ``amount2``, according to
+                    ``currency``'s rounding.
+        """
+        return float_compare(amount1, amount2, precision_rounding=currency.rounding)
 
     def is_zero(self, cr, uid, currency, amount):
-        return abs(self.round(cr, uid, currency, amount)) < currency.rounding
+        """Returns true if ``amount`` is small enough to be treated as
+           zero according to ``currency``'s rounding rules.
+           :param browse_record currency: currency for which we are rounding
+           :param float amount: amount to compare with currency's zero
+        """
+        return float_is_zero(amount, precision_rounding=currency.rounding)
 
     def _get_conversion_rate(self, cr, uid, from_currency, to_currency, context=None):
         if context is None:
diff --git a/openerp/tools/misc.py b/openerp/tools/misc.py
index dbccbe5b217..ae28567e19b 100644
--- a/openerp/tools/misc.py
+++ b/openerp/tools/misc.py
@@ -1200,4 +1200,81 @@ class UnquoteEvalContext(defaultdict):
     def __missing__(self, key):
         return unquote(key)
 
-# vim:expandtab:smartindent:tabstop=4:softtabstop=4:shiftwidth=4:
+def _float_check_precision(precision_digits=None, precision_rounding=None):
+    assert (precision_digits is not None or precision_rounding is not None) and \
+        not (precision_digits and precision_rounding),\
+         "exactly one of precision_digits and precision_rounding must be specified"
+    if precision_digits is not None:
+        return 10 ** -precision_digits
+    return precision_rounding
+
+def float_round(amount, precision_digits=None, precision_rounding=None):
+    """Return ``amount`` rounded to ``precision_digits``
+       decimal digits, minimizing IEEE-754 floating point representation
+       errors.
+       Precision must be given by ``precision_digits`` or ``precision_rounding``,
+       not both!
+       Example on Python 2.7.2::
+
+          >>> round_float(2.675)
+          2.68
+          >>> round(2.675,2)
+          2.67
+
+       :param float amount: the amount to round
+       :param int precision_digits: number of decimal digits to round to.
+       :param float precision_rounding: decimal number representing the minimum
+           non-zero value at the desired precision (for example, 0.01 for a 
+           2-digit precision).
+       :return: rounded float
+    """
+    rounding_factor = _float_check_precision(precision_digits=precision_digits,
+                                             precision_rounding=precision_rounding)
+    if rounding_factor == 0: return 0.0
+    # /!\ First member below must be rounded to full unit!
+    # Do not pass rounding digits to round()!
+    return round(amount / rounding_factor) * rounding_factor
+
+def float_is_zero(amount, precision_digits=None, precision_rounding=None):
+    """Returns true if ``amount`` is small enough to be treated as
+       zero at the given precision.
+       Precision must be given by ``precision_digits`` or ``precision_rounding``,
+       not both!
+
+       :param int precision_digits: number of decimal digits to round to.
+       :param float precision_rounding: decimal number representing the minimum
+           non-zero value at the desired precision (for example, 0.01 for a 
+           2-digit precision).
+       :param float amount: amount to compare with currency's zero
+       :return: True if ``amount`` is considered 0
+    """
+    rounding_factor = _float_check_precision(precision_digits=precision_digits,
+                                             precision_rounding=precision_rounding)
+    return abs(float_round(amount, precision_rounding=rounding_factor)) < rounding_factor
+
+def float_compare(amount1, amount2, precision_digits=None, precision_rounding=None):
+    """Compare ``amount1`` and ``amount2`` according
+       to the given precision.
+       Precision must be given by ``precision_digits`` or ``precision_rounding``,
+       not both!
+
+       For example 1.432 and 1.431 are equal at 2 digits precision,
+       so this method would return 0
+
+       :param int precision_digits: number of decimal digits to round to.
+       :param float precision_rounding: decimal number representing the minimum
+           non-zero value at the desired precision (for example, 0.01 for a 
+           2-digit precision).
+       :param float amount1: first amount to compare
+       :param float amount2: second amount to compare
+       :return: (resp.) -1, 0 or 1, if ``amount1`` is (resp.) lower than,
+           equal to, or greater than ``amount2``, at the given precision.
+    """
+    rounding_factor = _float_check_precision(precision_digits=precision_digits,
+                                             precision_rounding=precision_rounding)
+    delta = amount1 - amount2
+    if float_is_zero(delta, precision_rounding=rounding_factor): return 0
+    delta = float_round(delta, precision_rounding=rounding_factor)
+    return -1 if delta < 0 else 1
+
+# vim:expandtab:smartindent:tabstop=4:softtabstop=4:shiftwidth=4:
\ No newline at end of file