[python-arrayfire] 70/250: Improve handling of negative steps in sequences

[Ghislain Vaillant]

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ghisvail-guest pushed a commit to branch debian/master
in repository python-arrayfire.

commit f0d50c3e52f66ed35329caa81657a03a7a019ba0
Author: Filipe Maia <filipe.c.maia at gmail.com>
Date:   Fri Aug 28 14:42:59 2015 +0200

    Improve handling of negative steps in sequences
---
 arrayfire/index.py | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arrayfire/index.py b/arrayfire/index.py
index 1a17100..1cacc65 100644
--- a/arrayfire/index.py
+++ b/arrayfire/index.py
@@ -10,6 +10,7 @@ from .library import *
 from .util import *
 from .base import *
 from .broadcast import *
+import math
 
 class Seq(ct.Structure):
     _fields_ = [("begin", ct.c_double),
@@ -18,7 +19,6 @@ class Seq(ct.Structure):
 
     def __init__ (self, S):
         num = __import__("numbers")
-
         self.begin = ct.c_double( 0)
         self.end   = ct.c_double(-1)
         self.step  = ct.c_double( 1)
@@ -27,12 +27,14 @@ class Seq(ct.Structure):
             self.begin = ct.c_double(S)
             self.end   = ct.c_double(S)
         elif isinstance(S, slice):
+            if (S.step is not None):
+                self.step  = ct.c_double(S.step)
+                if(S.step < 0):
+                    self.begin, self.end = self.end, self.begin
             if (S.start is not None):
                 self.begin = ct.c_double(S.start)
             if (S.stop is not None):
-                self.end   = ct.c_double(S.stop - 1)
-            if (S.step is not None):
-                self.step  = ct.c_double(S.step)
+                self.end = ct.c_double(S.stop - math.copysign(1, self.step))
         else:
             raise IndexError("Invalid type while indexing arrayfire.array")
 

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