[arrow] branch master updated: ARROW-2387: [Python] Flip test for rescale loss if value < 0

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The following commit(s) were added to refs/heads/master by this push:
     new 7de1264  ARROW-2387: [Python] Flip test for rescale loss if value < 0
7de1264 is described below

commit 7de1264c7230f0a9ae8261bb08ea6b57d2b51e7c
Author: Ben Wolfson <be...@affirm.com>
AuthorDate: Fri Apr 13 16:02:28 2018 -0400

    ARROW-2387: [Python] Flip test for rescale loss if value < 0
    
    Author: Ben Wolfson <be...@affirm.com>
    
    Closes #1832 from bwo/ARROW-2387 and squashes the following commits:
    
    6b69be34 <Ben Wolfson> address comments
    30a02fb7 <Ben Wolfson> formatting of python-test.cc
    793b416d <Ben Wolfson> flip test for rescale loss if value < 0
---
 cpp/src/arrow/python/python-test.cc | 10 ++++++++++
 cpp/src/arrow/util/decimal.cc       |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/cpp/src/arrow/python/python-test.cc b/cpp/src/arrow/python/python-test.cc
index 293255b..3ea814f 100644
--- a/cpp/src/arrow/python/python-test.cc
+++ b/cpp/src/arrow/python/python-test.cc
@@ -247,6 +247,16 @@ TEST_F(DecimalTest, FromPythonDecimalRescaleTruncateable) {
   ASSERT_EQ(100, value.low_bits());
 }
 
+TEST_F(DecimalTest, FromPythonNegativeDecimalRescale) {
+  Decimal128 value;
+  OwnedRef python_decimal(this->CreatePythonDecimal("-1.000"));
+  auto type = ::arrow::decimal(10, 9);
+  const auto& decimal_type = static_cast<const DecimalType&>(*type);
+  ASSERT_OK(
+      internal::DecimalFromPythonDecimal(python_decimal.obj(), decimal_type, &value));
+  ASSERT_EQ(-1000000000, value);
+}
+
 TEST_F(DecimalTest, TestOverflowFails) {
   Decimal128 value;
   OwnedRef python_decimal(
diff --git a/cpp/src/arrow/util/decimal.cc b/cpp/src/arrow/util/decimal.cc
index 9e5e3dd..668da6f 100644
--- a/cpp/src/arrow/util/decimal.cc
+++ b/cpp/src/arrow/util/decimal.cc
@@ -843,7 +843,7 @@ static bool RescaleWouldCauseDataLoss(const Decimal128& value, int32_t delta_sca
   }
 
   *result = value * multiplier;
-  return *result < value;
+  return (value < 0) ? *result > value : *result < value;
 }
 
 Status Decimal128::Rescale(int32_t original_scale, int32_t new_scale,

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