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Posted to github@arrow.apache.org by "huberylee (via GitHub)" <gi...@apache.org> on 2023/10/31 08:39:54 UTC
Re: [PR] GH-35576: [C++] Make Decimal{128,256}::FromReal more accurate [arrow]
huberylee commented on code in PR #35997:
URL: https://github.com/apache/arrow/pull/35997#discussion_r1377227122
##########
cpp/src/arrow/util/decimal_test.cc:
##########
@@ -868,24 +867,29 @@ template <typename T>
class TestDecimalFromRealFloat : public ::testing::Test {
protected:
std::vector<FromFloatTestParam> GetValues() {
- return {// 2**63 + 2**40 (exactly representable in a float's 24 bits of precision)
- FromFloatTestParam{9.223373e+18f, 19, 0, "9223373136366403584"},
- FromFloatTestParam{-9.223373e+18f, 19, 0, "-9223373136366403584"},
- FromFloatTestParam{9.223373e+14f, 19, 4, "922337313636640.3584"},
- FromFloatTestParam{-9.223373e+14f, 19, 4, "-922337313636640.3584"},
- // 2**64 - 2**40 (exactly representable in a float)
- FromFloatTestParam{1.8446743e+19f, 20, 0, "18446742974197923840"},
- FromFloatTestParam{-1.8446743e+19f, 20, 0, "-18446742974197923840"},
- // 2**64 + 2**41 (exactly representable in a float)
- FromFloatTestParam{1.8446746e+19f, 20, 0, "18446746272732807168"},
- FromFloatTestParam{-1.8446746e+19f, 20, 0, "-18446746272732807168"},
- FromFloatTestParam{1.8446746e+15f, 20, 4, "1844674627273280.7168"},
- FromFloatTestParam{-1.8446746e+15f, 20, 4, "-1844674627273280.7168"},
- // Almost 10**38 (minus 2**103)
- FromFloatTestParam{9.999999e+37f, 38, 0,
- "99999986661652122824821048795547566080"},
- FromFloatTestParam{-9.999999e+37f, 38, 0,
- "-99999986661652122824821048795547566080"}};
+ return {
+ // -- Stress the 24 bits of precision of a float
+ // 2**63 + 2**40
+ FromFloatTestParam{9.223373e+18f, 19, 0, "9223373136366403584"},
Review Comment:
Hi, the expected return value of ``FromFloatTestParam{5.76460752e13f, 18, 4, "57646075230342.3488"}`` is ``57646073774080.0000``, which seems different from the original value, does that meet expectations？
##########
cpp/src/arrow/util/decimal_test.cc:
##########
@@ -868,24 +867,29 @@ template <typename T>
class TestDecimalFromRealFloat : public ::testing::Test {
protected:
std::vector<FromFloatTestParam> GetValues() {
- return {// 2**63 + 2**40 (exactly representable in a float's 24 bits of precision)
- FromFloatTestParam{9.223373e+18f, 19, 0, "9223373136366403584"},
- FromFloatTestParam{-9.223373e+18f, 19, 0, "-9223373136366403584"},
- FromFloatTestParam{9.223373e+14f, 19, 4, "922337313636640.3584"},
- FromFloatTestParam{-9.223373e+14f, 19, 4, "-922337313636640.3584"},
- // 2**64 - 2**40 (exactly representable in a float)
- FromFloatTestParam{1.8446743e+19f, 20, 0, "18446742974197923840"},
- FromFloatTestParam{-1.8446743e+19f, 20, 0, "-18446742974197923840"},
- // 2**64 + 2**41 (exactly representable in a float)
- FromFloatTestParam{1.8446746e+19f, 20, 0, "18446746272732807168"},
- FromFloatTestParam{-1.8446746e+19f, 20, 0, "-18446746272732807168"},
- FromFloatTestParam{1.8446746e+15f, 20, 4, "1844674627273280.7168"},
- FromFloatTestParam{-1.8446746e+15f, 20, 4, "-1844674627273280.7168"},
- // Almost 10**38 (minus 2**103)
- FromFloatTestParam{9.999999e+37f, 38, 0,
- "99999986661652122824821048795547566080"},
- FromFloatTestParam{-9.999999e+37f, 38, 0,
- "-99999986661652122824821048795547566080"}};
+ return {
+ // -- Stress the 24 bits of precision of a float
+ // 2**63 + 2**40
+ FromFloatTestParam{9.223373e+18f, 19, 0, "9223373136366403584"},
Review Comment:
Hi, the expected return value of ``FromFloatTestParam{5.76460752e13f, 18, 4, "57646075230342.3488"}`` is ``57646073774080.0000``, which seems different from the original value, does that meet expectations？
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