fix: Fix incorrect result from casting double to decimal #12600
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…ubator#12600) Summary: When converting 0.03456789 to DECIMAL(38, 33), the result generated by Velox is inconsistent with Spark and Presto. This discrepancy is caused by precision errors due to long double multiplication. I propose fixing this issue by first converting the result to the target type(int64_t / int128_t) and then applying rescaling. Velox ``` spark.sql("select cast(0.03456789d as decimal(38, 33))").collect res18: Array[org.apache.spark.sql.Row] = Array([0.034567889999999999999845079187456]) ``` Spark ``` spark.sql("select cast(0.03456789d as decimal(38, 33))").collect res16: Array[org.apache.spark.sql.Row] = Array([0.034567890000000000000000000000000]) ``` Presto ``` presto> select cast(0.03456789 as decimal(38, 33)); _col0 ------------------------------------- 0.034567890000000000000000000000000 (1 row) ``` Pull Request resolved: facebookincubator#12600 Reviewed By: kgpai Differential Revision: D71907659 Pulled By: bikramSingh91 fbshipit-source-id: ffaee88c3f1f67a8d0f2e2008550d591ce8b66ca
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When converting 0.03456789 to DECIMAL(38, 33), the result generated by Velox is
inconsistent with Spark and Presto. This discrepancy is caused by precision
errors due to long double multiplication. I propose fixing this issue by first
converting the result to the target type(int64_t / int128_t) and then applying rescaling.
Velox
Spark
Presto