Ben Becker created DRILL-261:
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Summary: Implement support for DECIMAL type
Key: DRILL-261
URL: https://issues.apache.org/jira/browse/DRILL-261
Project: Apache Drill
Issue Type: Task
Reporter: Ben Becker
Many functions and operators in Drill need to handle decimal types. This may
mean two formats; an expanded format for use during processing, and a compact
format for efficient representation on disk.
Postgres' compact (on-disk) format for the decimal types NumericShort and
NumericLong generally fit into a 64 bits:
{noformat}
1 bit for sign
6 bits for scale in NumericShort; 16 bits in NumericLong
7 bits for weight in NumericShort; 16 bits in NumericLong
16 bits for the digits
{noformat}
The expanded (in-memory) format in Postgres is defined in {{numeric.c}} as
follows:
{noformat}
typedef struct NumericVar
{
int ndigits; /* # of digits in digits[] - can be 0! */
int weight; /* weight of first digit */
int sign; /* NUMERIC_POS, NUMERIC_NEG, or NUMERIC_NAN */
int dscale; /* display scale */
NumericDigit *buf; /* start of palloc'd space for digits[] */
NumericDigit *digits; /* base-NBASE digits */
} NumericVar;
{noformat}
Additional notes and links to related published papers are in the
aforementioned source file.
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