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gcvctor: add PGNumericValueExact for the PG-dialect numeric value space - #257
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PGNumericValue formats via spanner.NumericString, silently rounding to the GoogleSQL 9-fractional-digit scale even though PostgreSQL-dialect numeric accepts far more. PGNumericValueExact renders the exact decimal (smallest sufficient scale) and refuses to lose precision: rationals without a finite decimal expansion return the new ErrInexactNumeric and nil returns ErrNilNumeric. MustPGNumericValueExact joins must.go per the fixture convention. Closes #249. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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This pull request introduces PGNumericValueExact and MustPGNumericValueExact to support exact decimal rendering of PostgreSQL-dialect NUMERIC values without losing precision, alongside a helper finiteDecimalScale and corresponding tests. The review feedback suggests a performance optimization in finiteDecimalScale to pre-allocate big.Int variables outside the loop to avoid repeated allocations.
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Closes #249 (filed from the spanpg phase-3 work, where the 9-digit rounding of
PGNumericValuehad to be documented as a hazard on spanpg'sEncodeOptions).Implements option 1 from the issue:
PGNumericValueExact(*big.Rat)renders the exact decimal at the smallest sufficient scale (reduced denominator must factor into 2^a·5^b; otherwise the newErrInexactNumeric), so values the PG-dialectnumerictype can represent exactly are never silently rounded.MustPGNumericValueExactjoins the fixture family. A contrast test pins the rounding behavior this constructor exists to avoid (1e-17→0.000000000underPGNumericValue).Follow-up after release: spanpg updates its
EncodeOptionshazard doc to point here.🤖 Generated with Claude Code