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Write went through decimal.StringFixed, which rounds via big.Int and builds intermediate strings: 11 allocs/op for a typical price. Format directly from the int64 coefficient when it fits, rounding half away from zero as StringFixed does, and fall back otherwise (large coefficients, negative or >19 scale). BenchmarkFIXDecimalWrite: 203ns, 208B, 11 allocs -> 21ns, 24B, 2 allocs. A differential test checks the result against StringFixed over edge coefficients, exponents and scales.
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Closes #786.
FIXDecimal.Writeformats viadecimal.StringFixed, which rounds throughbig.Intand builds intermediate strings. This adds a fast path that formats directly from the int64 coefficient, rounding half away from zero asStringFixeddoes. It falls back to the existing path for coefficients beyond int64, negative scale, and scale >= 20, so output is unchanged.Benchmark (
BenchmarkFIXDecimalWrite,benchstat, 10 runs):Tests:
TestFIXDecimalWriteMatchesStringFixedcompares againstStringFixedover edge coefficients (includingMinInt64), exponents -25..25 and several scales, including rounding ties and negative values that round to zero.go test -raceandgo vetpass.log/mongofails onmaintoo, since it needs a MongoDB instance.