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When Modf is inlined, a fused multiply-subtract can retain extra precision from pow * val and move a half-way fractional part below 0.5. On arm64 and riscv64, round(123.5555, 3) then returns 123.555 instead of 123.556. An explicit float64 conversion rounds the product before Modf examines it. The existing TestRound case covers the regression. Signed-off-by: cl2t <yihong.or@isrc.iscas.ac.cn>
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With Go 1.26.3 on arm64 and Go 1.27.1 on riscv64,
round(123.5555, 3)can return123.555instead of123.556. Aftermath.Modfis inlined, a fused multiply-subtract retains extra precision and moves the fractional part below the rounding threshold.Explicitly convert the product to
float64so it is rounded beforeModfsubtracts its integer part, as required by the Go floating-point rules.Validation:
989da45), the existingTestRoundfails before this change and passes afterward with Go 1.26.3 on darwin/arm64.TZ=UTC(the existingTestHtmlDateexpects that date). Dependencies were tested offline using a temporary modfile pointing to the official cast v1.9.2 archive; repository module files are unchanged.Assisted-by: Codex:GPT-6