cmd/compile,runtime: implement uint64->float32 correctly on 32-bit archs

The old way of implementing it, float32(float64(x)), involves 2 roundings
which can cause accuracy errors in some strange cases. Implement a runtime
version of [u]int64tofloat32 which only does one rounding.

Fixes #48807

Change-Id: Ie580be480bee4f3a479e58ef8dce23032f231704
Reviewed-on: https://go-review.googlesource.com/c/go/+/354429
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
5 files changed
tree: f79c8afe98db2f4ec23f2a332abfdb23b8528b8b
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. AUTHORS
  11. codereview.cfg
  12. CONTRIBUTING.md
  13. CONTRIBUTORS
  14. LICENSE
  15. PATENTS
  16. README.md
  17. SECURITY.md
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