[go] strconv: clean up powers-of-10 table, tests

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Russ Cox (Gerrit)

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Oct 22, 2025, 4:50:48 PM (17 hours ago) Oct 22

to Russ Cox, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, Go LUCI, Alan Donovan, David Chase, golang-co...@googlegroups.com

Russ Cox submitted the change

Change information

Commit message:

strconv: clean up powers-of-10 table, tests

Both Eisel-Lemire and Ryu depend on a table of
truncated 128-bit mantissas of powers of 10,
and so will Dragonbox.

This CL:
 - Moves the table to a separate file, so it doesn't look tied to Eisel-Lemire.
 - Introduces a uint128 type in math.go for the table values,
   since .Hi and .Lo are clearer than [1] and [0].
 - Generates the table from a standalone generator pow10gen.go.
 - Adds a new pow10 function in math.go to handle table access details.
 - Factors a 64x128->192-bit multiply into umul192 in math.go.
 - Moves multiplication by log₁₀ 2 and log₂ 10 into math.go.
 - Introduces an import_test.go to avoid having to type differently
   cased names in test code versus regular code.
 - Introduces named constants for the floating-point size parameters.
   Previously these were only in the floatInfo global variables.
 - Changes the BenchmarkAppendUintVarlen subtest names
   to be more useful.