Remove the Number static constructor

[tannergooding]

Moves Number's primitive Decimal32/64/128 coefficient data to RVA-backed spans and computes the remaining small structured constants on demand. Managed caches that still require initialization are isolated in nested holder types, so Number no longer has a static constructor and unused data can be trimmed.

Formatting patterns now use switch-selected RVA byte spans rather than managed string arrays. Direct byte handling was within benchmark noise versus the prior implementation: currency -1.9%, number -1.2%, and percent +0.2%, with unchanged allocations.

Validated CoreCLR, NativeAOT, and Mono builds and all 77,366 System.Runtime.Tests.

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[tannergooding]

This was raised by @MichalStrehovsky in MichalStrehovsky/rt-sz#247 as caused by #131019

Basically the issue was some new static readonly field introduced. So this PR fully removes all the static fields, ensuring we either use RVA statics or a helper lookup so that it can be fully avoided and there is now no ..ctor for Number.

[Copilot]

Pull request overview

Refactors System.Number implementation details to eliminate the type’s static constructor by moving previously eagerly-initialized caches/tables into RVA-backed spans and nested holder types, computing the remaining small constants on demand. This primarily targets improved trimming (unused data not rooted by .cctor) while preserving existing formatting/math behavior.

Changes:

• Replaces managed string-array formatting patterns with switch-selected ReadOnlySpan<byte> format templates in the shared formatting helper.
• Moves small number and Mono “TwoDigits” caches behind nested holder types to avoid Number-level eager initialization.
• Converts multiple Decimal IEEE754 coefficient/constant tables (trig/log/pow/exp/hyper) from static readonly arrays to span-backed representations plus small on-demand constant getters.

Show a summary per file

File	Description
src/libraries/System.Private.CoreLib/src/System/Number.Formatting.cs	Moves small-number and Mono TwoDigits caches into nested holders to avoid Number static initialization.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.Transcendental.cs	Updates call sites to use on-demand pi / inverse-trig constants instead of static arrays.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Trig.cs	Switches trig coefficient tables to span-backed coefficient data.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Sqrt.cs	Replaces the sqrt coefficient struct table with split span-backed AB/C coefficient data.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Pow.cs	Converts pow coefficient tables to span-backed coefficients.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128PiTrig.cs	Replaces static pi-fraction constants with an on-demand getter and makes small constants computed properties.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Log.cs	Converts log coefficient table to span-backed coefficients.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128InvTrig.cs	Replaces inverse-trig constants array with an on-demand getter; converts coefficient tables to span-backed coefficients.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Hyper.cs	Converts sinh/cosh coefficient tables to span-backed coefficients.
src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Exp.cs	Adds a shared span-casting helper for fixed coefficients and converts exp/exp10 tables to span-backed coefficients.
src/libraries/Common/src/System/Number.Formatting.Common.cs	Replaces currency/number/percent format string arrays with switch-selected ReadOnlySpan<byte> templates.

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 0
• Review effort level: Lite

[Copilot]

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

src/libraries/System.Private.CoreLib/src/System/Number.DecimalIeee754.DiyFp128Exp.cs:39

• DiyFp128FixedCoefficients relies on MemoryMarshal.Cast<ulong, DiyFp128FixedCoefficient> which assumes DiyFp128FixedCoefficient stays exactly 2 ulongs (16 bytes). Adding an explicit size assertion makes this helper robust against future edits to the struct that would otherwise silently reinterpret data incorrectly.

    private static ReadOnlySpan<DiyFp128FixedCoefficient> DiyFp128FixedCoefficients(ReadOnlySpan<ulong> coefficients)
    {
        Debug.Assert((coefficients.Length & 1) == 0);

        return MemoryMarshal.Cast<ulong, DiyFp128FixedCoefficient>(coefficients);
    }

• Files reviewed: 11/11 changed files
• Comments generated: 1
• Review effort level: Lite

[EgorBo]

@MihuBot

[EgorBo]

not sure if perf matters for this, but I am sure this is unlikely to inline for NAOT without PGO (and others).

[tannergooding]

It should be fine if it doesn't inline, the index is never constant and so its a "bounds check" either way.

[MichalStrehovsky]

This was raised by @MichalStrehovsky in MichalStrehovsky/rt-sz#247 as caused by #131019

Looks like this fully fixes the regression: MichalStrehovsky/rt-sz#249