acdream/src/AcDream.Core/Physics/MovementSystem.cs

using System;

namespace AcDream.Core.Physics;

/// <summary>
/// Retail <c>MovementSystem</c> (named-retail decomp pc 695958+): the pure
/// formula layer <c>PlayerWeenie</c> (the CACQualities-shaped composition)
/// calls once burden, skill, and stamina inputs are assembled. See
/// <c>docs/research/2026-07-30-stat-coupled-movement-pseudocode.md</c> §6.
///
/// <para>
/// <b>x87-mush disclosure:</b> <see cref="GetRunRate"/>'s general-case
/// arithmetic and <see cref="JumpStaminaCost"/>'s <c>pk!=0</c> branch are
/// entirely dropped by the BN decompiler (not partially garbled — the
/// operand expressions never survive translation, unlike the polarity-only
/// ambiguities elsewhere in this port). Both are cross-referenced against
/// <c>references/ACE/Source/ACE.Server/Physics/Animation/MovementSystem.cs</c>,
/// which already matched this exact acdream port's PRE-P1 code
/// (<c>PlayerWeenie.GetRunRate</c>/<c>GetJumpHeight</c> already cited "decompiled
/// + ACE MovementSystem" before this slice) — no behavior change for the
/// formulas already live; only the retail-named surface and the 3rd/4th
/// <c>scaling</c> parameters (every known call site passes <c>1f</c>) are new.
/// </para>
/// </summary>
public static class MovementSystem
{
    /// <summary>
    /// <c>MovementSystem::GetRunRate</c> 0x006b0950. The 800 branch is an
    /// EXACT-EQUALITY sentinel, not a cap: raw byte decode of the PDB-paired
    /// binary (#266, 2026-07-30) shows <c>fild skill; fcom [800f]; fnstsw;
    /// test ah, 0x44; jp general</c> — the C2/C3 parity idiom that falls
    /// through to <c>18/4</c> ONLY when skill == 800 (&lt;, &gt;, and
    /// unordered all take the general path). <c>InqMaxRunRate</c> (0x00591b20)
    /// passes skill=9999 and therefore gets the general formula's ~3.6961,
    /// NOT 4.5. The general-path arithmetic is byte-verified
    /// instruction-by-instruction: <c>(loadMod * (skill/(skill+200) * 11) +
    /// 4) / scaling / 4</c>.
    /// </summary>
    /// <remarks>
    /// ACE's <c>MovementSystem.GetRunRate</c> reads this branch as
    /// <c>&gt;= 800</c> ("max run speed?") — that is ACE's misread of the
    /// same x87 mush, NOT a tiebreaker. Porting <c>&gt;=</c> made every
    /// maxed character run a flat 4.5 (vs retail's ~3.70) and erased the
    /// vitae speed differential entirely (#266). Do not "fix" this back
    /// from ACE.
    /// </remarks>
    public static float GetRunRate(float burden, int runSkill, float scaling = 1f)
    {
        if (runSkill == 800)
            return 18f / 4f;

        float loadMod = EncumbranceSystem.LoadMod(burden);
        return ((loadMod * ((float)runSkill / (runSkill + 200) * 11f) + 4f) / scaling) / 4f;
    }

    /// <summary>
    /// <c>MovementSystem::GetJumpHeight</c> 0x006b09b0. Fully readable except
    /// the extent-clamp micro-branch (x87 mush, ACE's <c>Math.Clamp(power,0,1)</c>
    /// is the tiebreaker — matches the pre-P1 acdream port unchanged).
    /// </summary>
    public static float GetJumpHeight(
        float burden,
        int jumpSkill,
        float power,
        float scaling = 1f)
    {
        power = Math.Clamp(power, 0f, 1f);
        float loadMod = EncumbranceSystem.LoadMod(burden);
        float result = loadMod
            * ((float)jumpSkill / (jumpSkill + 1300f) * 22.2f + 0.05f)
            * power
            / scaling;
        return result < 0.35f ? 0.35f : result;
    }

    /// <summary>
    /// <c>MovementSystem::JumpStaminaCost</c> 0x006b0a40. The <c>pk==0</c>
    /// branch is fully readable: <c>ceil((load + 0.5) * power * 8 + 2)</c> —
    /// note <c>load</c> (not <c>power</c>) carries the <c>+0.5</c>; the
    /// campaign plan's shorthand had the operands swapped (see pseudocode
    /// doc §6). The <c>pk!=0</c> branch is entirely dropped by BN; ACE's
    /// <c>(power+1.0)*100.0</c> is the tiebreaker. <paramref name="pk"/> is
    /// the real <c>PlayerKillerStatus</c>/<c>LastPkAttackTimestamp</c>
    /// 20-second-window predicate as of TS-23 (Campaign P Slice P3,
    /// 2026-07-30) — see <see cref="PlayerWeenie.JumpStaminaCost"/>.
    /// </summary>
    public static int JumpStaminaCost(float power, float burden, bool pk)
    {
        if (pk)
            return (int)((power + 1.0f) * 100.0f);

        return (int)Math.Ceiling((burden + 0.5f) * power * 8f + 2f);
    }

    /// <summary>
    /// <c>MovementSystem::GetJumpPower</c> — the algebraic inverse of
    /// <see cref="JumpStaminaCost"/>, solving for the extent affordable at a
    /// given stamina. Present in ACE (uncommented, live utility) but its
    /// retail call site is the charge-power-meter UI outside
    /// <c>CMotionInterp</c> (0x0056afac, out of R3/P1 scope — see
    /// <c>ChargeJump</c>'s doc comment in <c>MotionInterpreter.cs</c>). Not
    /// consumed by P1; ported for signature completeness and to leave the
    /// formula available for the charge-meter follow-up without a second
    /// decomp pass.
    /// </summary>
    public static float GetJumpPower(uint stamina, float burden, bool pk)
    {
        if (pk)
            return stamina / 100.0f - 1.0f;

        return (stamina - 2.0f) / (burden * 8.0f + 4.0f);
    }
}