Q-W1 pt2: core/shell/app relocation + sub-namespaces; one concrete ui::Rect (LTRB fork retired); slot_map split from bank_book; BankIndex→BankModel; 59/59 green

src/core/instrument/engine/master_gain.cpp

@@ -0,0 +1,51 @@
+// master_gain.cpp — see master_gain.h. Pure math; no LICE/VST3/REAPER includes.
+
+#include "core/instrument/engine/master_gain.h"
+
+#include "core/util/clamp01.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <limits>
+
+namespace reasampler::instrument::engine {
+
+using util::clamp01;  // the ONE unit-interval clamp (Q-W1, T4-24)
+
+double masterGainMaxLinear() { return std::pow(10.0, kMasterGainMaxDb / 20.0); }
+
+double masterGainDbFromNorm(double norm) {
+    norm = clamp01(norm);
+    if (norm <= 0.0) return -std::numeric_limits<double>::infinity();
+    return kMasterGainMinDb + norm * (kMasterGainMaxDb - kMasterGainMinDb);
+}
+
+double masterGainNormFromDb(double db) {
+    if (!(db > kMasterGainMinDb)) return 0.0;  // -inf, NaN, and the floor all read 0
+    return clamp01((db - kMasterGainMinDb) / (kMasterGainMaxDb - kMasterGainMinDb));
+}
+
+double masterGainLinearFromNorm(double norm) {
+    norm = clamp01(norm);
+    if (norm <= 0.0) return 0.0;  // TRUE silence at the bottom — not an epsilon
+    return std::pow(10.0, masterGainDbFromNorm(norm) / 20.0);
+}
+
+double masterGainNormFromLinear(double linear) {
+    if (!std::isfinite(linear) || linear <= 0.0) return 0.0;
+    return masterGainNormFromDb(20.0 * std::log10(linear));
+}
+
+void formatMasterGainLabel(double norm, char* buf, std::size_t len) {
+    if (!buf || len == 0) return;
+    norm = clamp01(norm);
+    if (norm <= 0.0) {
+        std::snprintf(buf, len, "-inf");
+        return;
+    }
+    const double db = masterGainDbFromNorm(norm);
+    std::snprintf(buf, len, "%+.1fdB", db);
+}
+
+}  // namespace reasampler::instrument::engine