Add packages/edo for Equal Division of the Octave scales

packages/edo/intervals.mjs

@@ -0,0 +1,103 @@
+/*
+intervals.mjs - defines Intervals for equal division of the octave (EDO) scale
+              - Port of pitfalls/lib/Intervals.lua - see <https://github.com/robmckinnon/pitfalls/blob/main/lib/Intervals.lua>
+Copyright (C) 2025 Rob McKinnon and Strudel contributors - see <https://codeberg.org/uzu/strudel/src/branch/main/packages/edo/intervals.mjs>
+This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details. You should have received a copy of the GNU Affero General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+import ratiointervals from './ratios.mjs';
+
+function ratio(division, edivisions) {
+  return division === 0 ? 1 : Math.pow(2, division / edivisions);
+}
+
+export class Intervals {
+  constructor(scale) {
+    this.scale = scale;
+    this.intLabels = [];
+    this.intNoms = [];
+    this.intRatios = [];
+    this.uniqLabels = [];
+    this.intErrors = [];
+    this.ratios = [];
+
+    const BLANK = '';
+    let division = 0;
+    const labToErr = {};
+    const labToInd = {};
+
+    this.ratios[0] = 1;
+
+    for (let i = 0; i < scale.length; i++) {
+      division += scale.stepValue(i);
+      this.ratios[i + 1] = ratio(division, scale.edivisions);
+
+      if (i < scale.length) {
+        const nearest = ratiointervals.nearestInterval(this.ratios[i + 1]);
+        const closeness = nearest[0];
+        const ratio = nearest[1];
+        const intLabel = ratiointervals.key(ratio);
+        this.intLabels[i + 1] = intLabel;
+        this.intErrors[i + 1] = closeness;
+        this.intNoms[i + 1] = ratio ? ratiointervals.nom(ratio) : 0;
+        this.intRatios[i + 1] = ratio ? `${ratiointervals.nom(ratio)}/${ratiointervals.denom(ratio)}` : '';
+        this.uniqLabels[i + 1] = BLANK;
+
+        if (intLabel && intLabel !== 'P1' && intLabel !== 'P8') {
+          if (!labToErr[intLabel]) {
+            this.uniqLabels[i + 1] = intLabel;
+            labToInd[intLabel] = i + 1;
+            labToErr[intLabel] = closeness;
+          } else if (closeness < labToErr[intLabel]) {
+            this.uniqLabels[labToInd[intLabel]] = BLANK;
+            this.uniqLabels[i + 1] = intLabel;
+            labToInd[intLabel] = i + 1;
+            labToErr[intLabel] = closeness;
+          }
+        }
+      }
+    }
+  }
+
+  ratio(i) {
+    return this.ratios[i];
+  }
+
+  intervalLabel(i) {
+    return this.intLabels[i];
+  }
+
+  intervalNominator(i) {
+    return this.intNoms[i];
+  }
+
+  intervalRatio(i) {
+    return this.intRatios[i];
+  }
+
+  uniqIntervalLabel(i) {
+    return this.uniqLabels[i];
+  }
+
+  intervalError(i) {
+    return this.intErrors[i];
+  }
+
+  nearestDegreeTo(r, threshold) {
+    let min = 1;
+    let degree = null;
+
+    for (const [i, v] of Object.entries(this.ratios)) {
+      const diff = Math.abs((r - v) / r);
+      if (diff < min) {
+        min = diff;
+        degree = parseInt(i, 10);
+      }
+    }
+
+    if (threshold == null) {
+      return degree;
+    } else {
+      return min < threshold ? degree : 1;
+    }
+  }
+}