attempt at fastGap, with failing test

strudel.mjs

@@ -426,6 +426,27 @@ class Pattern {
         return patterned
    }
 
+   _fastGap (factor) {
+        // Maybe it's better without this fallback..
+        // if (factor < 1) {
+        //     // there is no gap.. so maybe revert to _fast?
+        //     return this._fast(factor)
+        // }
+        const qf = function(span) { 
+            const cycle = span.begin.sam()
+            const begin = cycle.add(span.begin.sub(span.cycle).mul(factor).min(1))
+            const end   = cycle.add(span.end.sub(span.cycle).mul(factor).min(1))
+            return new TimeSpan(begin, end)
+        }
+        const ef = function(span) { 
+            const cycle = span.begin.sam()
+            const begin = cycle.add(span.begin.sub(span.cycle).div(factor).min(1))
+            const end   = cycle.add(span.end.sub(span.cycle).div(factor).min(1))
+            return new TimeSpan(begin, end)
+        }
+        return this.withQuerySpan(qf).withEventSpan(ef)._splitQueries()
+    }
+
     _fast(factor) {
         const fastQuery = this.withQueryTime(t => t.mul(factor))
         return fastQuery.withEventTime(t => t.div(factor))

test/pattern.test.mjs

@@ -89,6 +89,24 @@ describe('Pattern', function() {
       assert.equal(pure("a")._fast(2).firstCycle.length, 2)
     })
   })
+  describe('_fastGap()', function () {
+    it('Makes things faster, with a gap', function () {
+      assert.deepStrictEqual(
+        sequence("a", "b", "c")._fastGap(2).firstCycle,
+        sequence(["a","b","c"], silence).firstCycle
+      )
+      assert.deepStrictEqual(
+        sequence("a", "b", "c")._fastGap(3).firstCycle,
+        sequence(["a","b","c"], silence, silence).firstCycle
+      )
+    })
+    it('Makes things faster, with a gap, when speeded up further', function () {
+      assert.deepStrictEqual(
+        sequence("a", "b", "c")._fastGap(2).fast(2).firstCycle,
+        sequence(["a","b","c"], silence, ["a","b","c"], silence).firstCycle
+      )
+    })
+  })
   describe('fast()', function () {
     it('Makes things faster', function () {
       assert.equal(pure("a").fast(2).firstCycle.length, 2)