Fix bitfield inconsistency after 2 ** 15 (#631)

* Failing tests for large-bitfield inconsistency

* test setting bitfield range with page offset

* fix bitfield setRange offset and remove test

---------

Co-authored-by: Christophe Diederichs <chm-diederichs@protonmail.com>

lib/bitfield.js

@@ -330,14 +330,15 @@ module.exports = class Bitfield {
         p = this._pages.set(i, new BitfieldPage(i, s))
       }
 
-      const last = Math.min(end, BITS_PER_PAGE)
+      const offset = p.index * BITS_PER_PAGE
+      const last = Math.min(end - offset, BITS_PER_PAGE)
       const range = last - j
 
       if (p) p.setRange(j, last, val)
 
       j = 0
       i++
-      end -= range
+      start += range
     }
   }
 

test/bitfield.js

@@ -272,6 +272,25 @@ test('set last bits in segment and findFirst', async function (t) {
   t.is(b.findFirst(false, 2097151), 2097152)
 })
 
+test('bitfield - setRange over multiple pages', async function (t) {
+  const storage = await createStorage(t)
+  const b = await Bitfield.open(storage, 0)
+
+  b.setRange(32768, 32769, true)
+
+  t.is(b.get(0), false)
+  t.is(b.get(32768), true)
+  t.is(b.get(32769), false)
+
+  b.setRange(0, 32768 * 2, false)
+  b.setRange(32768, 32768 * 2 + 1, true)
+
+  t.is(b.get(0), false)
+  t.is(b.get(32768), true)
+  t.is(b.get(32768 * 2), true)
+  t.is(b.get(32768 * 2 + 1), false)
+})
+
 async function createStorage (t, dir) {
   if (!dir) dir = await createTempDir(t)