1 files changed, 64 insertions, 0 deletions
diff --git a/vanilla/node_modules/@exodus/bytes/fallback/encoding.util.js b/vanilla/node_modules/@exodus/bytes/fallback/encoding.util.js
new file mode 100644
index 0000000..a53cefb
--- /dev/null
+++ b/vanilla/node_modules/@exodus/bytes/fallback/encoding.util.js
@@ -0,0 +1,64 @@
+// Get a number of last bytes in an Uint8Array `u` ending at `len` that don't
+// form a codepoint yet, but can be a part of a single codepoint on more data
+export function unfinishedBytes(u, len, enc) {
+  switch (enc) {
+    case 'utf-8': {
+      // 0-3
+      let p = 0
+      while (p < 2 && p < len && (u[len - p - 1] & 0xc0) === 0x80) p++ // go back 0-2 trailing bytes
+      if (p === len) return 0 // no space for lead
+      const l = u[len - p - 1]
+      if (l < 0xc2 || l > 0xf4) return 0 // not a lead
+      if (p === 0) return 1 // nothing to recheck, we have only lead, return it. 2-byte must return here
+      if (l < 0xe0 || (l < 0xf0 && p >= 2)) return 0 // 2-byte, or 3-byte or less and we already have 2 trailing
+      const lower = l === 0xf0 ? 0x90 : l === 0xe0 ? 0xa0 : 0x80
+      const upper = l === 0xf4 ? 0x8f : l === 0xed ? 0x9f : 0xbf
+      const n = u[len - p]
+      return n >= lower && n <= upper ? p + 1 : 0
+    }
+
+    case 'utf-16le':
+    case 'utf-16be': {
+      // 0-3
+      const p = len % 2 // uneven byte length adds 1
+      if (len < 2) return p
+      const l = len - p - 1
+      const last = enc === 'utf-16le' ? (u[l] << 8) ^ u[l - 1] : (u[l - 1] << 8) ^ u[l]
+      return last >= 0xd8_00 && last < 0xdc_00 ? p + 2 : p // lone lead adds 2
+    }
+  }
+
+  throw new Error('Unsupported encoding')
+}
+
+// Merge prefix `chunk` with `u` and return new combined prefix
+// For u.length < 3, fully consumes u and can return unfinished data,
+// otherwise returns a prefix with no unfinished bytes
+export function mergePrefix(u, chunk, enc) {
+  if (u.length === 0) return chunk
+  if (u.length < 3) {
+    // No reason to bruteforce offsets, also it's possible this doesn't yet end the sequence
+    const a = new Uint8Array(u.length + chunk.length)
+    a.set(chunk)
+    a.set(u, chunk.length)
+    return a
+  }
+
+  // Slice off a small portion of u into prefix chunk so we can decode them separately without extending array size
+  const t = new Uint8Array(chunk.length + 3) // We have 1-3 bytes and need 1-3 more bytes
+  t.set(chunk)
+  t.set(u.subarray(0, 3), chunk.length)
+
+  // Stop at the first offset where unfinished bytes reaches 0 or fits into u
+  // If that doesn't happen (u too short), just concat chunk and u completely (above)
+  for (let i = 1; i <= 3; i++) {
+    const unfinished = unfinishedBytes(t, chunk.length + i, enc) // 0-3
+    if (unfinished <= i) {
+      // Always reachable at 3, but we still need 'unfinished' value for it
+      const add = i - unfinished // 0-3
+      return add > 0 ? t.subarray(0, chunk.length + add) : chunk
+    }
+  }
+
+  // Unreachable
+}