From fbb0f4614ce938aad77eddd6353634b7639fb53e Mon Sep 17 00:00:00 2001
From: Brandon Liu <bdon@bdon.org>
Date: Mon, 19 Sep 2022 21:13:58 -0700
Subject: [PATCH] v3 js: varint routines [#41]

---
 js/index.test.ts | 36 ++++++++++++++++++++++++++----
 js/v3.ts         | 58 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 89 insertions(+), 5 deletions(-)

diff --git a/js/index.test.ts b/js/index.test.ts
index 77fa2bd..7ef451a 100644
--- a/js/index.test.ts
+++ b/js/index.test.ts
@@ -11,7 +11,13 @@ import {
   createDirectory,
 } from "./index";
 
-import { Entry as EntryV3, zxyToTileId, tileIdToZxy, findTile } from "./v3";
+import {
+  Entry as EntryV3,
+  zxyToTileId,
+  tileIdToZxy,
+  findTile,
+  readVarint,
+} from "./v3";
 
 test("stub data", (assertion) => {
   let dataview = createDirectory([
@@ -148,6 +154,22 @@ test("convert spec v1 directory to spec v2 directory", (assertion) => {
   assertion.ok(entry!.offset === 3);
 });
 
+test("varint", (assertion) => {
+  let b: BufferPosition = {
+    buf: new Uint8Array([0, 1, 127, 0xe5, 0x8e, 0x26]),
+    pos: 0,
+  };
+  assertion.eq(readVarint(b), 0);
+  assertion.eq(readVarint(b), 1);
+  assertion.eq(readVarint(b), 127);
+  assertion.eq(readVarint(b), 624485);
+  b = {
+    buf: new Uint8Array([0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x0f]),
+    pos: 0,
+  };
+  assertion.eq(readVarint(b), 9007199254740991);
+});
+
 test("zxy to tile id", (assertion) => {
   assertion.eq(zxyToTileId(0, 0, 0), 0);
   assertion.eq(zxyToTileId(1, 0, 0), 1);
@@ -185,7 +207,9 @@ test("tile search for first entry == id", (assertion) => {
 });
 
 test("tile search for first entry == id", (assertion) => {
-  let entries: EntryV3[] = [{ tileId: 100, offset: 1, length: 1, runLength: 1 }];
+  let entries: EntryV3[] = [
+    { tileId: 100, offset: 1, length: 1, runLength: 1 },
+  ];
   let entry = findTile(entries, 100)!;
   assertion.eq(entry.offset, 1);
   assertion.eq(entry.length, 1);
@@ -193,7 +217,9 @@ test("tile search for first entry == id", (assertion) => {
 });
 
 test("tile search for first entry == id", (assertion) => {
-  let entries: EntryV3[] = [{ tileId: 100, offset: 1, length: 1, runLength: 2 }];
+  let entries: EntryV3[] = [
+    { tileId: 100, offset: 1, length: 1, runLength: 2 },
+  ];
   let entry = findTile(entries, 101)!;
   assertion.eq(entry.offset, 1);
   assertion.eq(entry.length, 1);
@@ -217,7 +243,9 @@ test("tile search for first entry == id", (assertion) => {
 });
 
 test("leaf search", (assertion) => {
-  let entries: EntryV3[] = [{ tileId: 100, offset: 1, length: 1, runLength: 0 }];
+  let entries: EntryV3[] = [
+    { tileId: 100, offset: 1, length: 1, runLength: 0 },
+  ];
   let entry = findTile(entries, 150);
   assertion.eq(entry!.offset, 1);
   assertion.eq(entry!.length, 1);
diff --git a/js/v3.ts b/js/v3.ts
index d4855d6..99b4e39 100644
--- a/js/v3.ts
+++ b/js/v3.ts
@@ -1,3 +1,60 @@
+interface BufferPosition {
+	buf: Uint8Array;
+	pos: number;
+}
+
+function toNum(low: number, high: number): number {
+	return (high >>> 0) * 0x100000000 + (low >>> 0);
+}
+
+function readVarintRemainder(l: number, p: BufferPosition): number {
+	var buf = p.buf,
+		h,
+		b;
+	b = buf[p.pos++];
+	h = (b & 0x70) >> 4;
+	if (b < 0x80) return toNum(l, h);
+	b = buf[p.pos++];
+	h |= (b & 0x7f) << 3;
+	if (b < 0x80) return toNum(l, h);
+	b = buf[p.pos++];
+	h |= (b & 0x7f) << 10;
+	if (b < 0x80) return toNum(l, h);
+	b = buf[p.pos++];
+	h |= (b & 0x7f) << 17;
+	if (b < 0x80) return toNum(l, h);
+	b = buf[p.pos++];
+	h |= (b & 0x7f) << 24;
+	if (b < 0x80) return toNum(l, h);
+	b = buf[p.pos++];
+	h |= (b & 0x01) << 31;
+	if (b < 0x80) return toNum(l, h);
+	throw new Error("Expected varint not more than 10 bytes");
+}
+
+export function readVarint(p: BufferPosition): number {
+	var buf = p.buf,
+		val,
+		b;
+
+	b = buf[p.pos++];
+	val = b & 0x7f;
+	if (b < 0x80) return val;
+	b = buf[p.pos++];
+	val |= (b & 0x7f) << 7;
+	if (b < 0x80) return val;
+	b = buf[p.pos++];
+	val |= (b & 0x7f) << 14;
+	if (b < 0x80) return val;
+	b = buf[p.pos++];
+	val |= (b & 0x7f) << 21;
+	if (b < 0x80) return val;
+	b = buf[p.pos];
+	val |= (b & 0x0f) << 28;
+
+	return readVarintRemainder(val, p);
+}
+
 function rotate(n: number, xy: number[], rx: number, ry: number): void {
 	if (ry == 0) {
 		if (rx == 1) {
@@ -98,4 +155,3 @@ export function findTile(entries: Entry[], tileId: number): Entry | null {
 	}
 	return null;
 }
-