diff --git a/src/FilePositionMap.php b/src/FilePositionMap.php
new file mode 100644
index 0000000..b722100
--- /dev/null
+++ b/src/FilePositionMap.php
@@ -0,0 +1,137 @@
+<?php
+/*---------------------------------------------------------------------------------------------
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+namespace Microsoft\PhpParser;
+
+/**
+ * FilePositionMap can be used to get the line number for a large number of nodes (starting from 1).
+ * It works the most efficiently when the requested node is close to the previously requested node.
+ *
+ * Other designs that weren't chosen:
+ * - Precomputing all of the start/end offsets when initializing was slower - Some offsets weren't needed, and walking the tree was slower.
+ * - Caching line numbers for previously requested offsets wasn't really necessary, since offsets are usually close together and weren't requested repeatedly.
+ */
+class FilePositionMap {
+    /** @var string the full file contents */
+    private $fileContents;
+
+    /** @var int - Precomputed strlen($file_contents) */
+    private $fileContentsLength;
+
+    /** @var int the 0-based byte offset of the most recent request for a line number. */
+    private $currentOffset;
+
+    /** @var int the line number for $this->currentOffset (updated whenever currentOffset is updated) */
+    private $lineForCurrentOffset;
+
+    public function __construct(string $file_contents) {
+        $this->fileContents = $file_contents;
+        $this->fileContentsLength = \strlen($file_contents);
+        $this->currentOffset = 0;
+        $this->lineForCurrentOffset = 1;
+    }
+
+    /**
+     * @param Node $node the node to get the start line for.
+     * TODO deprecate and merge this and getTokenStartLine into getStartLine
+     * if https://github.com/Microsoft/tolerant-php-parser/issues/166 is fixed,
+     * (i.e. if there is a consistent way to get the start offset)
+     */
+    public function getNodeStartLine(Node $node) : int {
+        return $this->getLineNumberForOffset($node->getStart());
+    }
+
+    /**
+     * @param Node $node the node to get the start line for.
+     */
+    public function getTokenStartLine(Token $token) : int {
+        return $this->getLineNumberForOffset($token->start);
+    }
+
+    /**
+     * @param Node|Token $node
+     */
+    public function getStartLine($node) : int {
+        if ($node instanceof Token) {
+            $offset = $node->start;
+        } else {
+            $offset = $node->getStart();
+        }
+        return $this->getLineNumberForOffset($offset);
+    }
+
+    /**
+     * @param Node|Token $node
+     * Similar to getStartLine but includes the column
+     */
+    public function getStartLineCharacterPositionForOffset($node) : LineCharacterPosition {
+        if ($node instanceof Token) {
+            $offset = $node->start;
+        } else {
+            $offset = $node->getStart();
+        }
+        return $this->getLineCharacterPositionForOffset($offset);
+    }
+
+    /** @param Node|Token $node */
+    public function getEndLine($node) : int {
+        return $this->getLineNumberForOffset($node->getEndPosition());
+    }
+
+    /**
+     * @param Node|Token $node
+     * Similar to getStartLine but includes the column
+     */
+    public function getEndLineCharacterPositionForOffset($node) : LineCharacterPosition {
+        return $this->getLineCharacterPositionForOffset($node);
+    }
+
+    /**
+     * @param Node|Token $node
+     * Similar to getStartLine but includes the column
+     */
+    public function getLineCharacterPositionForOffset(int $offset) : LineCharacterPosition {
+        $line = $this->getLineNumberForOffset($offset);
+        $character = $this->getColumnForOffset($offset);
+        return new LineCharacterPosition($line, $character);
+    }
+
+    public function getLineNumberForOffset(int $offset) : int {
+        if ($offset < 0) {
+            $offset = 0;
+        } elseif ($offset > $this->fileContentsLength) {
+            $offset = $this->fileContentsLength;
+        }
+        $currentOffset = $this->currentOffset;
+        if ($offset > $currentOffset) {
+            $this->lineForCurrentOffset += \substr_count($this->fileContents, "\n", $currentOffset, $offset - $currentOffset);
+            $this->currentOffset = $offset;
+        } elseif ($offset < $currentOffset) {
+            $this->lineForCurrentOffset -= \substr_count($this->fileContents, "\n", $offset, $currentOffset - $offset);
+            $this->currentOffset = $offset;
+        }
+        return $this->lineForCurrentOffset;
+    }
+
+    /**
+     * @return int - gets the 1-based column offset
+     */
+    public function getColumnForOffset(int $offset) : int {
+        $length = $this->fileContentsLength;
+        if ($offset <= 1) {
+            return 1;
+        } elseif ($offset > $length) {
+            $offset = $length;
+        }
+        // Postcondition: offset >= 1, ($lastNewlinePos < $offset)
+        // If there was no previous newline, lastNewlinePos = 0
+
+        // Start strrpos check from the character before the current character,
+        // in case the current character is a newline.
+        $lastNewlinePos = \strrpos($this->fileContents, "\n", -$length + $offset - 1);
+        return 1 + $offset - ($lastNewlinePos === false ? 0 : $lastNewlinePos + 1);
+    }
+}
diff --git a/tests/FilePositionMapTest.php b/tests/FilePositionMapTest.php
new file mode 100644
index 0000000..db820a7
--- /dev/null
+++ b/tests/FilePositionMapTest.php
@@ -0,0 +1,54 @@
+<?php
+
+use Microsoft\PhpParser\FilePositionMap;
+use Microsoft\PhpParser\LineCharacterPosition;
+use Microsoft\PhpParser\Node;
+use Microsoft\PhpParser\Token;
+use PHPUnit\Framework\TestCase;
+
+class FilePositionMapTest extends TestCase {
+    public function expectLineCharacterPositionEquals(int $line, int $character, LineCharacterPosition $position) {
+        $this->assertSame($line, $position->line, "Expected same line");
+        $this->assertSame($character, $position->character, "Expected same character");
+    }
+
+    /**
+     * The map keeps the current offset and line -
+     * Move the requests forward, backwards, and to the same position as the previous request to verify that this is done properly.
+     */
+    public function testLineCharacterPosition() {
+        $map = new FilePositionMap("foo\n\nbar\n");
+        $this->expectLineCharacterPositionEquals(1, 1, $map->getLineCharacterPositionForOffset(0));
+        $this->expectLineCharacterPositionEquals(1, 1, $map->getLineCharacterPositionForOffset(-1));
+        $this->expectLineCharacterPositionEquals(1, 3, $map->getLineCharacterPositionForOffset(2));
+        $this->expectLineCharacterPositionEquals(1, 4, $map->getLineCharacterPositionForOffset(3));
+        $this->expectLineCharacterPositionEquals(2, 1, $map->getLineCharacterPositionForOffset(4));
+        $this->expectLineCharacterPositionEquals(1, 4, $map->getLineCharacterPositionForOffset(3));
+        $this->expectLineCharacterPositionEquals(3, 1, $map->getLineCharacterPositionForOffset(5));
+        $this->expectLineCharacterPositionEquals(3, 4, $map->getLineCharacterPositionForOffset(8));
+        $this->expectLineCharacterPositionEquals(3, 4, $map->getLineCharacterPositionForOffset(8));
+        $this->expectLineCharacterPositionEquals(4, 1, $map->getLineCharacterPositionForOffset(9));
+        $this->expectLineCharacterPositionEquals(4, 1, $map->getLineCharacterPositionForOffset(12));
+        $this->expectLineCharacterPositionEquals(1, 4, $map->getLineCharacterPositionForOffset(3));
+    }
+
+    /**
+     * The map keeps the current offset and line -
+     * Move the requests forward, backwards, and to the same position as the previous request to verify that this is done properly.
+     */
+    public function testLineNumber() {
+        $map = new FilePositionMap("foo\n\nbar\n");
+        $this->assertSame(1, $map->getLineNumberForOffset(0));
+        $this->assertSame(1, $map->getLineNumberForOffset(-1));
+        $this->assertSame(1, $map->getLineNumberForOffset(2));
+        $this->assertSame(1, $map->getLineNumberForOffset(3));
+        $this->assertSame(2, $map->getLineNumberForOffset(4));
+        $this->assertSame(3, $map->getLineNumberForOffset(5));
+        $this->assertSame(3, $map->getLineNumberForOffset(8));
+        $this->assertSame(3, $map->getLineNumberForOffset(8));
+        $this->assertSame(4, $map->getLineNumberForOffset(9));
+        $this->assertSame(4, $map->getLineNumberForOffset(12));
+        $this->assertSame(1, $map->getLineNumberForOffset(3));
+        $this->assertSame(2, $map->getLineNumberForOffset(4));
+    }
+}