Adding fromSlice method

Author: chdemko

src/BitArray/BitArray.php

@@ -389,6 +389,73 @@ public static function fromJson($json)
 		return self::fromTraversable(json_decode($json));
 	}
 
+	/**
+	 * Create a new BitArray using a slice
+	 *
+	 * @param   BitArray  $bits    A bitarray to get the slice
+	 * @param   int       $offset  If offset is non-negative, the slice will start at that offset in the bits argument.
+	 *                             If offset is negative, the slice will start that far from the end of the bits argument.
+	 * @param   mixed     $size    If size is given and is positive, then the slice will have up to that many elements in it.
+	 *                             If the bits argument is shorter than the size, then only the available elements will be present.
+	 *                             If size is given and is negative then the slice will stop that many elements from the end of the bits argument.
+	 *                             If it is omitted, then the slice will have everything from offset up until the end of the bits argument.
+	 *
+	 * @return  BitArray  A new BitArray
+	 *
+	 * @since   1.0.0
+	 */
+	public static function fromSlice(BitArray $bits, $offset = 0, $size = null)
+	{
+		$offset = (int) $offset;
+
+		if ($offset < 0)
+		{
+			// Start from the end
+			$offset = $bits->size + $offset;
+
+			if ($offset < 0)
+			{
+				$offset = 0;
+			}
+		}
+		elseif ($offset > $bits->size)
+		{
+			$offset = $bits->size;
+		}
+
+		if ($size === null)
+		{
+			$size = $bits->size - $offset;
+		}
+		else
+		{
+			$size = (int) $size;
+
+			if ($size < 0)
+			{
+				$size = $bits->size + $size - $offset;
+
+				if ($size < 0)
+				{
+					$size = 0;
+				}
+			}
+			elseif ($size > $bits->size - $offset)
+			{
+				$size = $bits->size - $offset;
+			}
+		}
+
+		$slice = new BitArray($size);
+
+		for ($i = 0; $i < $size; $i++)
+		{
+			$slice[$i] = $bits[$i + $offset];
+		}
+
+		return $slice;
+	}
+
 	/**
 	 * Complement the bit array
 	 *

tests/BitArray/BitArrayTest.php

@@ -436,7 +436,7 @@ public function cases_fromString()
 	/**
 	 * Tests  BitArray::fromString
 	 *
-	 * @param   array  $string  Initial values
+	 * @param   string  $string  bits
 	 *
 	 * @return  void
 	 *
@@ -479,6 +479,107 @@ public function test_fromJson()
 		);
 	}
 
+	/**
+	 * Data provider for test_fromSlice
+	 *
+	 * @return  array
+	 *
+	 * @since   1.0.0
+	 */
+	public function cases_fromSlice()
+	{
+		return [
+			['', 0, null, ''],
+			['11010110', 0, null, '11010110'],
+			['11010110', 1, null, '1010110'],
+			['11010110', 8, null, ''],
+			['11010110', 9, null, ''],
+			['11010110', -7, null, '1010110'],
+			['11010110', -8, null, '11010110'],
+			['11010110', -9, null, '11010110'],
+
+			['', 0, 4, ''],
+			['11010110', 0, 4, '1101'],
+			['11010110', 1, 4, '1010'],
+			['11010110', 8, 4, ''],
+			['11010110', 9, 4, ''],
+			['11010110', -7, 4, '1010'],
+			['11010110', -8, 4, '1101'],
+			['11010110', -9, 4, '1101'],
+
+			['', 0, 8, ''],
+			['11010110', 0, 8, '11010110'],
+			['11010110', 1, 8, '1010110'],
+			['11010110', 8, 8, ''],
+			['11010110', 9, 8, ''],
+			['11010110', -7, 8, '1010110'],
+			['11010110', -8, 8, '11010110'],
+			['11010110', -9, 8, '11010110'],
+
+			['', 0, 9, ''],
+			['11010110', 0, 9, '11010110'],
+			['11010110', 1, 9, '1010110'],
+			['11010110', 8, 9, ''],
+			['11010110', 9, 9, ''],
+			['11010110', -7, 9, '1010110'],
+			['11010110', -8, 9, '11010110'],
+			['11010110', -9, 9, '11010110'],
+
+			['', 0, -4, ''],
+			['11010110', 0, -4, '1101'],
+			['11010110', 1, -4, '101'],
+			['11010110', 8, -4, ''],
+			['11010110', 9, -4, ''],
+			['11010110', -7, -4, '101'],
+			['11010110', -8, -4, '1101'],
+			['11010110', -9, -4, '1101'],
+
+			['', 0, -8, ''],
+			['11010110', 0, -8, ''],
+			['11010110', 1, -8, ''],
+			['11010110', 8, -8, ''],
+			['11010110', 9, -8, ''],
+			['11010110', -7, -8, ''],
+			['11010110', -8, -8, ''],
+			['11010110', -9, -8, ''],
+
+			['', 0, -9, ''],
+			['11010110', 0, -9, ''],
+			['11010110', 1, -9, ''],
+			['11010110', 8, -9, ''],
+			['11010110', 9, -9, ''],
+			['11010110', -7, -9, ''],
+			['11010110', -8, -9, ''],
+			['11010110', -9, -9, ''],
+		];
+	}
+
+	/**
+	 * Tests  BitArray::fromSlice
+	 *
+	 * @param   string   $string  Initial values
+	 * @param   integer  $offset  Slice offset
+	 * @param   integer  $size    Slice size
+	 * @param   string   $result  Expected result
+	 *
+	 * @return  void
+	 *
+	 * @covers  chdemko\BitArray\BitArray::fromSlice
+	 * @covers  chdemko\BitArray\BitArray::__construct
+	 * @covers  chdemko\BitArray\BitArray::__toString
+	 *
+	 * @dataProvider  cases_fromSlice
+	 *
+	 * @since   1.0.0
+	 */
+	public function test_fromSlice($string, $offset, $size, $result)
+	{
+		$this->assertEquals(
+			$result,
+			(string) BitArray::fromSlice(BitArray::fromString($string), $offset, $size)
+		);
+	}
+
 	/**
 	 * Tests  BitArray::applyComplement
 	 *