Speed up rotating square images by 90 or 270 degrees

[radarhere]

rotate() may use transpose() for a faster result. For 90 or 270 degrees, it makes sure that the expand is true, since rotating an image sideways may change the size... except if the image is a square, so I've created this PR.

The test does not fail without this change, since this is just a speed improvement.

Pillow/src/PIL/Image.py

Lines 2070 to 2080 in 6cb127c

	# Fast paths regardless of filter, as long as we're not
	# translating or changing the center.
	if not (center or translate):
	if angle == 0:
	return self.copy()
	if angle == 180:
	return self.transpose(ROTATE_180)
	if angle == 90 and expand:
	return self.transpose(ROTATE_90)
	if angle == 270 and expand:
	return self.transpose(ROTATE_270)

[hugovk]

What sort of speed increase does this give?

[radarhere]

import timeit
setup = '''
from PIL import Image
im = Image.open("Tests/images/hopper.png")
'''
print(timeit.Timer('im.rotate(90)', setup=setup).repeat(number=10000))

# Without change: [0.23164604200000002, 0.23040333300000004, 0.22858733399999998, 0.22947383300000002, 0.228850459]
# With change: [0.10277529199999999, 0.10330620800000001, 0.10458945799999997, 0.10447408300000005, 0.10545916600000005]

So it makes it twice as fast.

[homm]

It will be much more significant for larger images.

[hugovk]

Thanks, this is worth including in the release notes as well.