# [Pkg] The Trunk: Collections-nice.829.mcz

commits at source.squeak.org commits at source.squeak.org
Fri May 3 21:06:20 UTC 2019

```Nicolas Cellier uploaded a new version of Collections to project The Trunk:
http://source.squeak.org/trunk/Collections-nice.829.mcz

==================== Summary ====================

Name: Collections-nice.829
Author: nice
Time: 3 May 2019, 11:06:11.65639 pm
UUID: 695419ed-754d-41ff-8b51-b8715934b1f5
Ancestors: Collections-fn.828

Remove unused digitShiftSum: (since Kernel-nice.1224)

=============== Diff against Collections-fn.828 ===============

Item was removed:
- ----- Method: Interval>>digitShiftSum: (in category 'enumerating') -----
- digitShiftSum: aBlock
- 	"Reconstruct an Integer that has been split in chunks by using shift and add.
- 	Each of my element represent a digitShift, an my step size repreent the digit length of chunks.
- 	The block is evaluated with each digitShift to produce the chunks.
-
- 	Algorithm insights:
- 	Let d0,d1,d2,... be the chunks, and s be the bit shift (8*step because digitLength is 8bits)
- 	The naive loop does shift each chunk and accumulate into a sum:
- 		((d0 + (d1<<s)) + (d2<<s)) + (d3<<s) + ...
- 	The length of accumulator increase at each iteration (1+2+3...) resulting in a cost (size+1)*size/2, or O(size^2)
- 	Note that Horner scheme would be of about same cost
- 		(((... + d3) << s + d2) << s + d1) << s + d0
-     	(a bit like so called Shlemiel the painter)
- 	If we instead divide and conquer, we add smaller parts (1+1+2+...) resulting into a cost of O(size*log2(size))
- 		(d0 + (d1<<s)) + ((d2 + (d3<<s)) << s) + ...
- 	However, the divide and conquer split comes with an additionnal cost, so do it only if worth it."
-
-     | sz half offset |
- "Naive loop in O(size^2)/2 is best for small size"
-     (sz := self size) <= 8 ifTrue: [^self inject: 0 into: [:sum :shift | ((aBlock value: shift) bitShift: 8 * shift) + sum]].
-     half := sz // 2.
-     offset := half * step + start.
-     ^((start to: half - 1 * step + start by: step) digitShiftSum: aBlock)
-         + (((0 to: self last - offset by: step) digitShiftSum: [:k | aBlock value: offset + k]) bitShift: 8 * offset)!

```