Enhancement Request: Adding population count for Integers to
the standard image
Richard A. O'Keefe
ok at cs.otago.ac.nz
Thu Dec 9 01:13:20 UTC 2004
"Matthew Hamrick" <Matthew.Hamrick at gibson.com> wrote
(edited somewhat to take fewer lines and be more ASCII-friendly):
"Answers the number of bits set in an integer."
| t1 t2 |
t1 := self.
t2 := 0.
[t1 == 0] whileFalse: [t1 := t1 bitAnd: t1 - 1. t2 := t2 + 1].
What is this supposed to do when the number is negative?
-1 bitAnd: -2 => -2
-2 bitAnd: -3 => -4
-4 bitAnd: -5 => -8
In Squeak 3.6-5429-full.image, (-1 popCount) eventually terminates because
m := -1 bitShift: 31.
m := m bitAnd: m - 1
sets m to 0, instead of to the correct value (-1 bitShift: 32).
First time I've ever had Squeak give me the wrong answer for an
Notionally, a Squeak negative integer has infinitely many 1 bits, so I
"self >= 0 => answer the number of 1 bits in the binary representation.
self < 0 => answer the number of 0 bits in the binary representation.
Two's complement is assumed.
(m := self) < 0 ifTrue: [m := -1 - self].
n := 0.
[m == 0] whileFalse: [m := m bitAnd: m-1. n := n+1].
Another alternative would be to make it an error to send #popCount to a
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