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The Inbox: Kernel-nice.721.mcz

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The Inbox: Kernel-nice.721.mcz

A new version of Kernel was added to project The Inbox:
http://source.squeak.org/inbox/Kernel-nice.721.mcz

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

Name: Kernel-nice.721
Author: nice
Time: 11 December 2012, 11:28:41.487 pm
UUID: d2b8388c-c225-4fee-aaf6-12e059970915
Ancestors: Kernel-nice.720

Provide an exact version for #floorLog: for Number using exact arithmetic.
Current version is not exact, otherwise this count would be zero:
(-300 to: -1) count: [:n | n ~= ((10 raisedTo: n) floorLog: 10)].

Note however that this won't make #log: exact, and could lead to disagreement between the two functions.

=============== Diff against Kernel-nice.720 ===============

Item was added:
+ ----- Method: Fraction>>floorLog: (in category 'mathematical functions') -----
+ floorLog: radix
+ "Unlike super, this version is exact when radix is integer"
+
+ | d n |
+ radix isInteger ifFalse: [^super floorLog: 10].
+ n := numerator floorLog: radix.
+ d := denominator floorLog: radix.
+ ^(numerator * (radix raisedTo: d))
+ < (denominator * (radix raisedTo: n))
+ ifTrue: [n - d - 1]
+ ifFalse: [n - d]!

Item was added:
+ ----- Method: Integer>>floorLog: (in category 'mathematical functions') -----
+ floorLog: radix
+ "Unlike super, this version is exact when radix is integer"
+
+ radix isInteger ifFalse: [^super floorLog: 10].
+ self <= 0 ifTrue: [^DomainError signal: 'floorLog: is only defined for x > 0.0'].
+ ^(self numberOfDigitsInBase: radix) - 1!

Item was added:
+ ----- Method: ScaledDecimal>>floorLog: (in category 'mathematical functions') -----
+ floorLog: radix
+ "Unlike super, this version is exact when radix is integer"
+
+ ^self asFraction floorLog: radix!

Nicolas Cellier

Re: The Inbox: Kernel-nice.721.mcz

Note: I don't know if it's a good idea to make floorLog: and log:
opinion differ, so the place of such change is the inbox...
However I already did that to aFloat floorLog: 2 which might disagree
with (aFloat log: 2) floor...

An example of failure is (8.0 predecessor floorLog: 2) = (8.0
predecessor log: 2) floor
But you can discover many other with this snippet

| f bad |
bad := OrderedCollection new.
(1 + (Float fminDenormalized floorLog: 2) to: (Float fmax floorLog: 2))
do: [:n |
f := (1.0 timesTwoPower: n) predecessor.
(f floorLog: 2) = (f log: 2) floor ifFalse: [bad add: f].
f := 1.0 timesTwoPower: n.
(f floorLog: 2) = (f log: 2) floor ifFalse: [bad add: f].
f := (1.0 timesTwoPower: n) successor.
(f floorLog: 2) = (f log: 2) floor ifFalse: [bad add: f]].
^bad

2012/12/11 <[hidden email]>:

> A new version of Kernel was added to project The Inbox:
> http://source.squeak.org/inbox/Kernel-nice.721.mcz
>
> ==================== Summary ====================
>
> Name: Kernel-nice.721
> Author: nice
> Time: 11 December 2012, 11:28:41.487 pm
> UUID: d2b8388c-c225-4fee-aaf6-12e059970915
> Ancestors: Kernel-nice.720
>
> Provide an exact version for #floorLog: for Number using exact arithmetic.
> Current version is not exact, otherwise this count would be zero:
> (-300 to: -1) count: [:n | n ~= ((10 raisedTo: n) floorLog: 10)].
>
> Note however that this won't make #log: exact, and could lead to disagreement between the two functions.
>
> =============== Diff against Kernel-nice.720 ===============
>
> Item was added:
> + ----- Method: Fraction>>floorLog: (in category 'mathematical functions') -----
> + floorLog: radix
> + "Unlike super, this version is exact when radix is integer"
> +
> + | d n |
> + radix isInteger ifFalse: [^super floorLog: 10].
> + n := numerator floorLog: radix.
> + d := denominator floorLog: radix.
> + ^(numerator * (radix raisedTo: d))
> + < (denominator * (radix raisedTo: n))
> + ifTrue: [n - d - 1]
> + ifFalse: [n - d]!
>
> Item was added:
> + ----- Method: Integer>>floorLog: (in category 'mathematical functions') -----
> + floorLog: radix
> + "Unlike super, this version is exact when radix is integer"
> +
> + radix isInteger ifFalse: [^super floorLog: 10].
> + self <= 0 ifTrue: [^DomainError signal: 'floorLog: is only defined for x > 0.0'].
> + ^(self numberOfDigitsInBase: radix) - 1!
>
> Item was added:
> + ----- Method: ScaledDecimal>>floorLog: (in category 'mathematical functions') -----
> + floorLog: radix
> + "Unlike super, this version is exact when radix is integer"
> +
> + ^self asFraction floorLog: radix!
>
>