Nicolas Cellier uploaded a new version of Kernel to project The Trunk:
http://source.squeak.org/trunk/Kernel-nice.262.mcz==================== Summary ====================
Name: Kernel-nice.262
Author: nice
Time: 6 October 2009, 12:21:19 pm
UUID: fbaaa422-359f-3b40-9182-658a0e781350
Ancestors: Kernel-ar.261
Add ANSI required feature #bitAt:
from
http://bugs.squeak.org/view.php?id=6985=============== Diff against Kernel-ar.261 ===============
Item was added:
+ ----- Method: LargePositiveInteger>>bitAt: (in category 'bit manipulation') -----
+ bitAt: anInteger
+ "Optimize super algorithm to avoid long bit operations.
+ Instead work on digits which are known to be SmallInteger and fast.
+ Note that this algorithm does not work for negative integers."
+
+ | digitIndex bitIndex |
+ digitIndex := anInteger - 1 // 8 + 1.
+ digitIndex > self digitLength ifTrue: [^0].
+ bitIndex := anInteger - 1 \\ 8 + 1.
+ ^(self digitAt: digitIndex) bitAt: bitIndex!
Item was added:
+ ----- Method: LargeNegativeInteger>>bitAt: (in category 'bit manipulation') -----
+ bitAt: anInteger
+ "super would not work because we have to pretend we are in two-complement.
+ this has to be tricky..."
+
+ | digitIndex bitIndex i |
+ digitIndex := anInteger - 1 // 8 + 1.
+ digitIndex > self digitLength ifTrue: [^1].
+ bitIndex := anInteger - 1 \\ 8 + 1.
+
+ i := 1.
+ [i = digitIndex
+ ifTrue:
+ ["evaluate two complement (bitInvert + 1) on the digit :
+ (if digitIndex > 1, we must still add 1 due to the carry).
+ but x bitInvert is -1-x, bitInvert+1 is just x negated..."
+ ^(self digitAt: digitIndex) negated bitAt: bitIndex].
+ (self digitAt: i) = 0]
+ whileTrue: [
+ "two complement (bitInvert + 1) raises a carry:
+ 0 bitInvert -> 2r11111111. 2r11111111 + 1 -> 0 with carry...
+ Thus we must inquire one digit forward"
+ i := i + 1].
+
+ "We escaped the while loop, because there is no more carry.
+ Do a simple bitInvert without a carry"
+ ^1 - ((self digitAt: digitIndex) bitAt: bitIndex)!
Item was added:
+ ----- Method: Integer>>bitAt: (in category 'bit manipulation') -----
+ bitAt: anInteger
+ "Answer 1 if the bit at position anInteger is set to 1, 0 otherwise.
+ self is considered an infinite sequence of bits, so anInteger can be any strictly positive integer.
+ Bit at position 1 is the least significant bit.
+ Negative numbers are in two-complements.
+
+ This is a naive implementation that can be refined in subclass for speed"
+
+ ^(self bitShift: 1 - anInteger) bitAnd: 1!
Locked
