The Trunk: System-nice.364.mcz

Nicolas Cellier uploaded a new version of System to project The Trunk:
http://source.squeak.org/trunk/System-nice.364.mcz

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

Name: System-nice.364
Author: nice
Time: 28 August 2010, 9:47:42.86 pm
UUID: 4318cbfe-643c-434c-92f6-274f7cfc387e
Ancestors: System-cbc.363

Apply cosmetic refactorings described at http://lists.squeakfoundation.org/pipermail/squeak-dev/2008-July/130162.html
Essentially reuse some existing Integer bit twiddling rather than re-inventing them.

=============== Diff against System-cbc.363 ===============

Item was changed:
  ----- Method: DigitalSignatureAlgorithm>>logOfLargestPowerOfTwoDividing: (in category 'private') -----
  logOfLargestPowerOfTwoDividing: aPositiveInteger
  "Answer the base-2 log of the largest power of two that divides the given integer. For example, the largest power of two that divides 24 is 8, whose log base-2 is 3. Do this efficiently even when the given number is a large integer. Assume that the given integer is > 0."
+ "DigitalSignatureAlgorithm new logOfLargestPowerOfTwoDividing: (32 * 3)"
- "DigitalSignatureAlgorithm new largestPowerOfTwoDividing: (32 * 3)"
 
+ ^aPositiveInteger lowBit - 1!
- | digitIndex power d |
- digitIndex := (1 to: aPositiveInteger digitLength) detect: [:i | (aPositiveInteger digitAt: i) ~= 0].
- power := (digitIndex - 1) * 8.
- d := aPositiveInteger digitAt: digitIndex.
- [d odd] whileFalse: [
- power := power + 1.
- d := d bitShift: -1].
- ^ power
- !

Item was changed:
  ----- Method: ThirtyTwoBitRegister>>leftRotateBy: (in category 'accumulator ops') -----
  leftRotateBy: bits
  "Rotate my contents left by the given number of bits, retaining exactly 32 bits."
  "Details: Perform this operation with as little LargeInteger arithmetic as possible."
 
  | bitCount s1 s2 newHi |
+ "ensure bitCount is in range [0..31]"
- "ensure bitCount is in range [0..32]"
  bitCount := bits \\ 32.
- bitCount < 0 ifTrue: [bitCount := bitCount + 32].
-
  bitCount > 16
  ifTrue: [
  s1 := bitCount - 16.
  s2 := s1 - 16.
  newHi := ((low bitShift: s1) bitAnd: 16rFFFF) bitOr: (hi bitShift: s2).
  low := ((hi bitShift: s1) bitAnd: 16rFFFF) bitOr: (low bitShift: s2).
  hi := newHi]
  ifFalse: [
  s1 := bitCount.
  s2 := s1 - 16.
  newHi := ((hi bitShift: s1) bitAnd: 16rFFFF) bitOr: (low bitShift: s2).
  low := ((low bitShift: s1) bitAnd: 16rFFFF) bitOr: (hi bitShift: s2).
  hi := newHi]
  !

Item was changed:
  ----- Method: DigitalSignatureAlgorithm>>inverseOf:mod: (in category 'large integer arithmetic') -----
  inverseOf: x mod: n
  "Answer the inverse of x modulus n. That is, the integer y such that (x * y) \\ n is 1. Both x and n must be positive, and it is assumed that x < n and that x and n are integers."
  "Details: Use the extended Euclidean algorithm, Schneier, p. 247."
 
+ | v u u1 u2 u3 t1 t2 t3 tmp |
- | v u k u1 u2 u3 t1 t2 t3 tmp |
  ((x <= 0) or: [n <= 0]) ifTrue: [self error: 'x and n must be greater than zero'].
  x >= n ifTrue: [self error: 'x must be < n'].
 
  v := x.
  u := n.
+ (x even and: [n even]) ifTrue: [self error: 'no inverse'].
- k := 0.
- [x even and: [n even and: [u > 0]]] whileTrue: [  "eliminate common factors of two"
- k := k + 1.
- u := u bitShift: -1.
- v := v bitShift: -1].
 
  u1 := 1. u2 := 0. u3 := u.
  t1 := v. t2 := u - 1. t3 := v.
  [ [u3 even ifTrue: [
  ((u1 odd) or: [u2 odd]) ifTrue: [
  u1 := u1 + v.
  u2 := u2 + u].
  u1 := u1 bitShift: -1.
  u2 := u2 bitShift: -1.
  u3 := u3 bitShift: -1].
  ((t3 even) or: [u3 < t3]) ifTrue: [
  tmp := u1. u1 := t1. t1 := tmp.
  tmp := u2. u2 := t2. t2 := tmp.
  tmp := u3. u3 := t3. t3 := tmp].
  u3 even and: [u3 > 0]] whileTrue: ["loop while u3 is even"].
 
  [((u1 < t1) or: [u2 < t2]) and: [u1 > 0]] whileTrue: [
  u1 := u1 + v.
  u2 := u2 + u].
 
  u1 := u1 - t1.
  u2 := u2 - t2.
  u3 := u3 - t3.
  t3 > 0] whileTrue: ["loop while t3 > 0"].
 
  [u1 >= v and: [u2 >= u]] whileTrue: [
  u1 := u1 - v.
  u2 := u2 - u].
 
- u1 := u1 bitShift: k.
- u2 := u2 bitShift: k.
- u3 := u3 bitShift: k.
-
  u3 = 1 ifFalse: [self error: 'no inverse'].
  ^ u - u2
  !

Item was changed:
  ----- Method: DigitalSignatureAlgorithm>>isProbablyPrime: (in category 'large integer arithmetic') -----
  isProbablyPrime: p
  "Answer true if p is prime with very high probability. Such a number is sometimes called an 'industrial grade prime'--a large number that is so extremely likely to be prime that it can assumed that it actually is prime for all practical purposes. This implementation uses the Rabin-Miller algorithm (Schneier, p. 159)."
 
  | iterations factor pMinusOne b m r a j z couldBePrime |
  iterations := 50.  "Note: The DSA spec requires >50 iterations; Schneier says 5 are enough (p. 260)"
 
  "quick elimination: check for p divisible by a small prime"
  SmallPrimes ifNil: [  "generate list of small primes > 2"
  SmallPrimes := Integer primesUpTo: 2000.
  SmallPrimes := SmallPrimes copyFrom: 2 to: SmallPrimes size].
  factor := SmallPrimes detect: [:f | (p \\ f) = 0] ifNone: [nil].
  factor ifNotNil: [^ p = factor].
 
  pMinusOne := p - 1.
  b := self logOfLargestPowerOfTwoDividing: pMinusOne.
+ m := pMinusOne bitShift: b negated.
- m := pMinusOne // (2 raisedTo: b).
  "Assert: pMinusOne = m * (2 raisedTo: b) and m is odd"
 
  Transcript show: '      Prime test pass '.
  r := Random new.
  1 to: iterations do: [:i |
  Transcript show: i printString; space.
  a := (r next * 16rFFFFFF) truncated.
  j := 0.
  z := (a raisedTo: m modulo: p) normalize.
  couldBePrime := z = 1.
  [couldBePrime] whileFalse: [
  z = 1 ifTrue: [Transcript show: 'failed!!'; cr. ^ false].  "not prime"
  z = pMinusOne
  ifTrue: [couldBePrime := true]
  ifFalse: [
  (j := j + 1) < b
  ifTrue: [z := (z * z) \\ p]
  ifFalse: [Transcript show: 'failed!!'; cr. ^ false]]]].  "not prime"
 
  Transcript show: 'passed!!'; cr.
  ^ true  "passed all tests; probably prime"
  !