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CWE-ou-minkata/Sources/Plasma/NucleusLib/pnUtils/Private/pnUtBigNum.cpp

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/*==LICENSE==*
CyanWorlds.com Engine - MMOG client, server and tools
Copyright (C) 2011 Cyan Worlds, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
You can contact Cyan Worlds, Inc. by email legal@cyan.com
or by snail mail at:
Cyan Worlds, Inc.
14617 N Newport Hwy
Mead, WA 99021
*==LICENSE==*/
/*****************************************************************************
*
* $/Plasma20/Sources/Plasma/NucleusLib/pnUtils/Private/pnUtBigNum.cpp
*
***/
#include "../Pch.h"
#pragma hdrstop
/****************************************************************************
*
* Constants and macros
*
***/
const unsigned VAL_BITS = 8 * sizeof(BigNum::Val);
const BigNum::DVal VAL_RANGE = ((BigNum::DVal)1) << VAL_BITS;
#define LOW(dval) ((Val)(dval))
#define HIGH(dval) ((Val)((dval) / VAL_RANGE))
#define PACK(low, high) ((DVal)((high) * VAL_RANGE + (low)))
#define ALLOC_TEMP(struct, count) \
(struct).UseTempAlloc((Val *)_alloca((count) * sizeof(Val)), count)
/****************************************************************************
*
* BigNum private methods
*
***/
//===========================================================================
void BigNum::SetVal (unsigned index, Val value) {
ARRAY(Val)::operator[](index) = value;
}
//===========================================================================
void BigNum::SetVal (unsigned index, DVal value, Val * carry) {
ARRAY(Val)::operator[](index) = LOW(value);
*carry = HIGH(value);
}
//===========================================================================
void BigNum::Trim (unsigned count) {
ASSERT(count <= Count());
while (count && !ARRAY(Val)::operator[](count - 1))
--count;
SetCountFewer(count);
}
//===========================================================================
BigNum * BigNum::UseTempAlloc (Val * ptr, unsigned count) {
m_isTemp = true;
AttachTemp(ptr, count);
return this;
}
/****************************************************************************
*
* BigNum public methods
*
***/
//===========================================================================
BigNum::BigNum () :
m_isTemp(false)
{
}
//===========================================================================
BigNum::BigNum (const BigNum & a) :
m_isTemp(false)
{
Set(a);
}
//===========================================================================
BigNum::BigNum (unsigned a) :
m_isTemp(false)
{
Set(a);
}
//===========================================================================
BigNum::BigNum (unsigned bytes, const void * data) :
m_isTemp(false)
{
FromData(bytes, data);
}
//===========================================================================
BigNum::BigNum (const wchar str[], Val radix) :
m_isTemp(false)
{
FromStr(str, radix);
}
//===========================================================================
BigNum::~BigNum () {
if (m_isTemp)
Detach();
}
//===========================================================================
void BigNum::Add (const BigNum & a, Val b) {
// this = a + b
const unsigned count = a.Count();
GrowToCount(count + 1, true);
unsigned index = 0;
Val carry = b;
for (; index < count; ++index)
SetVal(index, (DVal)((DVal)a[index] + (DVal)carry), &carry);
if (carry)
SetVal(index++, carry);
Trim(index);
}
//===========================================================================
void BigNum::Add (const BigNum & a, const BigNum & b) {
// this = a + b
const unsigned aCount = a.Count();
const unsigned bCount = b.Count();
const unsigned count = aCount + bCount;
GrowToCount(count + 1, true);
unsigned index = 0;
Val carry = 0;
for (; index < count; ++index) {
Val aVal = (index < aCount) ? a[index] : (Val)0;
Val bVal = (index < bCount) ? b[index] : (Val)0;
SetVal(index, (DVal)((DVal)aVal + (DVal)bVal + (DVal)carry), &carry);
}
if (carry)
SetVal(index++, carry);
Trim(index);
}
//===========================================================================
int BigNum::Compare (Val a) const {
// -1 if (this < a)
// 0 if (this == a)
// 1 if (this > a)
// Handle the case where this number has more digits than the comparand
const unsigned count = Count();
ASSERT(!count || (*this)[count - 1]);
if (count > 1)
return 1;
// Handle the case where this number has fewer digits than the comparand
if (!count)
return a ? -1 : 0;
// Handle the case where both numbers share the same number of digits
Val thisVal = (*this)[0];
return (thisVal > a) ? 1 : (thisVal < a) ? -1 : 0;
}
//===========================================================================
int BigNum::Compare (const BigNum & a) const {
// -1 if (this < a)
// 0 if (this == a)
// 1 if (this > a)
// Handle the case where this number has more digits than the comparand
const unsigned thisCount = Count();
const unsigned compCount = a.Count();
ASSERT(!thisCount || (*this)[thisCount - 1]);
ASSERT(!compCount || a[compCount - 1]);
if (thisCount > compCount)
return 1;
// Handle the case where this number has fewer digits than the comparand
if (thisCount < compCount)
return -1;
// Handle the case where both numbers share the same number of digits
for (unsigned index = thisCount; index--; ) {
Val thisVal = (*this)[index];
Val compVal = a[index];
if (thisVal == compVal)
continue;
return (thisVal > compVal) ? 1 : -1;
}
return 0;
}
//===========================================================================
void BigNum::Div (const BigNum & a, Val b, Val * remainder) {
// this = a / b, remainder = a % b
const unsigned count = a.Count();
SetCount(count);
*remainder = 0;
for (unsigned index = count; index--; ) {
DVal value = PACK(a[index], *remainder);
SetVal(index, (Val)(value / b));
*remainder = (Val)(value % b);
}
Trim(count);
}
//===========================================================================
void BigNum::Div (const BigNum & a, const BigNum & b, BigNum * remainder) {
// this = a / b, remainder = a % b
// either this or remainder may be nil
ASSERT(this != remainder);
// Check for division by zero
ASSERT(b.Count() && b[b.Count() - 1]);
// Normalize the operands so that the highest bit is set in the most
// significant word of the denominator
const unsigned shift = 8 * sizeof(Val) - MathHighBitPos(b[b.Count() - 1]) - 1;
BigNum aaBuffer;
BigNum bbBuffer;
BigNum * aa = shift ? ALLOC_TEMP(aaBuffer, a.Count() + 1) : (BigNum *)&a;
BigNum * bb = shift ? ALLOC_TEMP(bbBuffer, b.Count() + 1) : (BigNum *)&b;
if (shift) {
aa->Shl(a, shift);
bb->Shl(b, shift);
}
// Perform the division
DivNormalized(*aa, *bb, remainder);
// Denormalize the remainder
if (remainder)
remainder->Shr(*remainder, shift);
}
//===========================================================================
void BigNum::DivNormalized (const BigNum & a, const BigNum & b, BigNum * remainder) {
// this = a / b, remainder = a % b
// either this or remainder may be nil
// high bit of b must be set
ASSERT(this != remainder);
// Check for division by zero
ASSERT(b.Count() && b[b.Count() - 1]);
// Verify that the operands are normalized
ASSERT(MathHighBitPos(b[b.Count() - 1]) == 8 * sizeof(Val) - 1);
// Handle the case where the denominator is greater than the numerator
if ((b.Count() > a.Count()) || (b.Compare(a) > 0)) {
if (remainder && (remainder != &a))
remainder->Set(a);
if (this)
ZeroCount();
return;
}
// Create a distinct buffer for the denominator if necessary
BigNum denomTemp;
BigNum * denom = ((&b != this) && (&b != remainder)) ? (BigNum *)&b : ALLOC_TEMP(denomTemp, b.Count());
denom->Set(b);
// Store the numerator into the remainder buffer
BigNum numerTemp;
BigNum * numer = remainder ? remainder : ALLOC_TEMP(numerTemp, a.Count());
numer->Set(a);
// Prepare the destination buffer
const unsigned numerCount = numer->Count();
const unsigned denomCount = denom->Count();
if (this)
this->SetCount(numerCount + 1 - denomCount);
// Calculate the quotient one word at a time
DVal t = (DVal)((DVal)(*denom)[denomCount - 1] + (DVal)1);
for (unsigned quotientIndex = numerCount + 1 - denomCount; quotientIndex--; ) {
// Calculate the approximate value of the next quotient word,
// erring on the side of underestimation
Val low = (*numer)[quotientIndex + denomCount - 1];
Val high = (quotientIndex + denomCount < numerCount) ? (*numer)[quotientIndex + denomCount] : (Val)0;
ASSERT(high < t);
Val quotient = (Val)(PACK(low, high) / t);
// Calculate the product of the denominator and this quotient word
// (using zero for all lower quotient words) and subtract the product
// from the current numerator
if (quotient) {
Val borrow = 0;
Val carry = 0;
unsigned denomIndex;
for (denomIndex = 0; denomIndex != denomCount; ++denomIndex) {
DVal product = (DVal)(Mul((*denom)[denomIndex], quotient) + carry);
carry = HIGH(product);
numer->SetVal(quotientIndex + denomIndex, (DVal)((DVal)(*numer)[quotientIndex + denomIndex] - (DVal)LOW(product) - (DVal)borrow), &borrow);
borrow = (Val)((Val)0 - (Val)borrow);
}
if (quotientIndex + denomCount != numerCount) {
numer->SetVal(quotientIndex + denomCount, (DVal)((DVal)(*numer)[quotientIndex + denomIndex] - (DVal)carry - (DVal)borrow), &borrow);
carry = 0;
}
ASSERT(!carry);
ASSERT(!borrow);
}
// Check whether we underestimated the quotient word, and adjust
// it if necessary
for (;;) {
// Test whether the current numerator is still greater than or
// equal to the denominator
if ((quotientIndex + denomCount == numerCount) || !(*numer)[quotientIndex + denomCount]) {
bool numerLess = false;
for (unsigned denomIndex = denomCount; !numerLess && denomIndex--; ) {
Val numerVal = (*numer)[quotientIndex + denomIndex];
Val denomVal = (*denom)[denomIndex];
numerLess = (numerVal < denomVal);
if (numerVal != denomVal)
break;
}
if (numerLess)
break;
}
// Increment the quotient by one, and correct the current
// numerator for this adjustment by subtracting the denominator
++quotient;
Val borrow = 0;
for (unsigned denomIndex = 0; denomIndex != denomCount; ++denomIndex) {
numer->SetVal(quotientIndex + denomIndex, (DVal)((DVal)(*numer)[quotientIndex + denomIndex] - (DVal)(*denom)[denomIndex] - (DVal)borrow), &borrow);
borrow = (Val)((Val)0 - (Val)borrow);
}
if (borrow)
numer->SetVal(quotientIndex + denomCount, (DVal)((DVal)(*numer)[quotientIndex + denomCount] - (DVal)borrow), &borrow);
ASSERT(!borrow);
}
ASSERT((quotientIndex + denomCount == numerCount) || !(*numer)[quotientIndex + denomCount]);
// Store the final quotient word
if (this)
this->SetVal(quotientIndex, quotient);
}
// The final remainder is the remaining portion of the numerator
if (remainder) {
ASSERT(remainder == numer);
remainder->Trim(denomCount);
}
// Trim the result
if (this)
this->Trim(numerCount + 1 - denomCount);
}
//===========================================================================
void BigNum::FromData (unsigned bytes, const void * data) {
ASSERT(data || !bytes);
// Calculate the number of words required to hold the data
unsigned count = (bytes + sizeof(Val) - 1) / sizeof(Val);
SetCount(count);
// Fill in whole words
unsigned index = 0;
unsigned offset = 0;
for (; offset + sizeof(Val) <= bytes; ++index, offset += sizeof(Val))
SetVal(index, *(const Val *)((const byte *)data + offset));
// Fill in the final partial word
if (offset < bytes) {
Val value = 0;
MemCopy(&value, (const byte *)data + offset, bytes - offset);
SetVal(index, value);
}
}
//===========================================================================
void BigNum::FromStr (const wchar str[], Val radix) {
ASSERT(str);
// Decode the prefix
if (str[0] == L'0') {
if ((str[1] == L'x') || (str[1] == L'X')) {
str += 2;
if (!radix)
radix = 16;
}
else if ((str[1] >= L'0') && (str[1] <= L'9')) {
str += 1;
if (!radix)
radix = 8;
}
else if (!radix) {
ZeroCount();
return;
}
}
else if (!radix)
radix = 10;
// Decode the number
ZeroCount();
for (; *str; ++str) {
// Decode the next character
Val value;
if ((*str >= L'0') && (*str <= '9'))
value = (Val)(*str - L'0');
else if ((*str >= L'a') && (*str <= L'z'))
value = (Val)(*str + 10 - L'a');
else if ((*str >= L'A') && (*str <= L'Z'))
value = (Val)(*str + 10 - L'A');
else
break;
if (value >= radix)
break;
// Apply it to the result
Mul(*this, radix);
Add(*this, value);
}
}
//===========================================================================
void BigNum::Gcd (const BigNum & a, const BigNum & b) {
// Allocate working copies of a and b
BigNum aa;
BigNum bb;
unsigned maxCount = max(a.Count(), b.Count());
ALLOC_TEMP(aa, maxCount + 1);
ALLOC_TEMP(bb, maxCount + 1);
aa.Set(a);
bb.Set(b);
// Find the greatest common denominator using Euclid's algorithm
Set(bb);
while (aa.Count()) {
Set(aa);
aa.Mod(bb, aa);
bb.Set(*this);
}
}
//===========================================================================
const void * BigNum::GetData (unsigned * bytes) const {
if (bytes)
*bytes = Bytes();
return Ptr();
}
//===========================================================================
unsigned BigNum::HighBitPos () const {
// returns the position of the highest set bit, or -1 if no bits are set
for (unsigned index = Count(); index--; ) {
Val val = (*this)[index];
if (!val)
continue;
return index * 8 * sizeof(Val) + MathHighBitPos(val);
}
return (unsigned)-1;
}
//===========================================================================
bool BigNum::InverseMod (const BigNum & a, const BigNum & b) {
// finds value for this such that (a ^ -1) == (this mod b)
// returns false if a has no inverse modulo b
// Verify that a and b are nonzero
ASSERT(a.Count());
ASSERT(b.Count());
// Verify that a is less than b
ASSERT(a.Compare(b) < 0);
// Verify that either a or b is odd. If both are even then they cannot
// possibly be relatively prime, so there cannot be a solution.
if (!(a.IsOdd() || b.IsOdd()))
return false;
// Allocate buffers for intermediate values
BigNum uArray[3];
BigNum tArray[3];
BigNum * u = uArray;
BigNum * t = tArray;
// Find the inverse using the extended Euclidean algorithm
u[0].SetOne();
u[1].SetZero();
u[2].Set(b);
t[0].Set(a);
t[1].Sub(b, 1);
t[2].Set(a);
do {
do {
if (!u[2].IsOdd()) {
if (u[0].IsOdd() || u[1].IsOdd()) {
u[0].Add(u[0], a);
u[1].Add(u[1], b);
}
u[0].Shr(u[0], 1);
u[1].Shr(u[1], 1);
u[2].Shr(u[2], 1);
}
if (!t[2].IsOdd() || (u[2].Compare(t[2]) < 0))
SWAP(u, t);
} while (!u[2].IsOdd());
while ((u[0].Compare(t[0]) < 0) || (u[1].Compare(t[1]) < 0)) {
u[0].Add(u[0], a);
u[1].Add(u[1], b);
}
u[0].Sub(u[0], t[0]);
u[1].Sub(u[1], t[1]);
u[2].Sub(u[2], t[2]);
} while (t[2].Count());
while ((u[0].Compare(a) >= 0) && (u[1].Compare(b) >= 0)) {
u[0].Sub(u[0], a);
u[1].Sub(u[1], b);
}
// If the greatest common denominator is not one then there is no
// solution
if (u[2].Compare(1))
return false;
// Return the solution
Sub(b, u[1]);
return true;
}
//===========================================================================
bool BigNum::IsMultiple (Val a) const {
// returns true if (this % a) == 0
DVal remainder = 0;
for (unsigned index = Count(); index--; )
remainder = (DVal)(PACK((*this)[index], remainder) % a);
return !remainder;
}
//===========================================================================
bool BigNum::IsOdd () const {
// returns true if this is an odd number
return Count() ? (*this)[0] & 1 : false;
}
//===========================================================================
bool BigNum::IsPrime () const {
// returns true if there is a strong likelihood that this is prime
// Verify that the number is odd, or is exactly equal to two
if (!Count() || (!((*this)[0] & 1) && ((Count() > 1) || ((*this)[0] > 2))))
return false;
// Verify that the number is not evenly divisible by a small prime
static const Val smallPrimes[] = {3, 5, 7, 11};
unsigned loop;
for (loop = 0; loop != arrsize(smallPrimes); ++loop)
if (IsMultiple(smallPrimes[loop]))
return false;
if (Compare(smallPrimes[arrsize(smallPrimes)-1]) <= 0)
return true;
// Rabin-Miller Test
// Calculate b, where b is the number of times 2 divides (this - 1)
BigNum this_1;
ALLOC_TEMP(this_1, Count());
this_1.Sub(*this, 1);
const unsigned b = this_1.LowBitPos();
// Calculate m, such that this == 1 + 2 ^ b * m
BigNum m;
ALLOC_TEMP(m, Count());
m.Shr(this_1, b);
// For a number of witnesses, test whether the witness demonstrates this
// number to be composite via Fermat's Little Theorem, or has a
// nontrivial square root mod n
static const Val witnesses[] = {3, 5, 7};
BigNum z;
ALLOC_TEMP(z, 2 * (Count() + 1));
for (loop = 0; loop != arrsize(witnesses); ++loop) {
// Initialize z to (witness ^ m % this)
z.PowMod(witnesses[loop], m, *this);
// This passes the test if (z == 1)
if (!z.Compare(1))
continue;
for (unsigned j = 0; z.Compare(this_1); ) {
// This fails the test if we reach b iterations.
++j;
if (j == b)
return false;
// Square z. This fails the test if z mod this equals 1.
z.MulMod(z, z, *this);
if (!z.Compare(1))
return false;
}
}
return true;
}
//===========================================================================
unsigned BigNum::LowBitPos () const {
// returns the position of the lowest set bit, or -1 if no bits are set
for (unsigned index = 0, count = Count(); index < count; ++index) {
Val val = (*this)[index];
if (!val)
continue;
for (unsigned bit = 0; ; ++bit)
if (val & (1 << bit))
return index * 8 * sizeof(Val) + bit;
}
return (unsigned)-1;
}
//===========================================================================
void BigNum::Mod (const BigNum & a, const BigNum & b) {
// this = a % b
((BigNum *)nil)->Div(a, b, this);
}
//===========================================================================
void BigNum::ModNormalized (const BigNum & a, const BigNum & b) {
// this = a % b
// high bit of b must be set
((BigNum *)nil)->DivNormalized(a, b, this);
}
//===========================================================================
BigNum::DVal BigNum::Mul (BigNum::Val a, BigNum::Val b) {
// returns a * b
return (DVal)a * (DVal)b;
}
//===========================================================================
void BigNum::Mul (const BigNum & a, Val b) {
// this = a * b
const unsigned count = a.Count();
GrowToCount(count + 1, true);
unsigned index = 0;
Val carry = 0;
for (; index < count; ++index)
SetVal(index, (DVal)(Mul(a[index], b) + carry), &carry);
if (carry)
SetVal(index++, carry);
Trim(index);
}
//===========================================================================
void BigNum::Mul (const BigNum & a, const BigNum & b) {
// this = a * b
const unsigned aCount = a.Count();
const unsigned bCount = b.Count();
const unsigned count = aCount + bCount;
SetCount(count);
if (!count)
return;
// We perform the multiplication from left to right, so that we don't
// overwrite any operand words before they're used in the case that
// the destination is not distinct from either of the operands
SetVal(count - 1, 0);
for (unsigned index = count - 1; index--; ) {
// Iterate every combination of aIndex + bIndex that adds up to
// index, and sum the products of those words
DVal value = 0;
const unsigned aStart = (index < bCount) ? 0 : (index + 1 - bCount);
const unsigned aTerm = min(index + 1, aCount);
for (unsigned aIndex = aStart; aIndex != aTerm; ++aIndex) {
// Accumulate the product of this pair of words
value = (DVal)(Mul(a[aIndex], b[index - aIndex]) + value);
// If the product exceeds the word size, apply carry
Val carry = HIGH(value);
for (unsigned carryIndex = index + 1; carry; ++carryIndex)
SetVal(carryIndex, (DVal)((DVal)(*this)[carryIndex] + (DVal)carry), &carry);
value = LOW(value);
}
// Store the sum of products as the final value for index
SetVal(index, LOW(value));
}
Trim(count);
}
//===========================================================================
void BigNum::MulMod (const BigNum & a, const BigNum & b, const BigNum & c) {
// this = a * b % c
if (this != &c) {
Mul(a, b);
Mod(*this, c);
}
else {
BigNum temp;
ALLOC_TEMP(temp, a.Count() + b.Count());
temp.Mul(a, b);
Mod(temp, c);
}
}
//===========================================================================
void BigNum::PowMod (Val a, const BigNum & b, const BigNum & c) {
// this = a ^ b % c
// Verify that b is distinct from this
BigNum bbBuffer;
const BigNum & bb = (&b != this) ? b : bbBuffer;
if (&bb != &b) {
ALLOC_TEMP(bbBuffer, b.Count());
bbBuffer.Set(b);
}
// Generate a table which may allow us to process two bits at once
Val aMult[4] = {
1,
a,
(Val)(a * a),
(Val)(a * a * a)
};
bool overflow = (aMult[2] < a) || (aMult[3] < a) || (c.Compare(aMult[3]) <= 0);
// Normalize the denominator so that the high bit is set. The result
// will be built shifted an equivalent amount.
const unsigned shift = 8 * sizeof(Val) - MathHighBitPos(c[c.Count() - 1]) - 1;
BigNum cc;
ALLOC_TEMP(cc, c.Count() + 1);
cc.Shl(c, shift);
// Perform the exponentiation from left to right two bits at a time
if (!overflow) {
SetBits(shift, 1);
bool anySet = false;
for (unsigned index = bb.Count(); index--; )
for (unsigned bit = 8 * sizeof(Val); bit; ) {
bit -= 2;
if (anySet) {
Square(*this);
Shr(*this, shift);
ModNormalized(*this, cc);
Square(*this);
Shr(*this, shift);
ModNormalized(*this, cc);
}
unsigned entry = (bb[index] >> bit) & 3;
if (entry) {
Mul(*this, aMult[entry]);
ModNormalized(*this, cc);
anySet = true;
}
}
}
// Perform the exponentiation from left to right a single bit at a time
else {
SetBits(shift, 1);
bool anySet = false;
for (unsigned index = bb.Count(); index--; )
for (unsigned bit = 8 * sizeof(Val); bit--; ) {
if (anySet) {
Square(*this);
ModNormalized(*this, cc);
}
if (bb[index] & (1 << bit)) {
Mul(*this, a);
ModNormalized(*this, cc);
anySet = true;
}
}
}
// Denormalize the result
Shr(*this, shift);
}
//===========================================================================
void BigNum::PowMod (const BigNum & a, const BigNum & b, const BigNum & c) {
// this = a ^ b % c
// Verify that a and b are distinct from this
BigNum distinctTemp;
const BigNum & aa = (&a != this) ? a : distinctTemp;
const BigNum & bb = (&b != this) ? b : distinctTemp;
if ((&aa != &a) || (&bb != &b)) {
ALLOC_TEMP(distinctTemp, Count());
distinctTemp.Set(*this);
}
// Generate a table which will allow us to process two bits at once
BigNum a2;
BigNum a3;
ALLOC_TEMP(a2, 2 * aa.Count() + 1);
ALLOC_TEMP(a3, 3 * aa.Count() + 1);
a2.Mul(aa, aa);
a2.Mod(a2, c);
a3.Mul(aa, a2);
a3.Mod(a3, c);
const BigNum * aMult[] = {
nil,
&aa,
&a2,
&a3
};
// Normalize the denominator so that the high bit is set. The result
// will be built shifted an equivalent amount.
const unsigned shift = 8 * sizeof(Val) - MathHighBitPos(c[c.Count() - 1]) - 1;
BigNum cc;
ALLOC_TEMP(cc, c.Count() + 1);
cc.Shl(c, shift);
// Perform the exponentiation from left to right two bits at a time
SetBits(shift, 1);
bool anySet = false;
for (unsigned index = bb.Count(); index--; )
for (unsigned bit = 8 * sizeof(Val); bit; ) {
bit -= 2;
if (anySet) {
Square(*this);
Shr(*this, shift);
ModNormalized(*this, cc);
Square(*this);
Shr(*this, shift);
ModNormalized(*this, cc);
}
unsigned entry = (bb[index] >> bit) & 3;
if (entry) {
Mul(*this, *aMult[entry]);
ModNormalized(*this, cc);
anySet = true;
}
}
// Denormalize the result
Shr(*this, shift);
}
//===========================================================================
void BigNum::Rand (const BigNum & a, BigNum * seed) {
// this = random number less than a
ASSERT(seed != &a);
ASSERT(seed != this);
// Verify that a is distinct from this
BigNum distinctTemp;
const BigNum & aa = (&a != this) ? a : distinctTemp;
if (&aa != &a) {
ALLOC_TEMP(distinctTemp, a.Count());
distinctTemp.Set(a);
}
// Count the number of bits in a
unsigned bits = aa.HighBitPos() + 1;
for (;;) {
// Generate a random number with the same number of bits as a
Rand(bits, seed);
// Check whether the number is less than a
if (Compare(aa) < 0)
break;
}
}
//===========================================================================
void BigNum::Rand (unsigned bits, BigNum * seed) {
// this = random number with bits or fewer bits
ASSERT(seed != this);
// Prepare the output buffer
const unsigned count = (bits + 8 * sizeof(Val) - 1) / (8 * sizeof(Val));
SetCount(count);
if (!count)
return;
// Prepare the seed
unsigned seedCount = seed->Count();
if (!seedCount)
seed->SetCount(++seedCount);
unsigned seedIndex = 0;
// Produce a random number with the correct number of words
for (unsigned index = 0; index < count; ++index) {
// Read the next word of the seed
dword randValue = (*seed)[seedIndex] ^ ((index == seedIndex) ? 0x075bd924 : 0);
// Produce one word of randomness, 16 bits at a time
Val value = 0;
for (unsigned bit = 0; bit < 8 * sizeof(Val); bit += 16) {
const dword A = 0xbc8f;
const dword Q = 0xadc8;
const dword R = 0x0d47;
dword div = randValue / Q;
randValue = A * (randValue - Q * div) - R * div;
randValue &= 0x7fffffff;
value |= (randValue & 0xffff) << bit;
}
// Store the random word
SetVal(index, value);
// Update the seed and move to the seed next word
seed->SetVal(seedIndex, (Val)randValue);
if (++seedIndex >= seedCount)
seedIndex = 0;
}
// Mask the final word to contain the correct number of bits
Val mask = (Val)((Val)-1 >> (count * 8 * sizeof(Val) - bits));
SetVal(count - 1, (Val)((*this)[count - 1] & mask));
// Trim the result
Trim(count);
// Rotate the seed so the next unused seed word will be the first seed
// word used in the next random operation
if (seedIndex) {
BigNum saved;
ALLOC_TEMP(saved, seedCount);
saved.Set(*seed);
for (unsigned index = 0; index < seedCount; ++index)
(*seed)[index] = saved[(index + seedIndex) % seedCount];
}
}
//===========================================================================
void BigNum::RandPrime (unsigned bits, BigNum * seed) {
// Calculate the required number of words to hold the generated number
unsigned count = (bits + 8 * sizeof(Val) - 1) / (8 * sizeof(Val));
// For large bit counts, calculate the prime number as 2 * q * n + 1,
// where q is a random prime with fewer bits, and n is a random number
// chosen as follows:
// n >= (2 ^ (bits - 1) - 1) / (2 * q)
// n < (2 ^ bits - 1) / (2 * q)
if (bits > 128) {
// Choose a prime number q, and multiply it by 2
BigNum q_2;
ALLOC_TEMP(q_2, count / 2 + 2);
q_2.RandPrime(bits / 2, seed);
q_2.Mul(q_2, 2);
// Calculate the lower bound
BigNum lowerBound;
ALLOC_TEMP(lowerBound, count + 1);
lowerBound.SetBits(0, bits - 1);
lowerBound.Div(lowerBound, q_2, nil);
// Calculate the upper bound
BigNum upperBound;
ALLOC_TEMP(upperBound, count + 1);
upperBound.SetBits(0, bits);
upperBound.Div(upperBound, q_2, nil);
// Calculate the number of bits in the upper bound
unsigned upperBoundBits = upperBound.HighBitPos() + 1;
for (;;) {
// Choose a random number between the lower and upper bounds
Rand(upperBoundBits, seed);
if (Compare(upperBound) >= 0)
continue;
if (Compare(lowerBound) < 0)
continue;
// Calculate 2 * q * n + 1
Mul(*this, q_2);
Add(*this, 1);
// Test whether the result is prime
if (IsPrime())
break;
}
}
// For small bit counts, choose a random number with the requested
// number of bits, then keep incrementing it until we find a prime
else {
// Define the upper bound for a number with the requested number
// of bits
BigNum bound;
ALLOC_TEMP(bound, count + 1);
bound.SetBits(bits, 1);
for (;;) {
// Choose a random number with (bits - 1) bits
Rand(bits - 1, seed);
// Subtract it from the upper bound to generate a number with
// the high bit set
Sub(bound, *this);
// Keep incrementing the number until we find a prime
if (!IsOdd())
Add(*this, 1);
while (!IsPrime())
Add(*this, 2);
// If the number reached or exceeded the upper bound, try again
if (Compare(bound) < 0)
break;
}
}
}
//===========================================================================
void BigNum::Set (const BigNum & a) {
// this = a
if (&a == this)
return;
const unsigned count = a.Count();
SetCount(count);
for (unsigned index = count; index--; )
SetVal(index, a[index]);
}
//===========================================================================
void BigNum::Set (unsigned a) {
// this = a
ZeroCount();
if (a)
for (unsigned index = 0; ; ++index) {
SetCount(index + 1);
SetVal(index, LOW(a));
if (a < VAL_RANGE)
break;
a = (unsigned)(a / VAL_RANGE);
}
}
//===========================================================================
void BigNum::SetBits (unsigned setBitsOffset, unsigned setBitsCount) {
// this = binary [1...][0...], where 'setBitsOffset' is the number of
// zero bits and 'setBitsCount' is the number of one bits
if (!setBitsCount) {
ZeroCount();
return;
}
const unsigned setBitsTerm = setBitsOffset + setBitsCount - 1;
const unsigned bitsPerWord = 8 * sizeof(Val);
const unsigned firstSetWord = setBitsOffset / bitsPerWord;
const unsigned lastSetWord = (setBitsOffset + setBitsCount - 1) / bitsPerWord;
Val firstSetMask = (Val)((Val)-1 << (setBitsOffset % bitsPerWord));
Val lastSetMask = (Val)((Val)-1 >> (bitsPerWord - setBitsTerm % bitsPerWord - 1));
if (firstSetWord == lastSetWord)
firstSetMask = lastSetMask = (Val)(firstSetMask & lastSetMask);
SetCount(lastSetWord + 1);
unsigned index = 0;
for (; index < firstSetWord; ++index)
SetVal(index, 0);
SetVal(index++, firstSetMask);
if (firstSetWord == lastSetWord)
return;
for (; index < lastSetWord; ++index)
SetVal(index, (Val)-1);
SetVal(index, lastSetMask);
}
//===========================================================================
void BigNum::SetOne () {
// this = 1
SetCount(1);
SetVal(0, 1);
}
//===========================================================================
void BigNum::SetZero () {
// this = 0
ZeroCount();
}
//===========================================================================
void BigNum::Shl (const BigNum & a, unsigned b) {
// this = a << b
ASSERT(b < 8 * sizeof(Val));
if (!b) {
Set(a);
return;
}
const unsigned bInv = 8 * sizeof(Val) - b;
const unsigned count = a.Count();
SetCount(count + 1);
Val curr = 0;
for (unsigned index = count; index >= 1; --index) {
Val next = a[index - 1];
SetVal(index, (Val)((next >> bInv) | (curr << b)));
curr = next;
}
SetVal(0, (Val)(curr << b));
Trim(count + 1);
}
//===========================================================================
void BigNum::Shr (const BigNum & a, unsigned b) {
// this = a >> b
ASSERT(b < 8 * sizeof(Val));
if (!b) {
Set(a);
return;
}
const unsigned bInv = 8 * sizeof(Val) - b;
const unsigned count = a.Count();
SetCount(count);
if (!count)
return;
Val curr = a[0];
for (unsigned index = 0; index + 1 < count; ++index) {
Val next = a[index + 1];
SetVal(index, (Val)((next << bInv) | (curr >> b)));
curr = next;
}
SetVal(count - 1, (Val)(curr >> b));
Trim(count);
}
//===========================================================================
void BigNum::Square (const BigNum & a) {
// this = a * a
const unsigned aCount = a.Count();
const unsigned count = 2 * aCount;
SetCount(count);
if (!count)
return;
// We perform the multiplication from left to right, so that we don't
// overwrite any operand words before they're used in the case that
// the destination is not distinct from the operand
SetVal(count - 1, 0);
for (unsigned index = count - 1; index--; ) {
// Iterate every combination of source indices that adds up to
// index, and sum the products of those words
DVal value = 0;
unsigned aIndex = (index < aCount) ? 0 : (index + 1 - aCount);
unsigned bIndex;
for (; (int)((bIndex = index - aIndex) - aIndex) >= 0; ++aIndex) {
// Calculate the product of this pair of words
DVal product = Mul(a[aIndex], a[bIndex]);
// Add the product to the sum. If it exceeds the word size,
// apply carry.
value = (DVal)(value + product);
Val carry = HIGH(value);
unsigned carryIndex;
for (carryIndex = index + 1; carry; ++carryIndex)
SetVal(carryIndex, (DVal)((DVal)(*this)[carryIndex] + (DVal)carry), &carry);
value = LOW(value);
// If this pair of words should be multiplied twice, add the
// product again.
if (aIndex == bIndex)
continue;
value = (DVal)(value + product);
carry = HIGH(value);
for (carryIndex = index + 1; carry; ++carryIndex)
SetVal(carryIndex, (DVal)((DVal)(*this)[carryIndex] + (DVal)carry), &carry);
value = LOW(value);
}
// Store the sum of products as the final value for index
SetVal(index, LOW(value));
}
Trim(count);
}
//===========================================================================
void BigNum::Sub (const BigNum & a, Val b) {
// this = a - b
const unsigned count = a.Count();
SetCount(count);
Val borrow = b;
unsigned index;
for (index = 0; index < count; ++index) {
SetVal(index, (DVal)((DVal)a[index] - (DVal)borrow), &borrow);
borrow = (Val)((Val)0 - (Val)borrow);
}
ASSERT(!borrow);
Trim(index);
}
//===========================================================================
void BigNum::Sub (const BigNum & a, const BigNum & b) {
// this = a - b
const unsigned count = a.Count();
const unsigned bCount = b.Count();
GrowToCount(count, true);
Val borrow = 0;
unsigned index;
for (index = 0; index < count; ++index) {
Val bVal = (index < bCount) ? b[index] : (Val)0;
SetVal(index, (DVal)((DVal)a[index] - (DVal)bVal - (DVal)borrow), &borrow);
borrow = (Val)((Val)0 - (Val)borrow);
}
ASSERT(!borrow);
Trim(index);
}
//===========================================================================
void BigNum::ToStr (BigNum * buffer, Val radix) const {
ASSERT(this != buffer);
// Calculate the number of characters in the prefix
unsigned prefixChars;
if (radix == 16)
prefixChars = 2;
else if (radix == 8)
prefixChars = 1;
else
prefixChars = 0;
// Preallocate space for the output string
unsigned charsPerVal = 0;
for (Val testVal = (Val)-1; testVal; testVal = (Val)(testVal / radix))
++charsPerVal;
const unsigned charsTotal = max(1, Count()) * charsPerVal + prefixChars + 1;
buffer->SetCount((charsTotal * sizeof(wchar) + sizeof(Val) - 1) / sizeof(Val));
// Build the prefix
wchar * prefix = (wchar *)buffer->Ptr();
if (prefixChars) {
prefix[0] = L'0';
if (radix == 16)
prefix[1] = L'x';
else
ASSERT(prefixChars == 1);
}
// Build the number starting with the least significant digit
wchar * start = prefix + prefixChars;
wchar * curr = start;
BigNum work;
ALLOC_TEMP(work, Count());
work.Set(*this);
do {
// Extract the next value
Val remainder;
work.Div(work, radix, &remainder);
// Encode it as a character in the output string
if (remainder >= 10)
*curr++ = (wchar)(L'a' + (unsigned)remainder - 10);
else
*curr++ = (wchar)(L'0' + (unsigned)remainder);
} while (work.Count());
*curr = 0;
// Reverse the order of the output string
for (wchar * left = start, * right = curr - 1; left < right; ++left, --right)
SWAP(*left, *right);
}