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Minor optimizations in BigInteger

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This commit is contained in:
Milo Yip 2014-09-16 19:23:28 +08:00
parent 299e9f1e32
commit 5171775d4c
1 changed files with 33 additions and 26 deletions
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59
include/rapidjson/internal/biginteger.h
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@ -30,6 +30,10 @@ class BigInteger {
public:
typedef uint64_t Type;
BigInteger(const BigInteger& rhs) : count_(rhs.count_) {
std::memcpy(digits_, rhs.digits_, count_ * sizeof(Type));
}
explicit BigInteger(uint64_t u) : count_(1) {
digits_[0] = u;
}
@ -75,6 +79,8 @@ public:
BigInteger& operator*=(uint64_t u) {
if (u == 0) return *this = 0;
if (u == 1) return *this;
if (*this == 1) return *this = u;
uint64_t k = 0;
for (size_t i = 0; i < count_; i++) {
uint64_t hi;
@ -91,6 +97,8 @@ public:
BigInteger& operator*=(uint32_t u) {
if (u == 0) return *this = 0;
if (u == 1) return *this;
if (*this == 1) return *this = u;
uint32_t k = 0;
for (size_t i = 0; i < count_; i++) {
const uint64_t c = digits_[i] >> 32;
@ -110,32 +118,27 @@ public:
}
BigInteger& operator<<=(size_t shift) {
if (IsZero()) return *this;
if (IsZero() || shift == 0) return *this;
if (shift >= kTypeBit) {
size_t offset = shift / kTypeBit;
RAPIDJSON_ASSERT(count_ + offset <= kCapacity);
for (size_t i = count_; i > 0; i--)
digits_[i - 1 + offset] = digits_[i - 1];
for (size_t i = 0; i < offset; i++)
digits_[i] = 0;
size_t offset = shift / kTypeBit;
size_t interShift = shift % kTypeBit;
RAPIDJSON_ASSERT(count_ + offset <= kCapacity);
if (interShift == 0) {
std::memmove(&digits_[count_ - 1 + offset], &digits_[count_ - 1], count_ * sizeof(Type));
count_ += offset;
shift -= offset * kTypeBit;
}
else {
digits_[count_] = 0;
for (size_t i = count_; i > 0; i--)
digits_[i + offset] = (digits_[i] << interShift) | (digits_[i - 1] >> (kTypeBit - interShift));
digits_[offset] = digits_[0] << interShift;
count_ += offset;
if (digits_[count_])
count_++;
}
if (shift > 0) {
// Inter-digit shifts
Type carry = 0;
for (size_t i = 0; i < count_; i++) {
Type newCarry = digits_[i] >> (kTypeBit - shift);
digits_[i] = (digits_[i] << shift) | carry;
carry = newCarry;
}
// Last carry
if (carry)
PushBack(carry);
}
std::memset(digits_, 0, offset * sizeof(Type));
return *this;
}
@ -144,6 +147,10 @@ public:
return count_ == rhs.count_ && memcmp(digits_, rhs.digits_, count_ * sizeof(Type)) == 0;
}
bool operator==(const Type rhs) const {
return count_ == 1 && digits_[0] == rhs;
}
BigInteger& MultiplyPow5(unsigned exp) {
static const uint32_t kPow5[12] = {
5,
@ -160,10 +167,9 @@ public:
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
};
if (exp == 0) return *this;
unsigned e = exp;
for (; e >= 27; e -= 27) *this *= RAPIDJSON_UINT64_C2(0X6765C793, 0XFA10079D); // 5^27
for (; e >= 13; e -= 13) *this *= 1220703125u; // 5^13
if (e > 0) *this *= kPow5[e - 1];
for (; exp >= 27; exp -= 27) *this *= RAPIDJSON_UINT64_C2(0X6765C793, 0XFA10079D); // 5^27
for (; exp >= 13; exp -= 13) *this *= 1220703125u; // 5^13
if (exp > 0) *this *= kPow5[exp - 1];
return *this;
}
@ -277,6 +283,7 @@ private:
Type digits_[kCapacity];
size_t count_;
};
} // namespace internal
} // namespace rapidjson