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35 namespace double_conversion {
38 : bigits_(bigits_buffer_, kBigitCapacity), used_digits_(0), exponent_(0) {
39 for (int i = 0; i < kBigitCapacity; ++i) {
46 static int BitSize(S value) {
47 return 8 * sizeof(value);
50 // Guaranteed to lie in one Bigit.
51 void Bignum::AssignUInt16(uint16_t value) {
52 ASSERT(kBigitSize >= BitSize(value));
54 if (value == 0) return;
62 void Bignum::AssignUInt64(uint64_t value) {
63 const int kUInt64Size = 64;
66 if (value == 0) return;
68 int needed_bigits = kUInt64Size / kBigitSize + 1;
69 EnsureCapacity(needed_bigits);
70 for (int i = 0; i < needed_bigits; ++i) {
71 bigits_[i] = (uint32_t)value & kBigitMask;
72 value = value >> kBigitSize;
74 used_digits_ = needed_bigits;
79 void Bignum::AssignBignum(const Bignum& other) {
80 exponent_ = other.exponent_;
81 for (int i = 0; i < other.used_digits_; ++i) {
82 bigits_[i] = other.bigits_[i];
84 // Clear the excess digits (if there were any).
85 for (int i = other.used_digits_; i < used_digits_; ++i) {
88 used_digits_ = other.used_digits_;
92 static uint64_t ReadUInt64(Vector<const char> buffer,
96 for (int i = from; i < from + digits_to_read; ++i) {
97 int digit = buffer[i] - '0';
98 ASSERT(0 <= digit && digit <= 9);
99 result = result * 10 + digit;
105 void Bignum::AssignDecimalString(Vector<const char> value) {
106 // 2^64 = 18446744073709551616 > 10^19
107 const int kMaxUint64DecimalDigits = 19;
109 int length = value.length();
111 // Let's just say that each digit needs 4 bits.
112 while (length >= kMaxUint64DecimalDigits) {
113 uint64_t digits = ReadUInt64(value, pos, kMaxUint64DecimalDigits);
114 pos += kMaxUint64DecimalDigits;
115 length -= kMaxUint64DecimalDigits;
116 MultiplyByPowerOfTen(kMaxUint64DecimalDigits);
119 uint64_t digits = ReadUInt64(value, pos, length);
120 MultiplyByPowerOfTen(length);
126 static int HexCharValue(char c) {
127 if ('0' <= c && c <= '9') return c - '0';
128 if ('a' <= c && c <= 'f') return 10 + c - 'a';
129 if ('A' <= c && c <= 'F') return 10 + c - 'A';
131 return 0; // To make compiler happy.
135 void Bignum::AssignHexString(Vector<const char> value) {
137 int length = value.length();
139 int needed_bigits = length * 4 / kBigitSize + 1;
140 EnsureCapacity(needed_bigits);
141 int string_index = length - 1;
142 for (int i = 0; i < needed_bigits - 1; ++i) {
143 // These bigits are guaranteed to be "full".
144 Chunk current_bigit = 0;
145 for (int j = 0; j < kBigitSize / 4; j++) {
146 current_bigit += HexCharValue(value[string_index--]) << (j * 4);
148 bigits_[i] = current_bigit;
150 used_digits_ = needed_bigits - 1;
152 Chunk most_significant_bigit = 0; // Could be = 0;
153 for (int j = 0; j <= string_index; ++j) {
154 most_significant_bigit <<= 4;
155 most_significant_bigit += HexCharValue(value[j]);
157 if (most_significant_bigit != 0) {
158 bigits_[used_digits_] = most_significant_bigit;
165 void Bignum::AddUInt64(uint64_t operand) {
166 if (operand == 0) return;
168 other.AssignUInt64(operand);
173 void Bignum::AddBignum(const Bignum& other) {
175 ASSERT(other.IsClamped());
177 // If this has a greater exponent than other append zero-bigits to this.
178 // After this call exponent_ <= other.exponent_.
181 // There are two possibilities:
182 // aaaaaaaaaaa 0000 (where the 0s represent a's exponent)
191 // In both cases we might need a carry bigit.
193 EnsureCapacity(1 + Max(BigitLength(), other.BigitLength()) - exponent_);
195 int bigit_pos = other.exponent_ - exponent_;
196 ASSERT(bigit_pos >= 0);
197 for (int i = 0; i < other.used_digits_; ++i) {
198 Chunk sum = bigits_[bigit_pos] + other.bigits_[i] + carry;
199 bigits_[bigit_pos] = sum & kBigitMask;
200 carry = sum >> kBigitSize;
205 Chunk sum = bigits_[bigit_pos] + carry;
206 bigits_[bigit_pos] = sum & kBigitMask;
207 carry = sum >> kBigitSize;
210 used_digits_ = Max(bigit_pos, used_digits_);
215 void Bignum::SubtractBignum(const Bignum& other) {
217 ASSERT(other.IsClamped());
218 // We require this to be bigger than other.
219 ASSERT(LessEqual(other, *this));
223 int offset = other.exponent_ - exponent_;
226 for (i = 0; i < other.used_digits_; ++i) {
227 ASSERT((borrow == 0) || (borrow == 1));
228 Chunk difference = bigits_[i + offset] - other.bigits_[i] - borrow;
229 bigits_[i + offset] = difference & kBigitMask;
230 borrow = difference >> (kChunkSize - 1);
232 while (borrow != 0) {
233 Chunk difference = bigits_[i + offset] - borrow;
234 bigits_[i + offset] = difference & kBigitMask;
235 borrow = difference >> (kChunkSize - 1);
242 void Bignum::ShiftLeft(int shift_amount) {
243 if (used_digits_ == 0) return;
244 exponent_ += shift_amount / kBigitSize;
245 int local_shift = shift_amount % kBigitSize;
246 EnsureCapacity(used_digits_ + 1);
247 BigitsShiftLeft(local_shift);
251 void Bignum::MultiplyByUInt32(uint32_t factor) {
252 if (factor == 1) return;
257 if (used_digits_ == 0) return;
259 // The product of a bigit with the factor is of size kBigitSize + 32.
260 // Assert that this number + 1 (for the carry) fits into double chunk.
261 ASSERT(kDoubleChunkSize >= kBigitSize + 32 + 1);
262 DoubleChunk carry = 0;
263 for (int i = 0; i < used_digits_; ++i) {
264 DoubleChunk product = static_cast<DoubleChunk>(factor) * bigits_[i] + carry;
265 bigits_[i] = static_cast<Chunk>(product & kBigitMask);
266 carry = (product >> kBigitSize);
269 EnsureCapacity(used_digits_ + 1);
270 bigits_[used_digits_] = (uint32_t)carry & kBigitMask;
272 carry >>= kBigitSize;
277 void Bignum::MultiplyByUInt64(uint64_t factor) {
278 if (factor == 1) return;
283 ASSERT(kBigitSize < 32);
285 uint64_t low = factor & 0xFFFFFFFF;
286 uint64_t high = factor >> 32;
287 for (int i = 0; i < used_digits_; ++i) {
288 uint64_t product_low = low * bigits_[i];
289 uint64_t product_high = high * bigits_[i];
290 uint64_t tmp = (carry & kBigitMask) + product_low;
291 bigits_[i] = (uint32_t)tmp & kBigitMask;
292 carry = (carry >> kBigitSize) + (tmp >> kBigitSize) +
293 (product_high << (32 - kBigitSize));
296 EnsureCapacity(used_digits_ + 1);
297 bigits_[used_digits_] = (uint32_t)carry & kBigitMask;
299 carry >>= kBigitSize;
304 void Bignum::MultiplyByPowerOfTen(int exponent) {
305 const uint64_t kFive27 = UINT64_2PART_C(0x6765c793, fa10079d);
306 const uint16_t kFive1 = 5;
307 const uint16_t kFive2 = kFive1 * 5;
308 const uint16_t kFive3 = kFive2 * 5;
309 const uint16_t kFive4 = kFive3 * 5;
310 const uint16_t kFive5 = kFive4 * 5;
311 const uint16_t kFive6 = kFive5 * 5;
312 const uint32_t kFive7 = kFive6 * 5;
313 const uint32_t kFive8 = kFive7 * 5;
314 const uint32_t kFive9 = kFive8 * 5;
315 const uint32_t kFive10 = kFive9 * 5;
316 const uint32_t kFive11 = kFive10 * 5;
317 const uint32_t kFive12 = kFive11 * 5;
318 const uint32_t kFive13 = kFive12 * 5;
319 const uint32_t kFive1_to_12[] =
320 { kFive1, kFive2, kFive3, kFive4, kFive5, kFive6,
321 kFive7, kFive8, kFive9, kFive10, kFive11, kFive12 };
323 ASSERT(exponent >= 0);
324 if (exponent == 0) return;
325 if (used_digits_ == 0) return;
327 // We shift by exponent at the end just before returning.
328 int remaining_exponent = exponent;
329 while (remaining_exponent >= 27) {
330 MultiplyByUInt64(kFive27);
331 remaining_exponent -= 27;
333 while (remaining_exponent >= 13) {
334 MultiplyByUInt32(kFive13);
335 remaining_exponent -= 13;
337 if (remaining_exponent > 0) {
338 MultiplyByUInt32(kFive1_to_12[remaining_exponent - 1]);
344 void Bignum::Square() {
346 int product_length = 2 * used_digits_;
347 EnsureCapacity(product_length);
349 // Comba multiplication: compute each column separately.
350 // Example: r = a2a1a0 * b2b1b0.
352 // 10 * (a1b0 + a0b1) +
353 // 100 * (a2b0 + a1b1 + a0b2) +
354 // 1000 * (a2b1 + a1b2) +
357 // In the worst case we have to accumulate nb-digits products of digit*digit.
359 // Assert that the additional number of bits in a DoubleChunk are enough to
360 // sum up used_digits of Bigit*Bigit.
361 if ((1 << (2 * (kChunkSize - kBigitSize))) <= used_digits_) {
364 DoubleChunk accumulator = 0;
365 // First shift the digits so we don't overwrite them.
366 int copy_offset = used_digits_;
367 for (int i = 0; i < used_digits_; ++i) {
368 bigits_[copy_offset + i] = bigits_[i];
370 // We have two loops to avoid some 'if's in the loop.
371 for (int i = 0; i < used_digits_; ++i) {
372 // Process temporary digit i with power i.
373 // The sum of the two indices must be equal to i.
374 int bigit_index1 = i;
375 int bigit_index2 = 0;
376 // Sum all of the sub-products.
377 while (bigit_index1 >= 0) {
378 Chunk chunk1 = bigits_[copy_offset + bigit_index1];
379 Chunk chunk2 = bigits_[copy_offset + bigit_index2];
380 accumulator += static_cast<DoubleChunk>(chunk1) * chunk2;
384 bigits_[i] = static_cast<Chunk>(accumulator) & kBigitMask;
385 accumulator >>= kBigitSize;
387 for (int i = used_digits_; i < product_length; ++i) {
388 int bigit_index1 = used_digits_ - 1;
389 int bigit_index2 = i - bigit_index1;
390 // Invariant: sum of both indices is again equal to i.
391 // Inner loop runs 0 times on last iteration, emptying accumulator.
392 while (bigit_index2 < used_digits_) {
393 Chunk chunk1 = bigits_[copy_offset + bigit_index1];
394 Chunk chunk2 = bigits_[copy_offset + bigit_index2];
395 accumulator += static_cast<DoubleChunk>(chunk1) * chunk2;
399 // The overwritten bigits_[i] will never be read in further loop iterations,
400 // because bigit_index1 and bigit_index2 are always greater
401 // than i - used_digits_.
402 bigits_[i] = static_cast<Chunk>(accumulator) & kBigitMask;
403 accumulator >>= kBigitSize;
405 // Since the result was guaranteed to lie inside the number the
406 // accumulator must be 0 now.
407 ASSERT(accumulator == 0);
409 // Don't forget to update the used_digits and the exponent.
410 used_digits_ = product_length;
416 void Bignum::AssignPowerUInt16(uint16_t base, int power_exponent) {
418 ASSERT(power_exponent >= 0);
419 if (power_exponent == 0) {
425 // We expect base to be in range 2-32, and most often to be 10.
426 // It does not make much sense to implement different algorithms for counting
428 while ((base & 1) == 0) {
434 while (tmp_base != 0) {
438 int final_size = bit_size * power_exponent;
439 // 1 extra bigit for the shifting, and one for rounded final_size.
440 EnsureCapacity(final_size / kBigitSize + 2);
442 // Left to Right exponentiation.
444 while (power_exponent >= mask) mask <<= 1;
446 // The mask is now pointing to the bit above the most significant 1-bit of
448 // Get rid of first 1-bit;
450 uint64_t this_value = base;
452 bool delayed_multipliciation = false;
453 const uint64_t max_32bits = 0xFFFFFFFF;
454 while (mask != 0 && this_value <= max_32bits) {
455 this_value = this_value * this_value;
456 // Verify that there is enough space in this_value to perform the
457 // multiplication. The first bit_size bits must be 0.
458 if ((power_exponent & mask) != 0) {
459 uint64_t base_bits_mask =
460 ~((static_cast<uint64_t>(1) << (64 - bit_size)) - 1);
461 bool high_bits_zero = (this_value & base_bits_mask) == 0;
462 if (high_bits_zero) {
465 delayed_multipliciation = true;
470 AssignUInt64(this_value);
471 if (delayed_multipliciation) {
472 MultiplyByUInt32(base);
475 // Now do the same thing as a bignum.
478 if ((power_exponent & mask) != 0) {
479 MultiplyByUInt32(base);
484 // And finally add the saved shifts.
485 ShiftLeft(shifts * power_exponent);
489 // Precondition: this/other < 16bit.
490 uint16_t Bignum::DivideModuloIntBignum(const Bignum& other) {
492 ASSERT(other.IsClamped());
493 ASSERT(other.used_digits_ > 0);
495 // Easy case: if we have less digits than the divisor than the result is 0.
496 // Note: this handles the case where this == 0, too.
497 if (BigitLength() < other.BigitLength()) {
505 // Start by removing multiples of 'other' until both numbers have the same
507 while (BigitLength() > other.BigitLength()) {
508 // This naive approach is extremely inefficient if the this divided other
509 // might be big. This function is implemented for doubleToString where
510 // the result should be small (less than 10).
511 ASSERT(other.bigits_[other.used_digits_ - 1] >= ((1 << kBigitSize) / 16));
512 // Remove the multiples of the first digit.
513 // Example this = 23 and other equals 9. -> Remove 2 multiples.
514 result += bigits_[used_digits_ - 1];
515 SubtractTimes(other, bigits_[used_digits_ - 1]);
518 ASSERT(BigitLength() == other.BigitLength());
520 // Both bignums are at the same length now.
521 // Since other has more than 0 digits we know that the access to
522 // bigits_[used_digits_ - 1] is safe.
523 Chunk this_bigit = bigits_[used_digits_ - 1];
524 Chunk other_bigit = other.bigits_[other.used_digits_ - 1];
526 if (other.used_digits_ == 1) {
527 // Shortcut for easy (and common) case.
528 int quotient = this_bigit / other_bigit;
529 bigits_[used_digits_ - 1] = this_bigit - other_bigit * quotient;
535 int division_estimate = this_bigit / (other_bigit + 1);
536 result += division_estimate;
537 SubtractTimes(other, division_estimate);
539 if (other_bigit * (division_estimate + 1) > this_bigit) {
540 // No need to even try to subtract. Even if other's remaining digits were 0
541 // another subtraction would be too much.
545 while (LessEqual(other, *this)) {
546 SubtractBignum(other);
554 static int SizeInHexChars(S number) {
557 while (number != 0) {
565 static char HexCharOfValue(int value) {
566 ASSERT(0 <= value && value <= 16);
567 if (value < 10) return value + '0';
568 return value - 10 + 'A';
572 bool Bignum::ToHexString(char* buffer, int buffer_size) const {
574 // Each bigit must be printable as separate hex-character.
575 ASSERT(kBigitSize % 4 == 0);
576 const int kHexCharsPerBigit = kBigitSize / 4;
578 if (used_digits_ == 0) {
579 if (buffer_size < 2) return false;
584 // We add 1 for the terminating '\0' character.
585 int needed_chars = (BigitLength() - 1) * kHexCharsPerBigit +
586 SizeInHexChars(bigits_[used_digits_ - 1]) + 1;
587 if (needed_chars > buffer_size) return false;
588 int string_index = needed_chars - 1;
589 buffer[string_index--] = '\0';
590 for (int i = 0; i < exponent_; ++i) {
591 for (int j = 0; j < kHexCharsPerBigit; ++j) {
592 buffer[string_index--] = '0';
595 for (int i = 0; i < used_digits_ - 1; ++i) {
596 Chunk current_bigit = bigits_[i];
597 for (int j = 0; j < kHexCharsPerBigit; ++j) {
598 buffer[string_index--] = HexCharOfValue(current_bigit & 0xF);
602 // And finally the last bigit.
603 Chunk most_significant_bigit = bigits_[used_digits_ - 1];
604 while (most_significant_bigit != 0) {
605 buffer[string_index--] = HexCharOfValue(most_significant_bigit & 0xF);
606 most_significant_bigit >>= 4;
612 Bignum::Chunk Bignum::BigitAt(int index) const {
613 if (index >= BigitLength()) return 0;
614 if (index < exponent_) return 0;
615 return bigits_[index - exponent_];
619 int Bignum::Compare(const Bignum& a, const Bignum& b) {
620 ASSERT(a.IsClamped());
621 ASSERT(b.IsClamped());
622 int bigit_length_a = a.BigitLength();
623 int bigit_length_b = b.BigitLength();
624 if (bigit_length_a < bigit_length_b) return -1;
625 if (bigit_length_a > bigit_length_b) return +1;
626 for (int i = bigit_length_a - 1; i >= Min(a.exponent_, b.exponent_); --i) {
627 Chunk bigit_a = a.BigitAt(i);
628 Chunk bigit_b = b.BigitAt(i);
629 if (bigit_a < bigit_b) return -1;
630 if (bigit_a > bigit_b) return +1;
631 // Otherwise they are equal up to this digit. Try the next digit.
637 int Bignum::PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c) {
638 ASSERT(a.IsClamped());
639 ASSERT(b.IsClamped());
640 ASSERT(c.IsClamped());
641 if (a.BigitLength() < b.BigitLength()) {
642 return PlusCompare(b, a, c);
644 if (a.BigitLength() + 1 < c.BigitLength()) return -1;
645 if (a.BigitLength() > c.BigitLength()) return +1;
646 // The exponent encodes 0-bigits. So if there are more 0-digits in 'a' than
647 // 'b' has digits, then the bigit-length of 'a'+'b' must be equal to the one
649 if (a.exponent_ >= b.BigitLength() && a.BigitLength() < c.BigitLength()) {
654 // Starting at min_exponent all digits are == 0. So no need to compare them.
655 int min_exponent = Min(Min(a.exponent_, b.exponent_), c.exponent_);
656 for (int i = c.BigitLength() - 1; i >= min_exponent; --i) {
657 Chunk chunk_a = a.BigitAt(i);
658 Chunk chunk_b = b.BigitAt(i);
659 Chunk chunk_c = c.BigitAt(i);
660 Chunk sum = chunk_a + chunk_b;
661 if (sum > chunk_c + borrow) {
664 borrow = chunk_c + borrow - sum;
665 if (borrow > 1) return -1;
666 borrow <<= kBigitSize;
669 if (borrow == 0) return 0;
674 void Bignum::Clamp() {
675 while (used_digits_ > 0 && bigits_[used_digits_ - 1] == 0) {
678 if (used_digits_ == 0) {
685 bool Bignum::IsClamped() const {
686 return used_digits_ == 0 || bigits_[used_digits_ - 1] != 0;
690 void Bignum::Zero() {
691 for (int i = 0; i < used_digits_; ++i) {
699 void Bignum::Align(const Bignum& other) {
700 if (exponent_ > other.exponent_) {
701 // If "X" represents a "hidden" digit (by the exponent) then we are in the
702 // following case (a == this, b == other):
703 // a: aaaaaaXXXX or a: aaaaaXXX
704 // b: bbbbbbX b: bbbbbbbbXX
705 // We replace some of the hidden digits (X) of a with 0 digits.
706 // a: aaaaaa000X or a: aaaaa0XX
707 int zero_digits = exponent_ - other.exponent_;
708 EnsureCapacity(used_digits_ + zero_digits);
709 for (int i = used_digits_ - 1; i >= 0; --i) {
710 bigits_[i + zero_digits] = bigits_[i];
712 for (int i = 0; i < zero_digits; ++i) {
715 used_digits_ += zero_digits;
716 exponent_ -= zero_digits;
717 ASSERT(used_digits_ >= 0);
718 ASSERT(exponent_ >= 0);
723 void Bignum::BigitsShiftLeft(int shift_amount) {
724 ASSERT(shift_amount < kBigitSize);
725 ASSERT(shift_amount >= 0);
727 for (int i = 0; i < used_digits_; ++i) {
728 Chunk new_carry = bigits_[i] >> (kBigitSize - shift_amount);
729 bigits_[i] = ((bigits_[i] << shift_amount) + carry) & kBigitMask;
733 bigits_[used_digits_] = carry;
739 void Bignum::SubtractTimes(const Bignum& other, int factor) {
740 ASSERT(exponent_ <= other.exponent_);
742 for (int i = 0; i < factor; ++i) {
743 SubtractBignum(other);
748 int exponent_diff = other.exponent_ - exponent_;
749 for (int i = 0; i < other.used_digits_; ++i) {
750 DoubleChunk product = static_cast<DoubleChunk>(factor) * other.bigits_[i];
751 DoubleChunk remove = borrow + product;
752 Chunk difference = bigits_[i + exponent_diff] - ((uint32_t)remove & kBigitMask);
753 bigits_[i + exponent_diff] = difference & kBigitMask;
754 borrow = static_cast<Chunk>((difference >> (kChunkSize - 1)) +
755 (remove >> kBigitSize));
757 for (int i = other.used_digits_ + exponent_diff; i < used_digits_; ++i) {
758 if (borrow == 0) return;
759 Chunk difference = bigits_[i] - borrow;
760 bigits_[i] = difference & kBigitMask;
761 borrow = difference >> (kChunkSize - 1);
768 } // namespace double_conversion