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27
28#include "config.h"
29
30#include <wtf/dtoa/bignum.h>
31
32#include <wtf/dtoa/utils.h>
33#include <wtf/ASCIICType.h>
34
35namespace WTF {
36namespace double_conversion {
37
38Bignum::Bignum()
39 : bigits_buffer_(), bigits_(bigits_buffer_, kBigitCapacity), used_digits_(0), exponent_(0) {
40 for (int i = 0; i < kBigitCapacity; ++i) {
41 bigits_[i] = 0;
42 }
43}
44
45
46template<typename S>
47static int BitSize(S value) {
48 (void) value; // Mark variable as used.
49 return 8 * sizeof(value);
50}
51
52// Guaranteed to lie in one Bigit.
53void Bignum::AssignUInt16(uint16_t value) {
54 ASSERT(kBigitSize >= BitSize(value));
55 Zero();
56 if (value == 0) return;
57
58 EnsureCapacity(1);
59 bigits_[0] = value;
60 used_digits_ = 1;
61}
62
63
64void Bignum::AssignUInt64(uint64_t value) {
65 const int kUInt64Size = 64;
66
67 Zero();
68 if (value == 0) return;
69
70 int needed_bigits = kUInt64Size / kBigitSize + 1;
71 EnsureCapacity(needed_bigits);
72 for (int i = 0; i < needed_bigits; ++i) {
73 bigits_[i] = value & kBigitMask;
74 value = value >> kBigitSize;
75 }
76 used_digits_ = needed_bigits;
77 Clamp();
78}
79
80
81void Bignum::AssignBignum(const Bignum& other) {
82 exponent_ = other.exponent_;
83 for (int i = 0; i < other.used_digits_; ++i) {
84 bigits_[i] = other.bigits_[i];
85 }
86 // Clear the excess digits (if there were any).
87 for (int i = other.used_digits_; i < used_digits_; ++i) {
88 bigits_[i] = 0;
89 }
90 used_digits_ = other.used_digits_;
91}
92
93
94static uint64_t ReadUInt64(BufferReference<const char> buffer,
95 int from,
96 int digits_to_read) {
97 uint64_t result = 0;
98 for (int i = from; i < from + digits_to_read; ++i) {
99 int digit = buffer[i] - '0';
100 ASSERT(0 <= digit && digit <= 9);
101 result = result * 10 + digit;
102 }
103 return result;
104}
105
106
107void Bignum::AssignDecimalString(BufferReference<const char> value) {
108 // 2^64 = 18446744073709551616 > 10^19
109 const int kMaxUint64DecimalDigits = 19;
110 Zero();
111 int length = value.length();
112 unsigned int pos = 0;
113 // Let's just say that each digit needs 4 bits.
114 while (length >= kMaxUint64DecimalDigits) {
115 uint64_t digits = ReadUInt64(value, pos, kMaxUint64DecimalDigits);
116 pos += kMaxUint64DecimalDigits;
117 length -= kMaxUint64DecimalDigits;
118 MultiplyByPowerOfTen(kMaxUint64DecimalDigits);
119 AddUInt64(digits);
120 }
121 uint64_t digits = ReadUInt64(value, pos, length);
122 MultiplyByPowerOfTen(length);
123 AddUInt64(digits);
124 Clamp();
125}
126
127
128void Bignum::AssignHexString(BufferReference<const char> value) {
129 Zero();
130 int length = value.length();
131
132 int needed_bigits = length * 4 / kBigitSize + 1;
133 EnsureCapacity(needed_bigits);
134 int string_index = length - 1;
135 for (int i = 0; i < needed_bigits - 1; ++i) {
136 // These bigits are guaranteed to be "full".
137 Chunk current_bigit = 0;
138 for (int j = 0; j < kBigitSize / 4; j++) {
139 current_bigit += toASCIIHexValue(value[string_index--]) << (j * 4);
140 }
141 bigits_[i] = current_bigit;
142 }
143 used_digits_ = needed_bigits - 1;
144
145 Chunk most_significant_bigit = 0; // Could be = 0;
146 for (int j = 0; j <= string_index; ++j) {
147 most_significant_bigit <<= 4;
148 most_significant_bigit += toASCIIHexValue(value[j]);
149 }
150 if (most_significant_bigit != 0) {
151 bigits_[used_digits_] = most_significant_bigit;
152 used_digits_++;
153 }
154 Clamp();
155}
156
157
158void Bignum::AddUInt64(uint64_t operand) {
159 if (operand == 0) return;
160 Bignum other;
161 other.AssignUInt64(operand);
162 AddBignum(other);
163}
164
165
166void Bignum::AddBignum(const Bignum& other) {
167 ASSERT(IsClamped());
168 ASSERT(other.IsClamped());
169
170 // If this has a greater exponent than other append zero-bigits to this.
171 // After this call exponent_ <= other.exponent_.
172 Align(other);
173
174 // There are two possibilities:
175 // aaaaaaaaaaa 0000 (where the 0s represent a's exponent)
176 // bbbbb 00000000
177 // ----------------
178 // ccccccccccc 0000
179 // or
180 // aaaaaaaaaa 0000
181 // bbbbbbbbb 0000000
182 // -----------------
183 // cccccccccccc 0000
184 // In both cases we might need a carry bigit.
185
186 EnsureCapacity(1 + Max(BigitLength(), other.BigitLength()) - exponent_);
187 Chunk carry = 0;
188 int bigit_pos = other.exponent_ - exponent_;
189 ASSERT(bigit_pos >= 0);
190 for (int i = 0; i < other.used_digits_; ++i) {
191 Chunk sum = bigits_[bigit_pos] + other.bigits_[i] + carry;
192 bigits_[bigit_pos] = sum & kBigitMask;
193 carry = sum >> kBigitSize;
194 bigit_pos++;
195 }
196
197 while (carry != 0) {
198 Chunk sum = bigits_[bigit_pos] + carry;
199 bigits_[bigit_pos] = sum & kBigitMask;
200 carry = sum >> kBigitSize;
201 bigit_pos++;
202 }
203 used_digits_ = Max(bigit_pos, used_digits_);
204 ASSERT(IsClamped());
205}
206
207
208void Bignum::SubtractBignum(const Bignum& other) {
209 ASSERT(IsClamped());
210 ASSERT(other.IsClamped());
211 // We require this to be bigger than other.
212 ASSERT(LessEqual(other, *this));
213
214 Align(other);
215
216 int offset = other.exponent_ - exponent_;
217 Chunk borrow = 0;
218 int i;
219 for (i = 0; i < other.used_digits_; ++i) {
220 ASSERT((borrow == 0) || (borrow == 1));
221 Chunk difference = bigits_[i + offset] - other.bigits_[i] - borrow;
222 bigits_[i + offset] = difference & kBigitMask;
223 borrow = difference >> (kChunkSize - 1);
224 }
225 while (borrow != 0) {
226 Chunk difference = bigits_[i + offset] - borrow;
227 bigits_[i + offset] = difference & kBigitMask;
228 borrow = difference >> (kChunkSize - 1);
229 ++i;
230 }
231 Clamp();
232}
233
234
235void Bignum::ShiftLeft(int shift_amount) {
236 if (used_digits_ == 0) return;
237 exponent_ += shift_amount / kBigitSize;
238 int local_shift = shift_amount % kBigitSize;
239 EnsureCapacity(used_digits_ + 1);
240 BigitsShiftLeft(local_shift);
241}
242
243
244void Bignum::MultiplyByUInt32(uint32_t factor) {
245 if (factor == 1) return;
246 if (factor == 0) {
247 Zero();
248 return;
249 }
250 if (used_digits_ == 0) return;
251
252 // The product of a bigit with the factor is of size kBigitSize + 32.
253 // Assert that this number + 1 (for the carry) fits into double chunk.
254 ASSERT(kDoubleChunkSize >= kBigitSize + 32 + 1);
255 DoubleChunk carry = 0;
256 for (int i = 0; i < used_digits_; ++i) {
257 DoubleChunk product = static_cast<DoubleChunk>(factor) * bigits_[i] + carry;
258 bigits_[i] = static_cast<Chunk>(product & kBigitMask);
259 carry = (product >> kBigitSize);
260 }
261 while (carry != 0) {
262 EnsureCapacity(used_digits_ + 1);
263 bigits_[used_digits_] = carry & kBigitMask;
264 used_digits_++;
265 carry >>= kBigitSize;
266 }
267}
268
269
270void Bignum::MultiplyByUInt64(uint64_t factor) {
271 if (factor == 1) return;
272 if (factor == 0) {
273 Zero();
274 return;
275 }
276 ASSERT(kBigitSize < 32);
277 uint64_t carry = 0;
278 uint64_t low = factor & 0xFFFFFFFF;
279 uint64_t high = factor >> 32;
280 for (int i = 0; i < used_digits_; ++i) {
281 uint64_t product_low = low * bigits_[i];
282 uint64_t product_high = high * bigits_[i];
283 uint64_t tmp = (carry & kBigitMask) + product_low;
284 bigits_[i] = tmp & kBigitMask;
285 carry = (carry >> kBigitSize) + (tmp >> kBigitSize) +
286 (product_high << (32 - kBigitSize));
287 }
288 while (carry != 0) {
289 EnsureCapacity(used_digits_ + 1);
290 bigits_[used_digits_] = carry & kBigitMask;
291 used_digits_++;
292 carry >>= kBigitSize;
293 }
294}
295
296
297void Bignum::MultiplyByPowerOfTen(int exponent) {
298 const uint64_t kFive27 = UINT64_2PART_C(0x6765c793, fa10079d);
299 const uint16_t kFive1 = 5;
300 const uint16_t kFive2 = kFive1 * 5;
301 const uint16_t kFive3 = kFive2 * 5;
302 const uint16_t kFive4 = kFive3 * 5;
303 const uint16_t kFive5 = kFive4 * 5;
304 const uint16_t kFive6 = kFive5 * 5;
305 const uint32_t kFive7 = kFive6 * 5;
306 const uint32_t kFive8 = kFive7 * 5;
307 const uint32_t kFive9 = kFive8 * 5;
308 const uint32_t kFive10 = kFive9 * 5;
309 const uint32_t kFive11 = kFive10 * 5;
310 const uint32_t kFive12 = kFive11 * 5;
311 const uint32_t kFive13 = kFive12 * 5;
312 const uint32_t kFive1_to_12[] =
313 { kFive1, kFive2, kFive3, kFive4, kFive5, kFive6,
314 kFive7, kFive8, kFive9, kFive10, kFive11, kFive12 };
315
316 ASSERT(exponent >= 0);
317 if (exponent == 0) return;
318 if (used_digits_ == 0) return;
319
320 // We shift by exponent at the end just before returning.
321 int remaining_exponent = exponent;
322 while (remaining_exponent >= 27) {
323 MultiplyByUInt64(kFive27);
324 remaining_exponent -= 27;
325 }
326 while (remaining_exponent >= 13) {
327 MultiplyByUInt32(kFive13);
328 remaining_exponent -= 13;
329 }
330 if (remaining_exponent > 0) {
331 MultiplyByUInt32(kFive1_to_12[remaining_exponent - 1]);
332 }
333 ShiftLeft(exponent);
334}
335
336
337void Bignum::Square() {
338 ASSERT(IsClamped());
339 int product_length = 2 * used_digits_;
340 EnsureCapacity(product_length);
341
342 // Comba multiplication: compute each column separately.
343 // Example: r = a2a1a0 * b2b1b0.
344 // r = 1 * a0b0 +
345 // 10 * (a1b0 + a0b1) +
346 // 100 * (a2b0 + a1b1 + a0b2) +
347 // 1000 * (a2b1 + a1b2) +
348 // 10000 * a2b2
349 //
350 // In the worst case we have to accumulate nb-digits products of digit*digit.
351 //
352 // Assert that the additional number of bits in a DoubleChunk are enough to
353 // sum up used_digits of Bigit*Bigit.
354 if ((1 << (2 * (kChunkSize - kBigitSize))) <= used_digits_) {
355 UNIMPLEMENTED();
356 }
357 DoubleChunk accumulator = 0;
358 // First shift the digits so we don't overwrite them.
359 int copy_offset = used_digits_;
360 for (int i = 0; i < used_digits_; ++i) {
361 bigits_[copy_offset + i] = bigits_[i];
362 }
363 // We have two loops to avoid some 'if's in the loop.
364 for (int i = 0; i < used_digits_; ++i) {
365 // Process temporary digit i with power i.
366 // The sum of the two indices must be equal to i.
367 int bigit_index1 = i;
368 int bigit_index2 = 0;
369 // Sum all of the sub-products.
370 while (bigit_index1 >= 0) {
371 Chunk chunk1 = bigits_[copy_offset + bigit_index1];
372 Chunk chunk2 = bigits_[copy_offset + bigit_index2];
373 accumulator += static_cast<DoubleChunk>(chunk1) * chunk2;
374 bigit_index1--;
375 bigit_index2++;
376 }
377 bigits_[i] = static_cast<Chunk>(accumulator) & kBigitMask;
378 accumulator >>= kBigitSize;
379 }
380 for (int i = used_digits_; i < product_length; ++i) {
381 int bigit_index1 = used_digits_ - 1;
382 int bigit_index2 = i - bigit_index1;
383 // Invariant: sum of both indices is again equal to i.
384 // Inner loop runs 0 times on last iteration, emptying accumulator.
385 while (bigit_index2 < used_digits_) {
386 Chunk chunk1 = bigits_[copy_offset + bigit_index1];
387 Chunk chunk2 = bigits_[copy_offset + bigit_index2];
388 accumulator += static_cast<DoubleChunk>(chunk1) * chunk2;
389 bigit_index1--;
390 bigit_index2++;
391 }
392 // The overwritten bigits_[i] will never be read in further loop iterations,
393 // because bigit_index1 and bigit_index2 are always greater
394 // than i - used_digits_.
395 bigits_[i] = static_cast<Chunk>(accumulator) & kBigitMask;
396 accumulator >>= kBigitSize;
397 }
398 // Since the result was guaranteed to lie inside the number the
399 // accumulator must be 0 now.
400 ASSERT(accumulator == 0);
401
402 // Don't forget to update the used_digits and the exponent.
403 used_digits_ = product_length;
404 exponent_ *= 2;
405 Clamp();
406}
407
408
409void Bignum::AssignPowerUInt16(uint16_t base, int power_exponent) {
410 ASSERT(base != 0);
411 ASSERT(power_exponent >= 0);
412 if (power_exponent == 0) {
413 AssignUInt16(1);
414 return;
415 }
416 Zero();
417 int shifts = 0;
418 // We expect base to be in range 2-32, and most often to be 10.
419 // It does not make much sense to implement different algorithms for counting
420 // the bits.
421 while ((base & 1) == 0) {
422 base >>= 1;
423 shifts++;
424 }
425 int bit_size = 0;
426 int tmp_base = base;
427 while (tmp_base != 0) {
428 tmp_base >>= 1;
429 bit_size++;
430 }
431 int final_size = bit_size * power_exponent;
432 // 1 extra bigit for the shifting, and one for rounded final_size.
433 EnsureCapacity(final_size / kBigitSize + 2);
434
435 // Left to Right exponentiation.
436 int mask = 1;
437 while (power_exponent >= mask) mask <<= 1;
438
439 // The mask is now pointing to the bit above the most significant 1-bit of
440 // power_exponent.
441 // Get rid of first 1-bit;
442 mask >>= 2;
443 uint64_t this_value = base;
444
445 bool delayed_multiplication = false;
446 const uint64_t max_32bits = 0xFFFFFFFF;
447 while (mask != 0 && this_value <= max_32bits) {
448 this_value = this_value * this_value;
449 // Verify that there is enough space in this_value to perform the
450 // multiplication. The first bit_size bits must be 0.
451 if ((power_exponent & mask) != 0) {
452 ASSERT(bit_size > 0);
453 uint64_t base_bits_mask =
454 ~((static_cast<uint64_t>(1) << (64 - bit_size)) - 1);
455 bool high_bits_zero = (this_value & base_bits_mask) == 0;
456 if (high_bits_zero) {
457 this_value *= base;
458 } else {
459 delayed_multiplication = true;
460 }
461 }
462 mask >>= 1;
463 }
464 AssignUInt64(this_value);
465 if (delayed_multiplication) {
466 MultiplyByUInt32(base);
467 }
468
469 // Now do the same thing as a bignum.
470 while (mask != 0) {
471 Square();
472 if ((power_exponent & mask) != 0) {
473 MultiplyByUInt32(base);
474 }
475 mask >>= 1;
476 }
477
478 // And finally add the saved shifts.
479 ShiftLeft(shifts * power_exponent);
480}
481
482
483// Precondition: this/other < 16bit.
484uint16_t Bignum::DivideModuloIntBignum(const Bignum& other) {
485 ASSERT(IsClamped());
486 ASSERT(other.IsClamped());
487 ASSERT(other.used_digits_ > 0);
488
489 // Easy case: if we have less digits than the divisor than the result is 0.
490 // Note: this handles the case where this == 0, too.
491 if (BigitLength() < other.BigitLength()) {
492 return 0;
493 }
494
495 Align(other);
496
497 uint16_t result = 0;
498
499 // Start by removing multiples of 'other' until both numbers have the same
500 // number of digits.
501 while (BigitLength() > other.BigitLength()) {
502 // This naive approach is extremely inefficient if `this` divided by other
503 // is big. This function is implemented for doubleToString where
504 // the result should be small (less than 10).
505 ASSERT(other.bigits_[other.used_digits_ - 1] >= ((1 << kBigitSize) / 16));
506 ASSERT(bigits_[used_digits_ - 1] < 0x10000);
507 // Remove the multiples of the first digit.
508 // Example this = 23 and other equals 9. -> Remove 2 multiples.
509 result += static_cast<uint16_t>(bigits_[used_digits_ - 1]);
510 SubtractTimes(other, bigits_[used_digits_ - 1]);
511 }
512
513 ASSERT(BigitLength() == other.BigitLength());
514
515 // Both bignums are at the same length now.
516 // Since other has more than 0 digits we know that the access to
517 // bigits_[used_digits_ - 1] is safe.
518 Chunk this_bigit = bigits_[used_digits_ - 1];
519 Chunk other_bigit = other.bigits_[other.used_digits_ - 1];
520
521 if (other.used_digits_ == 1) {
522 // Shortcut for easy (and common) case.
523 int quotient = this_bigit / other_bigit;
524 bigits_[used_digits_ - 1] = this_bigit - other_bigit * quotient;
525 ASSERT(quotient < 0x10000);
526 result += static_cast<uint16_t>(quotient);
527 Clamp();
528 return result;
529 }
530
531 int division_estimate = this_bigit / (other_bigit + 1);
532 ASSERT(division_estimate < 0x10000);
533 result += static_cast<uint16_t>(division_estimate);
534 SubtractTimes(other, division_estimate);
535
536 if (other_bigit * (division_estimate + 1) > this_bigit) {
537 // No need to even try to subtract. Even if other's remaining digits were 0
538 // another subtraction would be too much.
539 return result;
540 }
541
542 while (LessEqual(other, *this)) {
543 SubtractBignum(other);
544 result++;
545 }
546 return result;
547}
548
549
550template<typename S>
551static int SizeInHexChars(S number) {
552 ASSERT(number > 0);
553 int result = 0;
554 while (number != 0) {
555 number >>= 4;
556 result++;
557 }
558 return result;
559}
560
561
562static char HexCharOfValue(int value) {
563 ASSERT(0 <= value && value <= 16);
564 if (value < 10) return static_cast<char>(value + '0');
565 return static_cast<char>(value - 10 + 'A');
566}
567
568
569bool Bignum::ToHexString(char* buffer, int buffer_size) const {
570 ASSERT(IsClamped());
571 // Each bigit must be printable as separate hex-character.
572 ASSERT(kBigitSize % 4 == 0);
573 const int kHexCharsPerBigit = kBigitSize / 4;
574
575 if (used_digits_ == 0) {
576 if (buffer_size < 2) return false;
577 buffer[0] = '0';
578 buffer[1] = '\0';
579 return true;
580 }
581 // We add 1 for the terminating '\0' character.
582 int needed_chars = (BigitLength() - 1) * kHexCharsPerBigit +
583 SizeInHexChars(bigits_[used_digits_ - 1]) + 1;
584 if (needed_chars > buffer_size) return false;
585 int string_index = needed_chars - 1;
586 buffer[string_index--] = '\0';
587 for (int i = 0; i < exponent_; ++i) {
588 for (int j = 0; j < kHexCharsPerBigit; ++j) {
589 buffer[string_index--] = '0';
590 }
591 }
592 for (int i = 0; i < used_digits_ - 1; ++i) {
593 Chunk current_bigit = bigits_[i];
594 for (int j = 0; j < kHexCharsPerBigit; ++j) {
595 buffer[string_index--] = HexCharOfValue(current_bigit & 0xF);
596 current_bigit >>= 4;
597 }
598 }
599 // And finally the last bigit.
600 Chunk most_significant_bigit = bigits_[used_digits_ - 1];
601 while (most_significant_bigit != 0) {
602 buffer[string_index--] = HexCharOfValue(most_significant_bigit & 0xF);
603 most_significant_bigit >>= 4;
604 }
605 return true;
606}
607
608
609Bignum::Chunk Bignum::BigitAt(int index) const {
610 if (index >= BigitLength()) return 0;
611 if (index < exponent_) return 0;
612 return bigits_[index - exponent_];
613}
614
615
616int Bignum::Compare(const Bignum& a, const Bignum& b) {
617 ASSERT(a.IsClamped());
618 ASSERT(b.IsClamped());
619 int bigit_length_a = a.BigitLength();
620 int bigit_length_b = b.BigitLength();
621 if (bigit_length_a < bigit_length_b) return -1;
622 if (bigit_length_a > bigit_length_b) return +1;
623 for (int i = bigit_length_a - 1; i >= Min(a.exponent_, b.exponent_); --i) {
624 Chunk bigit_a = a.BigitAt(i);
625 Chunk bigit_b = b.BigitAt(i);
626 if (bigit_a < bigit_b) return -1;
627 if (bigit_a > bigit_b) return +1;
628 // Otherwise they are equal up to this digit. Try the next digit.
629 }
630 return 0;
631}
632
633
634int Bignum::PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c) {
635 ASSERT(a.IsClamped());
636 ASSERT(b.IsClamped());
637 ASSERT(c.IsClamped());
638 if (a.BigitLength() < b.BigitLength()) {
639 return PlusCompare(b, a, c);
640 }
641 if (a.BigitLength() + 1 < c.BigitLength()) return -1;
642 if (a.BigitLength() > c.BigitLength()) return +1;
643 // The exponent encodes 0-bigits. So if there are more 0-digits in 'a' than
644 // 'b' has digits, then the bigit-length of 'a'+'b' must be equal to the one
645 // of 'a'.
646 if (a.exponent_ >= b.BigitLength() && a.BigitLength() < c.BigitLength()) {
647 return -1;
648 }
649
650 Chunk borrow = 0;
651 // Starting at min_exponent all digits are == 0. So no need to compare them.
652 int min_exponent = Min(Min(a.exponent_, b.exponent_), c.exponent_);
653 for (int i = c.BigitLength() - 1; i >= min_exponent; --i) {
654 Chunk chunk_a = a.BigitAt(i);
655 Chunk chunk_b = b.BigitAt(i);
656 Chunk chunk_c = c.BigitAt(i);
657 Chunk sum = chunk_a + chunk_b;
658 if (sum > chunk_c + borrow) {
659 return +1;
660 } else {
661 borrow = chunk_c + borrow - sum;
662 if (borrow > 1) return -1;
663 borrow <<= kBigitSize;
664 }
665 }
666 if (borrow == 0) return 0;
667 return -1;
668}
669
670
671void Bignum::Clamp() {
672 while (used_digits_ > 0 && bigits_[used_digits_ - 1] == 0) {
673 used_digits_--;
674 }
675 if (used_digits_ == 0) {
676 // Zero.
677 exponent_ = 0;
678 }
679}
680
681
682bool Bignum::IsClamped() const {
683 return used_digits_ == 0 || bigits_[used_digits_ - 1] != 0;
684}
685
686
687void Bignum::Zero() {
688 for (int i = 0; i < used_digits_; ++i) {
689 bigits_[i] = 0;
690 }
691 used_digits_ = 0;
692 exponent_ = 0;
693}
694
695
696void Bignum::Align(const Bignum& other) {
697 if (exponent_ > other.exponent_) {
698 // If "X" represents a "hidden" digit (by the exponent) then we are in the
699 // following case (a == this, b == other):
700 // a: aaaaaaXXXX or a: aaaaaXXX
701 // b: bbbbbbX b: bbbbbbbbXX
702 // We replace some of the hidden digits (X) of a with 0 digits.
703 // a: aaaaaa000X or a: aaaaa0XX
704 int zero_digits = exponent_ - other.exponent_;
705 EnsureCapacity(used_digits_ + zero_digits);
706 for (int i = used_digits_ - 1; i >= 0; --i) {
707 bigits_[i + zero_digits] = bigits_[i];
708 }
709 for (int i = 0; i < zero_digits; ++i) {
710 bigits_[i] = 0;
711 }
712 used_digits_ += zero_digits;
713 exponent_ -= zero_digits;
714 ASSERT(used_digits_ >= 0);
715 ASSERT(exponent_ >= 0);
716 }
717}
718
719
720void Bignum::BigitsShiftLeft(int shift_amount) {
721 ASSERT(shift_amount < kBigitSize);
722 ASSERT(shift_amount >= 0);
723 Chunk carry = 0;
724 for (int i = 0; i < used_digits_; ++i) {
725 Chunk new_carry = bigits_[i] >> (kBigitSize - shift_amount);
726 bigits_[i] = ((bigits_[i] << shift_amount) + carry) & kBigitMask;
727 carry = new_carry;
728 }
729 if (carry != 0) {
730 bigits_[used_digits_] = carry;
731 used_digits_++;
732 }
733}
734
735
736void Bignum::SubtractTimes(const Bignum& other, int factor) {
737 ASSERT(exponent_ <= other.exponent_);
738 if (factor < 3) {
739 for (int i = 0; i < factor; ++i) {
740 SubtractBignum(other);
741 }
742 return;
743 }
744 Chunk borrow = 0;
745 int exponent_diff = other.exponent_ - exponent_;
746 for (int i = 0; i < other.used_digits_; ++i) {
747 DoubleChunk product = static_cast<DoubleChunk>(factor) * other.bigits_[i];
748 DoubleChunk remove = borrow + product;
749 Chunk difference = bigits_[i + exponent_diff] - (remove & kBigitMask);
750 bigits_[i + exponent_diff] = difference & kBigitMask;
751 borrow = static_cast<Chunk>((difference >> (kChunkSize - 1)) +
752 (remove >> kBigitSize));
753 }
754 for (int i = other.used_digits_ + exponent_diff; i < used_digits_; ++i) {
755 if (borrow == 0) return;
756 Chunk difference = bigits_[i] - borrow;
757 bigits_[i] = difference & kBigitMask;
758 borrow = difference >> (kChunkSize - 1);
759 }
760 Clamp();
761}
762
763
764} // namespace double_conversion
765} // namespace WTF
766