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Diffstat (limited to 'src/3rdparty/double-conversion/bignum-dtoa.cc')
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diff --git a/src/3rdparty/double-conversion/bignum-dtoa.cc b/src/3rdparty/double-conversion/bignum-dtoa.cc new file mode 100644 index 0000000000..f1ad7a5ae8 --- /dev/null +++ b/src/3rdparty/double-conversion/bignum-dtoa.cc @@ -0,0 +1,641 @@ +// Copyright 2010 the V8 project authors. All rights reserved. +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are +// met: +// +// * Redistributions of source code must retain the above copyright +// notice, this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above +// copyright notice, this list of conditions and the following +// disclaimer in the documentation and/or other materials provided +// with the distribution. +// * Neither the name of Google Inc. nor the names of its +// contributors may be used to endorse or promote products derived +// from this software without specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +#include <math.h> + +#include "bignum-dtoa.h" + +#include "bignum.h" +#include "ieee.h" + +namespace double_conversion { + +static int NormalizedExponent(uint64_t significand, int exponent) { + ASSERT(significand != 0); + while ((significand & Double::kHiddenBit) == 0) { + significand = significand << 1; + exponent = exponent - 1; + } + return exponent; +} + + +// Forward declarations: +// Returns an estimation of k such that 10^(k-1) <= v < 10^k. +static int EstimatePower(int exponent); +// Computes v / 10^estimated_power exactly, as a ratio of two bignums, numerator +// and denominator. +static void InitialScaledStartValues(uint64_t significand, + int exponent, + bool lower_boundary_is_closer, + int estimated_power, + bool need_boundary_deltas, + Bignum* numerator, + Bignum* denominator, + Bignum* delta_minus, + Bignum* delta_plus); +// Multiplies numerator/denominator so that its values lies in the range 1-10. +// Returns decimal_point s.t. +// v = numerator'/denominator' * 10^(decimal_point-1) +// where numerator' and denominator' are the values of numerator and +// denominator after the call to this function. +static void FixupMultiply10(int estimated_power, bool is_even, + int* decimal_point, + Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus); +// Generates digits from the left to the right and stops when the generated +// digits yield the shortest decimal representation of v. +static void GenerateShortestDigits(Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus, + bool is_even, + Vector<char> buffer, int* length); +// Generates 'requested_digits' after the decimal point. +static void BignumToFixed(int requested_digits, int* decimal_point, + Bignum* numerator, Bignum* denominator, + Vector<char>(buffer), int* length); +// Generates 'count' digits of numerator/denominator. +// Once 'count' digits have been produced rounds the result depending on the +// remainder (remainders of exactly .5 round upwards). Might update the +// decimal_point when rounding up (for example for 0.9999). +static void GenerateCountedDigits(int count, int* decimal_point, + Bignum* numerator, Bignum* denominator, + Vector<char>(buffer), int* length); + + +void BignumDtoa(double v, BignumDtoaMode mode, int requested_digits, + Vector<char> buffer, int* length, int* decimal_point) { + ASSERT(v > 0); + ASSERT(!Double(v).IsSpecial()); + uint64_t significand; + int exponent; + bool lower_boundary_is_closer; + if (mode == BIGNUM_DTOA_SHORTEST_SINGLE) { + float f = static_cast<float>(v); + ASSERT(f == v); + significand = Single(f).Significand(); + exponent = Single(f).Exponent(); + lower_boundary_is_closer = Single(f).LowerBoundaryIsCloser(); + } else { + significand = Double(v).Significand(); + exponent = Double(v).Exponent(); + lower_boundary_is_closer = Double(v).LowerBoundaryIsCloser(); + } + bool need_boundary_deltas = + (mode == BIGNUM_DTOA_SHORTEST || mode == BIGNUM_DTOA_SHORTEST_SINGLE); + + bool is_even = (significand & 1) == 0; + int normalized_exponent = NormalizedExponent(significand, exponent); + // estimated_power might be too low by 1. + int estimated_power = EstimatePower(normalized_exponent); + + // Shortcut for Fixed. + // The requested digits correspond to the digits after the point. If the + // number is much too small, then there is no need in trying to get any + // digits. + if (mode == BIGNUM_DTOA_FIXED && -estimated_power - 1 > requested_digits) { + buffer[0] = '\0'; + *length = 0; + // Set decimal-point to -requested_digits. This is what Gay does. + // Note that it should not have any effect anyways since the string is + // empty. + *decimal_point = -requested_digits; + return; + } + + Bignum numerator; + Bignum denominator; + Bignum delta_minus; + Bignum delta_plus; + // Make sure the bignum can grow large enough. The smallest double equals + // 4e-324. In this case the denominator needs fewer than 324*4 binary digits. + // The maximum double is 1.7976931348623157e308 which needs fewer than + // 308*4 binary digits. + ASSERT(Bignum::kMaxSignificantBits >= 324*4); + InitialScaledStartValues(significand, exponent, lower_boundary_is_closer, + estimated_power, need_boundary_deltas, + &numerator, &denominator, + &delta_minus, &delta_plus); + // We now have v = (numerator / denominator) * 10^estimated_power. + FixupMultiply10(estimated_power, is_even, decimal_point, + &numerator, &denominator, + &delta_minus, &delta_plus); + // We now have v = (numerator / denominator) * 10^(decimal_point-1), and + // 1 <= (numerator + delta_plus) / denominator < 10 + switch (mode) { + case BIGNUM_DTOA_SHORTEST: + case BIGNUM_DTOA_SHORTEST_SINGLE: + GenerateShortestDigits(&numerator, &denominator, + &delta_minus, &delta_plus, + is_even, buffer, length); + break; + case BIGNUM_DTOA_FIXED: + BignumToFixed(requested_digits, decimal_point, + &numerator, &denominator, + buffer, length); + break; + case BIGNUM_DTOA_PRECISION: + GenerateCountedDigits(requested_digits, decimal_point, + &numerator, &denominator, + buffer, length); + break; + default: + UNREACHABLE(); + } + buffer[*length] = '\0'; +} + + +// The procedure starts generating digits from the left to the right and stops +// when the generated digits yield the shortest decimal representation of v. A +// decimal representation of v is a number lying closer to v than to any other +// double, so it converts to v when read. +// +// This is true if d, the decimal representation, is between m- and m+, the +// upper and lower boundaries. d must be strictly between them if !is_even. +// m- := (numerator - delta_minus) / denominator +// m+ := (numerator + delta_plus) / denominator +// +// Precondition: 0 <= (numerator+delta_plus) / denominator < 10. +// If 1 <= (numerator+delta_plus) / denominator < 10 then no leading 0 digit +// will be produced. This should be the standard precondition. +static void GenerateShortestDigits(Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus, + bool is_even, + Vector<char> buffer, int* length) { + // Small optimization: if delta_minus and delta_plus are the same just reuse + // one of the two bignums. + if (Bignum::Equal(*delta_minus, *delta_plus)) { + delta_plus = delta_minus; + } + *length = 0; + for (;;) { + uint16_t digit; + digit = numerator->DivideModuloIntBignum(*denominator); + ASSERT(digit <= 9); // digit is a uint16_t and therefore always positive. + // digit = numerator / denominator (integer division). + // numerator = numerator % denominator. + buffer[(*length)++] = static_cast<char>(digit + '0'); + + // Can we stop already? + // If the remainder of the division is less than the distance to the lower + // boundary we can stop. In this case we simply round down (discarding the + // remainder). + // Similarly we test if we can round up (using the upper boundary). + bool in_delta_room_minus; + bool in_delta_room_plus; + if (is_even) { + in_delta_room_minus = Bignum::LessEqual(*numerator, *delta_minus); + } else { + in_delta_room_minus = Bignum::Less(*numerator, *delta_minus); + } + if (is_even) { + in_delta_room_plus = + Bignum::PlusCompare(*numerator, *delta_plus, *denominator) >= 0; + } else { + in_delta_room_plus = + Bignum::PlusCompare(*numerator, *delta_plus, *denominator) > 0; + } + if (!in_delta_room_minus && !in_delta_room_plus) { + // Prepare for next iteration. + numerator->Times10(); + delta_minus->Times10(); + // We optimized delta_plus to be equal to delta_minus (if they share the + // same value). So don't multiply delta_plus if they point to the same + // object. + if (delta_minus != delta_plus) { + delta_plus->Times10(); + } + } else if (in_delta_room_minus && in_delta_room_plus) { + // Let's see if 2*numerator < denominator. + // If yes, then the next digit would be < 5 and we can round down. + int compare = Bignum::PlusCompare(*numerator, *numerator, *denominator); + if (compare < 0) { + // Remaining digits are less than .5. -> Round down (== do nothing). + } else if (compare > 0) { + // Remaining digits are more than .5 of denominator. -> Round up. + // Note that the last digit could not be a '9' as otherwise the whole + // loop would have stopped earlier. + // We still have an assert here in case the preconditions were not + // satisfied. + ASSERT(buffer[(*length) - 1] != '9'); + buffer[(*length) - 1]++; + } else { + // Halfway case. + // TODO(floitsch): need a way to solve half-way cases. + // For now let's round towards even (since this is what Gay seems to + // do). + + if ((buffer[(*length) - 1] - '0') % 2 == 0) { + // Round down => Do nothing. + } else { + ASSERT(buffer[(*length) - 1] != '9'); + buffer[(*length) - 1]++; + } + } + return; + } else if (in_delta_room_minus) { + // Round down (== do nothing). + return; + } else { // in_delta_room_plus + // Round up. + // Note again that the last digit could not be '9' since this would have + // stopped the loop earlier. + // We still have an ASSERT here, in case the preconditions were not + // satisfied. + ASSERT(buffer[(*length) -1] != '9'); + buffer[(*length) - 1]++; + return; + } + } +} + + +// Let v = numerator / denominator < 10. +// Then we generate 'count' digits of d = x.xxxxx... (without the decimal point) +// from left to right. Once 'count' digits have been produced we decide wether +// to round up or down. Remainders of exactly .5 round upwards. Numbers such +// as 9.999999 propagate a carry all the way, and change the +// exponent (decimal_point), when rounding upwards. +static void GenerateCountedDigits(int count, int* decimal_point, + Bignum* numerator, Bignum* denominator, + Vector<char> buffer, int* length) { + ASSERT(count >= 0); + for (int i = 0; i < count - 1; ++i) { + uint16_t digit; + digit = numerator->DivideModuloIntBignum(*denominator); + ASSERT(digit <= 9); // digit is a uint16_t and therefore always positive. + // digit = numerator / denominator (integer division). + // numerator = numerator % denominator. + buffer[i] = static_cast<char>(digit + '0'); + // Prepare for next iteration. + numerator->Times10(); + } + // Generate the last digit. + uint16_t digit; + digit = numerator->DivideModuloIntBignum(*denominator); + if (Bignum::PlusCompare(*numerator, *numerator, *denominator) >= 0) { + digit++; + } + ASSERT(digit <= 10); + buffer[count - 1] = static_cast<char>(digit + '0'); + // Correct bad digits (in case we had a sequence of '9's). Propagate the + // carry until we hat a non-'9' or til we reach the first digit. + for (int i = count - 1; i > 0; --i) { + if (buffer[i] != '0' + 10) break; + buffer[i] = '0'; + buffer[i - 1]++; + } + if (buffer[0] == '0' + 10) { + // Propagate a carry past the top place. + buffer[0] = '1'; + (*decimal_point)++; + } + *length = count; +} + + +// Generates 'requested_digits' after the decimal point. It might omit +// trailing '0's. If the input number is too small then no digits at all are +// generated (ex.: 2 fixed digits for 0.00001). +// +// Input verifies: 1 <= (numerator + delta) / denominator < 10. +static void BignumToFixed(int requested_digits, int* decimal_point, + Bignum* numerator, Bignum* denominator, + Vector<char>(buffer), int* length) { + // Note that we have to look at more than just the requested_digits, since + // a number could be rounded up. Example: v=0.5 with requested_digits=0. + // Even though the power of v equals 0 we can't just stop here. + if (-(*decimal_point) > requested_digits) { + // The number is definitively too small. + // Ex: 0.001 with requested_digits == 1. + // Set decimal-point to -requested_digits. This is what Gay does. + // Note that it should not have any effect anyways since the string is + // empty. + *decimal_point = -requested_digits; + *length = 0; + return; + } else if (-(*decimal_point) == requested_digits) { + // We only need to verify if the number rounds down or up. + // Ex: 0.04 and 0.06 with requested_digits == 1. + ASSERT(*decimal_point == -requested_digits); + // Initially the fraction lies in range (1, 10]. Multiply the denominator + // by 10 so that we can compare more easily. + denominator->Times10(); + if (Bignum::PlusCompare(*numerator, *numerator, *denominator) >= 0) { + // If the fraction is >= 0.5 then we have to include the rounded + // digit. + buffer[0] = '1'; + *length = 1; + (*decimal_point)++; + } else { + // Note that we caught most of similar cases earlier. + *length = 0; + } + return; + } else { + // The requested digits correspond to the digits after the point. + // The variable 'needed_digits' includes the digits before the point. + int needed_digits = (*decimal_point) + requested_digits; + GenerateCountedDigits(needed_digits, decimal_point, + numerator, denominator, + buffer, length); + } +} + + +// Returns an estimation of k such that 10^(k-1) <= v < 10^k where +// v = f * 2^exponent and 2^52 <= f < 2^53. +// v is hence a normalized double with the given exponent. The output is an +// approximation for the exponent of the decimal approimation .digits * 10^k. +// +// The result might undershoot by 1 in which case 10^k <= v < 10^k+1. +// Note: this property holds for v's upper boundary m+ too. +// 10^k <= m+ < 10^k+1. +// (see explanation below). +// +// Examples: +// EstimatePower(0) => 16 +// EstimatePower(-52) => 0 +// +// Note: e >= 0 => EstimatedPower(e) > 0. No similar claim can be made for e<0. +static int EstimatePower(int exponent) { + // This function estimates log10 of v where v = f*2^e (with e == exponent). + // Note that 10^floor(log10(v)) <= v, but v <= 10^ceil(log10(v)). + // Note that f is bounded by its container size. Let p = 53 (the double's + // significand size). Then 2^(p-1) <= f < 2^p. + // + // Given that log10(v) == log2(v)/log2(10) and e+(len(f)-1) is quite close + // to log2(v) the function is simplified to (e+(len(f)-1)/log2(10)). + // The computed number undershoots by less than 0.631 (when we compute log3 + // and not log10). + // + // Optimization: since we only need an approximated result this computation + // can be performed on 64 bit integers. On x86/x64 architecture the speedup is + // not really measurable, though. + // + // Since we want to avoid overshooting we decrement by 1e10 so that + // floating-point imprecisions don't affect us. + // + // Explanation for v's boundary m+: the computation takes advantage of + // the fact that 2^(p-1) <= f < 2^p. Boundaries still satisfy this requirement + // (even for denormals where the delta can be much more important). + + const double k1Log10 = 0.30102999566398114; // 1/lg(10) + + // For doubles len(f) == 53 (don't forget the hidden bit). + const int kSignificandSize = Double::kSignificandSize; + double estimate = ceil((exponent + kSignificandSize - 1) * k1Log10 - 1e-10); + return static_cast<int>(estimate); +} + + +// See comments for InitialScaledStartValues. +static void InitialScaledStartValuesPositiveExponent( + uint64_t significand, int exponent, + int estimated_power, bool need_boundary_deltas, + Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus) { + // A positive exponent implies a positive power. + ASSERT(estimated_power >= 0); + // Since the estimated_power is positive we simply multiply the denominator + // by 10^estimated_power. + + // numerator = v. + numerator->AssignUInt64(significand); + numerator->ShiftLeft(exponent); + // denominator = 10^estimated_power. + denominator->AssignPowerUInt16(10, estimated_power); + + if (need_boundary_deltas) { + // Introduce a common denominator so that the deltas to the boundaries are + // integers. + denominator->ShiftLeft(1); + numerator->ShiftLeft(1); + // Let v = f * 2^e, then m+ - v = 1/2 * 2^e; With the common + // denominator (of 2) delta_plus equals 2^e. + delta_plus->AssignUInt16(1); + delta_plus->ShiftLeft(exponent); + // Same for delta_minus. The adjustments if f == 2^p-1 are done later. + delta_minus->AssignUInt16(1); + delta_minus->ShiftLeft(exponent); + } +} + + +// See comments for InitialScaledStartValues +static void InitialScaledStartValuesNegativeExponentPositivePower( + uint64_t significand, int exponent, + int estimated_power, bool need_boundary_deltas, + Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus) { + // v = f * 2^e with e < 0, and with estimated_power >= 0. + // This means that e is close to 0 (have a look at how estimated_power is + // computed). + + // numerator = significand + // since v = significand * 2^exponent this is equivalent to + // numerator = v * / 2^-exponent + numerator->AssignUInt64(significand); + // denominator = 10^estimated_power * 2^-exponent (with exponent < 0) + denominator->AssignPowerUInt16(10, estimated_power); + denominator->ShiftLeft(-exponent); + + if (need_boundary_deltas) { + // Introduce a common denominator so that the deltas to the boundaries are + // integers. + denominator->ShiftLeft(1); + numerator->ShiftLeft(1); + // Let v = f * 2^e, then m+ - v = 1/2 * 2^e; With the common + // denominator (of 2) delta_plus equals 2^e. + // Given that the denominator already includes v's exponent the distance + // to the boundaries is simply 1. + delta_plus->AssignUInt16(1); + // Same for delta_minus. The adjustments if f == 2^p-1 are done later. + delta_minus->AssignUInt16(1); + } +} + + +// See comments for InitialScaledStartValues +static void InitialScaledStartValuesNegativeExponentNegativePower( + uint64_t significand, int exponent, + int estimated_power, bool need_boundary_deltas, + Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus) { + // Instead of multiplying the denominator with 10^estimated_power we + // multiply all values (numerator and deltas) by 10^-estimated_power. + + // Use numerator as temporary container for power_ten. + Bignum* power_ten = numerator; + power_ten->AssignPowerUInt16(10, -estimated_power); + + if (need_boundary_deltas) { + // Since power_ten == numerator we must make a copy of 10^estimated_power + // before we complete the computation of the numerator. + // delta_plus = delta_minus = 10^estimated_power + delta_plus->AssignBignum(*power_ten); + delta_minus->AssignBignum(*power_ten); + } + + // numerator = significand * 2 * 10^-estimated_power + // since v = significand * 2^exponent this is equivalent to + // numerator = v * 10^-estimated_power * 2 * 2^-exponent. + // Remember: numerator has been abused as power_ten. So no need to assign it + // to itself. + ASSERT(numerator == power_ten); + numerator->MultiplyByUInt64(significand); + + // denominator = 2 * 2^-exponent with exponent < 0. + denominator->AssignUInt16(1); + denominator->ShiftLeft(-exponent); + + if (need_boundary_deltas) { + // Introduce a common denominator so that the deltas to the boundaries are + // integers. + numerator->ShiftLeft(1); + denominator->ShiftLeft(1); + // With this shift the boundaries have their correct value, since + // delta_plus = 10^-estimated_power, and + // delta_minus = 10^-estimated_power. + // These assignments have been done earlier. + // The adjustments if f == 2^p-1 (lower boundary is closer) are done later. + } +} + + +// Let v = significand * 2^exponent. +// Computes v / 10^estimated_power exactly, as a ratio of two bignums, numerator +// and denominator. The functions GenerateShortestDigits and +// GenerateCountedDigits will then convert this ratio to its decimal +// representation d, with the required accuracy. +// Then d * 10^estimated_power is the representation of v. +// (Note: the fraction and the estimated_power might get adjusted before +// generating the decimal representation.) +// +// The initial start values consist of: +// - a scaled numerator: s.t. numerator/denominator == v / 10^estimated_power. +// - a scaled (common) denominator. +// optionally (used by GenerateShortestDigits to decide if it has the shortest +// decimal converting back to v): +// - v - m-: the distance to the lower boundary. +// - m+ - v: the distance to the upper boundary. +// +// v, m+, m-, and therefore v - m- and m+ - v all share the same denominator. +// +// Let ep == estimated_power, then the returned values will satisfy: +// v / 10^ep = numerator / denominator. +// v's boundarys m- and m+: +// m- / 10^ep == v / 10^ep - delta_minus / denominator +// m+ / 10^ep == v / 10^ep + delta_plus / denominator +// Or in other words: +// m- == v - delta_minus * 10^ep / denominator; +// m+ == v + delta_plus * 10^ep / denominator; +// +// Since 10^(k-1) <= v < 10^k (with k == estimated_power) +// or 10^k <= v < 10^(k+1) +// we then have 0.1 <= numerator/denominator < 1 +// or 1 <= numerator/denominator < 10 +// +// It is then easy to kickstart the digit-generation routine. +// +// The boundary-deltas are only filled if the mode equals BIGNUM_DTOA_SHORTEST +// or BIGNUM_DTOA_SHORTEST_SINGLE. + +static void InitialScaledStartValues(uint64_t significand, + int exponent, + bool lower_boundary_is_closer, + int estimated_power, + bool need_boundary_deltas, + Bignum* numerator, + Bignum* denominator, + Bignum* delta_minus, + Bignum* delta_plus) { + if (exponent >= 0) { + InitialScaledStartValuesPositiveExponent( + significand, exponent, estimated_power, need_boundary_deltas, + numerator, denominator, delta_minus, delta_plus); + } else if (estimated_power >= 0) { + InitialScaledStartValuesNegativeExponentPositivePower( + significand, exponent, estimated_power, need_boundary_deltas, + numerator, denominator, delta_minus, delta_plus); + } else { + InitialScaledStartValuesNegativeExponentNegativePower( + significand, exponent, estimated_power, need_boundary_deltas, + numerator, denominator, delta_minus, delta_plus); + } + + if (need_boundary_deltas && lower_boundary_is_closer) { + // The lower boundary is closer at half the distance of "normal" numbers. + // Increase the common denominator and adapt all but the delta_minus. + denominator->ShiftLeft(1); // *2 + numerator->ShiftLeft(1); // *2 + delta_plus->ShiftLeft(1); // *2 + } +} + + +// This routine multiplies numerator/denominator so that its values lies in the +// range 1-10. That is after a call to this function we have: +// 1 <= (numerator + delta_plus) /denominator < 10. +// Let numerator the input before modification and numerator' the argument +// after modification, then the output-parameter decimal_point is such that +// numerator / denominator * 10^estimated_power == +// numerator' / denominator' * 10^(decimal_point - 1) +// In some cases estimated_power was too low, and this is already the case. We +// then simply adjust the power so that 10^(k-1) <= v < 10^k (with k == +// estimated_power) but do not touch the numerator or denominator. +// Otherwise the routine multiplies the numerator and the deltas by 10. +static void FixupMultiply10(int estimated_power, bool is_even, + int* decimal_point, + Bignum* numerator, Bignum* denominator, + Bignum* delta_minus, Bignum* delta_plus) { + bool in_range; + if (is_even) { + // For IEEE doubles half-way cases (in decimal system numbers ending with 5) + // are rounded to the closest floating-point number with even significand. + in_range = Bignum::PlusCompare(*numerator, *delta_plus, *denominator) >= 0; + } else { + in_range = Bignum::PlusCompare(*numerator, *delta_plus, *denominator) > 0; + } + if (in_range) { + // Since numerator + delta_plus >= denominator we already have + // 1 <= numerator/denominator < 10. Simply update the estimated_power. + *decimal_point = estimated_power + 1; + } else { + *decimal_point = estimated_power; + numerator->Times10(); + if (Bignum::Equal(*delta_minus, *delta_plus)) { + delta_minus->Times10(); + delta_plus->AssignBignum(*delta_minus); + } else { + delta_minus->Times10(); + delta_plus->Times10(); + } + } +} + +} // namespace double_conversion |