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Unified Diff: third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc

Issue 2700123003: DO NOT COMMIT: Results of running old (current) clang-format on Blink (Closed)
Patch Set: Created 3 years, 10 months ago
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Index: third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc
diff --git a/third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc b/third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc
index 0d79df4c3daf7febd5b87bce000a45261cd234ca..bf37b6d7894a2f238928dcafa20e1478e01f5fd6 100644
--- a/third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc
+++ b/third_party/WebKit/Source/wtf/dtoa/bignum-dtoa.cc
@@ -27,630 +27,653 @@
#include "bignum-dtoa.h"
+#include <math.h>
#include "bignum.h"
#include "double.h"
-#include <math.h>
namespace WTF {
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(double v,
- 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 = Double(v).Significand();
- bool is_even = (significand & 1) == 0;
- int exponent = Double(v).Exponent();
- 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);
- bool need_boundary_deltas = (mode == BIGNUM_DTOA_SHORTEST);
- InitialScaledStartValues(v, 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:
- 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;
- while (true) {
- 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;
- }
- }
+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(double v,
+ 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 = Double(v).Significand();
+ bool is_even = (significand & 1) == 0;
+ int exponent = Double(v).Exponent();
+ 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);
+ bool need_boundary_deltas = (mode == BIGNUM_DTOA_SHORTEST);
+ InitialScaledStartValues(v, 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:
+ 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;
+ while (true) {
+ 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);
}
-
-
- // 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++;
- }
- 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;
+ 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;
}
-
-
- // 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;
+ 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 {
- // 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);
+ 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;
}
-
-
- // 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 = 53;
- double estimate = ceil((exponent + kSignificandSize - 1) * k1Log10 - 1e-10);
- return static_cast<int>(estimate);
- }
-
-
- // See comments for InitialScaledStartValues.
- static void InitialScaledStartValuesPositiveExponent(
- double v, 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(Double(v).Significand());
- numerator->ShiftLeft(Double(v).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(Double(v).Exponent());
- // Same for delta_minus (with adjustments below if f == 2^p-1).
- delta_minus->AssignUInt16(1);
- delta_minus->ShiftLeft(Double(v).Exponent());
-
- // If the significand (without the hidden bit) is 0, then the lower
- // boundary is closer than just half a ulp (unit in the last place).
- // There is only one exception: if the next lower number is a denormal then
- // the distance is 1 ulp. This cannot be the case for exponent >= 0 (but we
- // have to test it in the other function where exponent < 0).
- uint64_t v_bits = Double(v).AsUint64();
- if ((v_bits & Double::kSignificandMask) == 0) {
- // 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
- }
- }
+ }
+}
+
+// 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++;
+ }
+ 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;
}
-
-
- // See comments for InitialScaledStartValues
- static void InitialScaledStartValuesNegativeExponentPositivePower(
- double v, int estimated_power, bool need_boundary_deltas,
- Bignum* numerator, Bignum* denominator,
- Bignum* delta_minus, Bignum* delta_plus) {
- uint64_t significand = Double(v).Significand();
- int exponent = Double(v).Exponent();
- // 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 (with adjustments below if f == 2^p-1).
- delta_minus->AssignUInt16(1);
-
- // If the significand (without the hidden bit) is 0, then the lower
- // boundary is closer than just one ulp (unit in the last place).
- // There is only one exception: if the next lower number is a denormal
- // then the distance is 1 ulp. Since the exponent is close to zero
- // (otherwise estimated_power would have been negative) this cannot happen
- // here either.
- uint64_t v_bits = Double(v).AsUint64();
- if ((v_bits & Double::kSignificandMask) == 0) {
- // The lower boundary is closer at half the distance of "normal" numbers.
- // Increase the denominator and adapt all but the delta_minus.
- denominator->ShiftLeft(1); // *2
- numerator->ShiftLeft(1); // *2
- delta_plus->ShiftLeft(1); // *2
- }
- }
+ 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 = 53;
+ double estimate = ceil((exponent + kSignificandSize - 1) * k1Log10 - 1e-10);
+ return static_cast<int>(estimate);
+}
+
+// See comments for InitialScaledStartValues.
+static void InitialScaledStartValuesPositiveExponent(double v,
+ 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(Double(v).Significand());
+ numerator->ShiftLeft(Double(v).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(Double(v).Exponent());
+ // Same for delta_minus (with adjustments below if f == 2^p-1).
+ delta_minus->AssignUInt16(1);
+ delta_minus->ShiftLeft(Double(v).Exponent());
+
+ // If the significand (without the hidden bit) is 0, then the lower
+ // boundary is closer than just half a ulp (unit in the last place).
+ // There is only one exception: if the next lower number is a denormal then
+ // the distance is 1 ulp. This cannot be the case for exponent >= 0 (but we
+ // have to test it in the other function where exponent < 0).
+ uint64_t v_bits = Double(v).AsUint64();
+ if ((v_bits & Double::kSignificandMask) == 0) {
+ // 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
}
-
-
- // See comments for InitialScaledStartValues
- static void InitialScaledStartValuesNegativeExponentNegativePower(
- double v, int estimated_power, bool need_boundary_deltas,
- Bignum* numerator, Bignum* denominator,
- Bignum* delta_minus, Bignum* delta_plus) {
- const uint64_t kMinimalNormalizedExponent =
- UINT64_2PART_C(0x00100000, 00000000);
- uint64_t significand = Double(v).Significand();
- int exponent = Double(v).Exponent();
- // 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 special case where the lower boundary is twice as close.
- // This time we have to look out for the exception too.
- uint64_t v_bits = Double(v).AsUint64();
- if ((v_bits & Double::kSignificandMask) == 0 &&
- // The only exception where a significand == 0 has its boundaries at
- // "normal" distances:
- (v_bits & Double::kExponentMask) != kMinimalNormalizedExponent) {
- numerator->ShiftLeft(1); // *2
- denominator->ShiftLeft(1); // *2
- delta_plus->ShiftLeft(1); // *2
- }
- }
+ }
+}
+
+// See comments for InitialScaledStartValues
+static void InitialScaledStartValuesNegativeExponentPositivePower(
+ double v,
+ int estimated_power,
+ bool need_boundary_deltas,
+ Bignum* numerator,
+ Bignum* denominator,
+ Bignum* delta_minus,
+ Bignum* delta_plus) {
+ uint64_t significand = Double(v).Significand();
+ int exponent = Double(v).Exponent();
+ // 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 (with adjustments below if f == 2^p-1).
+ delta_minus->AssignUInt16(1);
+
+ // If the significand (without the hidden bit) is 0, then the lower
+ // boundary is closer than just one ulp (unit in the last place).
+ // There is only one exception: if the next lower number is a denormal
+ // then the distance is 1 ulp. Since the exponent is close to zero
+ // (otherwise estimated_power would have been negative) this cannot happen
+ // here either.
+ uint64_t v_bits = Double(v).AsUint64();
+ if ((v_bits & Double::kSignificandMask) == 0) {
+ // The lower boundary is closer at half the distance of "normal" numbers.
+ // Increase the denominator and adapt all but the delta_minus.
+ denominator->ShiftLeft(1); // *2
+ numerator->ShiftLeft(1); // *2
+ delta_plus->ShiftLeft(1); // *2
}
-
-
- // 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 need_boundary_deltas is set.
- static void InitialScaledStartValues(double v,
- int estimated_power,
- bool need_boundary_deltas,
- Bignum* numerator,
- Bignum* denominator,
- Bignum* delta_minus,
- Bignum* delta_plus) {
- if (Double(v).Exponent() >= 0) {
- InitialScaledStartValuesPositiveExponent(
- v, estimated_power, need_boundary_deltas,
- numerator, denominator, delta_minus, delta_plus);
- } else if (estimated_power >= 0) {
- InitialScaledStartValuesNegativeExponentPositivePower(
- v, estimated_power, need_boundary_deltas,
- numerator, denominator, delta_minus, delta_plus);
- } else {
- InitialScaledStartValuesNegativeExponentNegativePower(
- v, estimated_power, need_boundary_deltas,
- numerator, denominator, delta_minus, delta_plus);
- }
+ }
+}
+
+// See comments for InitialScaledStartValues
+static void InitialScaledStartValuesNegativeExponentNegativePower(
+ double v,
+ int estimated_power,
+ bool need_boundary_deltas,
+ Bignum* numerator,
+ Bignum* denominator,
+ Bignum* delta_minus,
+ Bignum* delta_plus) {
+ const uint64_t kMinimalNormalizedExponent =
+ UINT64_2PART_C(0x00100000, 00000000);
+ uint64_t significand = Double(v).Significand();
+ int exponent = Double(v).Exponent();
+ // 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 special case where the lower boundary is twice as close.
+ // This time we have to look out for the exception too.
+ uint64_t v_bits = Double(v).AsUint64();
+ if ((v_bits & Double::kSignificandMask) == 0 &&
+ // The only exception where a significand == 0 has its boundaries at
+ // "normal" distances:
+ (v_bits & Double::kExponentMask) != kMinimalNormalizedExponent) {
+ numerator->ShiftLeft(1); // *2
+ denominator->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();
- }
- }
+ }
+}
+
+// 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 need_boundary_deltas is set.
+static void InitialScaledStartValues(double v,
+ int estimated_power,
+ bool need_boundary_deltas,
+ Bignum* numerator,
+ Bignum* denominator,
+ Bignum* delta_minus,
+ Bignum* delta_plus) {
+ if (Double(v).Exponent() >= 0) {
+ InitialScaledStartValuesPositiveExponent(
+ v, estimated_power, need_boundary_deltas, numerator, denominator,
+ delta_minus, delta_plus);
+ } else if (estimated_power >= 0) {
+ InitialScaledStartValuesNegativeExponentPositivePower(
+ v, estimated_power, need_boundary_deltas, numerator, denominator,
+ delta_minus, delta_plus);
+ } else {
+ InitialScaledStartValuesNegativeExponentNegativePower(
+ v, estimated_power, need_boundary_deltas, numerator, denominator,
+ delta_minus, delta_plus);
+ }
+}
+
+// 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
-} // namespace WTF
+} // namespace WTF
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