Update V8 to r5716 as required by WebKit r70949
Change-Id: I0d5cd05bb0427af33e5c9f6efdc209366a32bde3
diff --git a/src/strtod.cc b/src/strtod.cc
index ae278bd..0ed1b0d 100644
--- a/src/strtod.cc
+++ b/src/strtod.cc
@@ -31,7 +31,8 @@
#include "v8.h"
#include "strtod.h"
-// #include "cached-powers.h"
+#include "cached-powers.h"
+#include "double.h"
namespace v8 {
namespace internal {
@@ -40,9 +41,9 @@
// Any integer with at most 15 decimal digits will hence fit into a double
// (which has a 53bit significand) without loss of precision.
static const int kMaxExactDoubleIntegerDecimalDigits = 15;
-// 2^64 = 18446744073709551616
-// Any integer with at most 19 digits will hence fit into a 64bit datatype.
+// 2^64 = 18446744073709551616 > 10^19
static const int kMaxUint64DecimalDigits = 19;
+
// Max double: 1.7976931348623157 x 10^308
// Min non-zero double: 4.9406564584124654 x 10^-324
// Any x >= 10^309 is interpreted as +infinity.
@@ -52,6 +53,10 @@
static const int kMaxDecimalPower = 309;
static const int kMinDecimalPower = -324;
+// 2^64 = 18446744073709551616
+static const uint64_t kMaxUint64 = V8_2PART_UINT64_C(0xFFFFFFFF, FFFFFFFF);
+
+
static const double exact_powers_of_ten[] = {
1.0, // 10^0
10.0,
@@ -120,7 +125,7 @@
static Vector<const char> TrimLeadingZeros(Vector<const char> buffer) {
for (int i = 0; i < buffer.length(); i++) {
if (buffer[i] != '0') {
- return Vector<const char>(buffer.start() + i, buffer.length() - i);
+ return buffer.SubVector(i, buffer.length());
}
}
return Vector<const char>(buffer.start(), 0);
@@ -130,25 +135,57 @@
static Vector<const char> TrimTrailingZeros(Vector<const char> buffer) {
for (int i = buffer.length() - 1; i >= 0; --i) {
if (buffer[i] != '0') {
- return Vector<const char>(buffer.start(), i + 1);
+ return buffer.SubVector(0, i + 1);
}
}
return Vector<const char>(buffer.start(), 0);
}
-uint64_t ReadUint64(Vector<const char> buffer) {
- ASSERT(buffer.length() <= kMaxUint64DecimalDigits);
+// Reads digits from the buffer and converts them to a uint64.
+// Reads in as many digits as fit into a uint64.
+// When the string starts with "1844674407370955161" no further digit is read.
+// Since 2^64 = 18446744073709551616 it would still be possible read another
+// digit if it was less or equal than 6, but this would complicate the code.
+static uint64_t ReadUint64(Vector<const char> buffer,
+ int* number_of_read_digits) {
uint64_t result = 0;
- for (int i = 0; i < buffer.length(); ++i) {
- int digit = buffer[i] - '0';
+ int i = 0;
+ while (i < buffer.length() && result <= (kMaxUint64 / 10 - 1)) {
+ int digit = buffer[i++] - '0';
ASSERT(0 <= digit && digit <= 9);
result = 10 * result + digit;
}
+ *number_of_read_digits = i;
return result;
}
+// Reads a DiyFp from the buffer.
+// The returned DiyFp is not necessarily normalized.
+// If remaining_decimals is zero then the returned DiyFp is accurate.
+// Otherwise it has been rounded and has error of at most 1/2 ulp.
+static void ReadDiyFp(Vector<const char> buffer,
+ DiyFp* result,
+ int* remaining_decimals) {
+ int read_digits;
+ uint64_t significand = ReadUint64(buffer, &read_digits);
+ if (buffer.length() == read_digits) {
+ *result = DiyFp(significand, 0);
+ *remaining_decimals = 0;
+ } else {
+ // Round the significand.
+ if (buffer[read_digits] >= '5') {
+ significand++;
+ }
+ // Compute the binary exponent.
+ int exponent = 0;
+ *result = DiyFp(significand, exponent);
+ *remaining_decimals = buffer.length() - read_digits;
+ }
+}
+
+
static bool DoubleStrtod(Vector<const char> trimmed,
int exponent,
double* result) {
@@ -162,6 +199,7 @@
return false;
#endif
if (trimmed.length() <= kMaxExactDoubleIntegerDecimalDigits) {
+ int read_digits;
// The trimmed input fits into a double.
// If the 10^exponent (resp. 10^-exponent) fits into a double too then we
// can compute the result-double simply by multiplying (resp. dividing) the
@@ -170,13 +208,15 @@
// return the best possible approximation.
if (exponent < 0 && -exponent < kExactPowersOfTenSize) {
// 10^-exponent fits into a double.
- *result = static_cast<double>(ReadUint64(trimmed));
+ *result = static_cast<double>(ReadUint64(trimmed, &read_digits));
+ ASSERT(read_digits == trimmed.length());
*result /= exact_powers_of_ten[-exponent];
return true;
}
if (0 <= exponent && exponent < kExactPowersOfTenSize) {
// 10^exponent fits into a double.
- *result = static_cast<double>(ReadUint64(trimmed));
+ *result = static_cast<double>(ReadUint64(trimmed, &read_digits));
+ ASSERT(read_digits == trimmed.length());
*result *= exact_powers_of_ten[exponent];
return true;
}
@@ -187,7 +227,8 @@
// The trimmed string was short and we can multiply it with
// 10^remaining_digits. As a result the remaining exponent now fits
// into a double too.
- *result = static_cast<double>(ReadUint64(trimmed));
+ *result = static_cast<double>(ReadUint64(trimmed, &read_digits));
+ ASSERT(read_digits == trimmed.length());
*result *= exact_powers_of_ten[remaining_digits];
*result *= exact_powers_of_ten[exponent - remaining_digits];
return true;
@@ -197,6 +238,142 @@
}
+// Returns 10^exponent as an exact DiyFp.
+// The given exponent must be in the range [1; kDecimalExponentDistance[.
+static DiyFp AdjustmentPowerOfTen(int exponent) {
+ ASSERT(0 < exponent);
+ ASSERT(exponent < PowersOfTenCache::kDecimalExponentDistance);
+ // Simply hardcode the remaining powers for the given decimal exponent
+ // distance.
+ ASSERT(PowersOfTenCache::kDecimalExponentDistance == 8);
+ switch (exponent) {
+ case 1: return DiyFp(V8_2PART_UINT64_C(0xa0000000, 00000000), -60);
+ case 2: return DiyFp(V8_2PART_UINT64_C(0xc8000000, 00000000), -57);
+ case 3: return DiyFp(V8_2PART_UINT64_C(0xfa000000, 00000000), -54);
+ case 4: return DiyFp(V8_2PART_UINT64_C(0x9c400000, 00000000), -50);
+ case 5: return DiyFp(V8_2PART_UINT64_C(0xc3500000, 00000000), -47);
+ case 6: return DiyFp(V8_2PART_UINT64_C(0xf4240000, 00000000), -44);
+ case 7: return DiyFp(V8_2PART_UINT64_C(0x98968000, 00000000), -40);
+ default:
+ UNREACHABLE();
+ return DiyFp(0, 0);
+ }
+}
+
+
+// If the function returns true then the result is the correct double.
+// Otherwise it is either the correct double or the double that is just below
+// the correct double.
+static bool DiyFpStrtod(Vector<const char> buffer,
+ int exponent,
+ double* result) {
+ DiyFp input;
+ int remaining_decimals;
+ ReadDiyFp(buffer, &input, &remaining_decimals);
+ // Since we may have dropped some digits the input is not accurate.
+ // If remaining_decimals is different than 0 than the error is at most
+ // .5 ulp (unit in the last place).
+ // We don't want to deal with fractions and therefore keep a common
+ // denominator.
+ const int kDenominatorLog = 3;
+ const int kDenominator = 1 << kDenominatorLog;
+ // Move the remaining decimals into the exponent.
+ exponent += remaining_decimals;
+ int error = (remaining_decimals == 0 ? 0 : kDenominator / 2);
+
+ int old_e = input.e();
+ input.Normalize();
+ error <<= old_e - input.e();
+
+ ASSERT(exponent <= PowersOfTenCache::kMaxDecimalExponent);
+ if (exponent < PowersOfTenCache::kMinDecimalExponent) {
+ *result = 0.0;
+ return true;
+ }
+ DiyFp cached_power;
+ int cached_decimal_exponent;
+ PowersOfTenCache::GetCachedPowerForDecimalExponent(exponent,
+ &cached_power,
+ &cached_decimal_exponent);
+
+ if (cached_decimal_exponent != exponent) {
+ int adjustment_exponent = exponent - cached_decimal_exponent;
+ DiyFp adjustment_power = AdjustmentPowerOfTen(adjustment_exponent);
+ input.Multiply(adjustment_power);
+ if (kMaxUint64DecimalDigits - buffer.length() >= adjustment_exponent) {
+ // The product of input with the adjustment power fits into a 64 bit
+ // integer.
+ ASSERT(DiyFp::kSignificandSize == 64);
+ } else {
+ // The adjustment power is exact. There is hence only an error of 0.5.
+ error += kDenominator / 2;
+ }
+ }
+
+ input.Multiply(cached_power);
+ // The error introduced by a multiplication of a*b equals
+ // error_a + error_b + error_a*error_b/2^64 + 0.5
+ // Substituting a with 'input' and b with 'cached_power' we have
+ // error_b = 0.5 (all cached powers have an error of less than 0.5 ulp),
+ // error_ab = 0 or 1 / kDenominator > error_a*error_b/ 2^64
+ int error_b = kDenominator / 2;
+ int error_ab = (error == 0 ? 0 : 1); // We round up to 1.
+ int fixed_error = kDenominator / 2;
+ error += error_b + error_ab + fixed_error;
+
+ old_e = input.e();
+ input.Normalize();
+ error <<= old_e - input.e();
+
+ // See if the double's significand changes if we add/subtract the error.
+ int order_of_magnitude = DiyFp::kSignificandSize + input.e();
+ int effective_significand_size =
+ Double::SignificandSizeForOrderOfMagnitude(order_of_magnitude);
+ int precision_digits_count =
+ DiyFp::kSignificandSize - effective_significand_size;
+ if (precision_digits_count + kDenominatorLog >= DiyFp::kSignificandSize) {
+ // This can only happen for very small denormals. In this case the
+ // half-way multiplied by the denominator exceeds the range of an uint64.
+ // Simply shift everything to the right.
+ int shift_amount = (precision_digits_count + kDenominatorLog) -
+ DiyFp::kSignificandSize + 1;
+ input.set_f(input.f() >> shift_amount);
+ input.set_e(input.e() + shift_amount);
+ // We add 1 for the lost precision of error, and kDenominator for
+ // the lost precision of input.f().
+ error = (error >> shift_amount) + 1 + kDenominator;
+ precision_digits_count -= shift_amount;
+ }
+ // We use uint64_ts now. This only works if the DiyFp uses uint64_ts too.
+ ASSERT(DiyFp::kSignificandSize == 64);
+ ASSERT(precision_digits_count < 64);
+ uint64_t one64 = 1;
+ uint64_t precision_bits_mask = (one64 << precision_digits_count) - 1;
+ uint64_t precision_bits = input.f() & precision_bits_mask;
+ uint64_t half_way = one64 << (precision_digits_count - 1);
+ precision_bits *= kDenominator;
+ half_way *= kDenominator;
+ DiyFp rounded_input(input.f() >> precision_digits_count,
+ input.e() + precision_digits_count);
+ if (precision_bits >= half_way + error) {
+ rounded_input.set_f(rounded_input.f() + 1);
+ }
+ // If the last_bits are too close to the half-way case than we are too
+ // inaccurate and round down. In this case we return false so that we can
+ // fall back to a more precise algorithm.
+
+ *result = Double(rounded_input).value();
+ if (half_way - error < precision_bits && precision_bits < half_way + error) {
+ // Too imprecise. The caller will have to fall back to a slower version.
+ // However the returned number is guaranteed to be either the correct
+ // double, or the next-lower double.
+ return false;
+ } else {
+ return true;
+ }
+}
+
+
double Strtod(Vector<const char> buffer, int exponent) {
Vector<const char> left_trimmed = TrimLeadingZeros(buffer);
Vector<const char> trimmed = TrimTrailingZeros(left_trimmed);
@@ -204,8 +381,10 @@
if (trimmed.length() == 0) return 0.0;
if (exponent + trimmed.length() - 1 >= kMaxDecimalPower) return V8_INFINITY;
if (exponent + trimmed.length() <= kMinDecimalPower) return 0.0;
+
double result;
- if (DoubleStrtod(trimmed, exponent, &result)) {
+ if (DoubleStrtod(trimmed, exponent, &result) ||
+ DiyFpStrtod(trimmed, exponent, &result)) {
return result;
}
return old_strtod(trimmed, exponent);