v8/src/fixed-dtoa.cc
Clemens Hammacher 5f6510825a [cleanup] Fix remaining (D)CHECK macro usages
This CL fixes all occurences that don't require special OWNER reviews,
or can be reviewed by Michi.

After this one, we should be able to reenable the readability/check
cpplint check.

R=mstarzinger@chromium.org

Bug: v8:6837, v8:6921
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng;master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: Ic81d68d5534eaa795b7197fed5c41ed158361d62
Reviewed-on: https://chromium-review.googlesource.com/721120
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48670}
2017-10-18 10:12:31 +00:00

386 lines
13 KiB
C++

// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <stdint.h>
#include <cmath>
#include "src/base/logging.h"
#include "src/utils.h"
#include "src/double.h"
#include "src/fixed-dtoa.h"
namespace v8 {
namespace internal {
// Represents a 128bit type. This class should be replaced by a native type on
// platforms that support 128bit integers.
class UInt128 {
public:
UInt128() : high_bits_(0), low_bits_(0) { }
UInt128(uint64_t high, uint64_t low) : high_bits_(high), low_bits_(low) { }
void Multiply(uint32_t multiplicand) {
uint64_t accumulator;
accumulator = (low_bits_ & kMask32) * multiplicand;
uint32_t part = static_cast<uint32_t>(accumulator & kMask32);
accumulator >>= 32;
accumulator = accumulator + (low_bits_ >> 32) * multiplicand;
low_bits_ = (accumulator << 32) + part;
accumulator >>= 32;
accumulator = accumulator + (high_bits_ & kMask32) * multiplicand;
part = static_cast<uint32_t>(accumulator & kMask32);
accumulator >>= 32;
accumulator = accumulator + (high_bits_ >> 32) * multiplicand;
high_bits_ = (accumulator << 32) + part;
DCHECK_EQ(accumulator >> 32, 0);
}
void Shift(int shift_amount) {
DCHECK(-64 <= shift_amount && shift_amount <= 64);
if (shift_amount == 0) {
return;
} else if (shift_amount == -64) {
high_bits_ = low_bits_;
low_bits_ = 0;
} else if (shift_amount == 64) {
low_bits_ = high_bits_;
high_bits_ = 0;
} else if (shift_amount <= 0) {
high_bits_ <<= -shift_amount;
high_bits_ += low_bits_ >> (64 + shift_amount);
low_bits_ <<= -shift_amount;
} else {
low_bits_ >>= shift_amount;
low_bits_ += high_bits_ << (64 - shift_amount);
high_bits_ >>= shift_amount;
}
}
// Modifies *this to *this MOD (2^power).
// Returns *this DIV (2^power).
int DivModPowerOf2(int power) {
if (power >= 64) {
int result = static_cast<int>(high_bits_ >> (power - 64));
high_bits_ -= static_cast<uint64_t>(result) << (power - 64);
return result;
} else {
uint64_t part_low = low_bits_ >> power;
uint64_t part_high = high_bits_ << (64 - power);
int result = static_cast<int>(part_low + part_high);
high_bits_ = 0;
low_bits_ -= part_low << power;
return result;
}
}
bool IsZero() const {
return high_bits_ == 0 && low_bits_ == 0;
}
int BitAt(int position) {
if (position >= 64) {
return static_cast<int>(high_bits_ >> (position - 64)) & 1;
} else {
return static_cast<int>(low_bits_ >> position) & 1;
}
}
private:
static const uint64_t kMask32 = 0xFFFFFFFF;
// Value == (high_bits_ << 64) + low_bits_
uint64_t high_bits_;
uint64_t low_bits_;
};
static const int kDoubleSignificandSize = 53; // Includes the hidden bit.
static void FillDigits32FixedLength(uint32_t number, int requested_length,
Vector<char> buffer, int* length) {
for (int i = requested_length - 1; i >= 0; --i) {
buffer[(*length) + i] = '0' + number % 10;
number /= 10;
}
*length += requested_length;
}
static void FillDigits32(uint32_t number, Vector<char> buffer, int* length) {
int number_length = 0;
// We fill the digits in reverse order and exchange them afterwards.
while (number != 0) {
int digit = number % 10;
number /= 10;
buffer[(*length) + number_length] = '0' + digit;
number_length++;
}
// Exchange the digits.
int i = *length;
int j = *length + number_length - 1;
while (i < j) {
char tmp = buffer[i];
buffer[i] = buffer[j];
buffer[j] = tmp;
i++;
j--;
}
*length += number_length;
}
static void FillDigits64FixedLength(uint64_t number, int requested_length,
Vector<char> buffer, int* length) {
const uint32_t kTen7 = 10000000;
// For efficiency cut the number into 3 uint32_t parts, and print those.
uint32_t part2 = static_cast<uint32_t>(number % kTen7);
number /= kTen7;
uint32_t part1 = static_cast<uint32_t>(number % kTen7);
uint32_t part0 = static_cast<uint32_t>(number / kTen7);
FillDigits32FixedLength(part0, 3, buffer, length);
FillDigits32FixedLength(part1, 7, buffer, length);
FillDigits32FixedLength(part2, 7, buffer, length);
}
static void FillDigits64(uint64_t number, Vector<char> buffer, int* length) {
const uint32_t kTen7 = 10000000;
// For efficiency cut the number into 3 uint32_t parts, and print those.
uint32_t part2 = static_cast<uint32_t>(number % kTen7);
number /= kTen7;
uint32_t part1 = static_cast<uint32_t>(number % kTen7);
uint32_t part0 = static_cast<uint32_t>(number / kTen7);
if (part0 != 0) {
FillDigits32(part0, buffer, length);
FillDigits32FixedLength(part1, 7, buffer, length);
FillDigits32FixedLength(part2, 7, buffer, length);
} else if (part1 != 0) {
FillDigits32(part1, buffer, length);
FillDigits32FixedLength(part2, 7, buffer, length);
} else {
FillDigits32(part2, buffer, length);
}
}
static void DtoaRoundUp(Vector<char> buffer, int* length, int* decimal_point) {
// An empty buffer represents 0.
if (*length == 0) {
buffer[0] = '1';
*decimal_point = 1;
*length = 1;
return;
}
// Round the last digit until we either have a digit that was not '9' or until
// we reached the first digit.
buffer[(*length) - 1]++;
for (int i = (*length) - 1; i > 0; --i) {
if (buffer[i] != '0' + 10) {
return;
}
buffer[i] = '0';
buffer[i - 1]++;
}
// If the first digit is now '0' + 10, we would need to set it to '0' and add
// a '1' in front. However we reach the first digit only if all following
// digits had been '9' before rounding up. Now all trailing digits are '0' and
// we simply switch the first digit to '1' and update the decimal-point
// (indicating that the point is now one digit to the right).
if (buffer[0] == '0' + 10) {
buffer[0] = '1';
(*decimal_point)++;
}
}
// The given fractionals number represents a fixed-point number with binary
// point at bit (-exponent).
// Preconditions:
// -128 <= exponent <= 0.
// 0 <= fractionals * 2^exponent < 1
// The buffer holds the result.
// The function will round its result. During the rounding-process digits not
// generated by this function might be updated, and the decimal-point variable
// might be updated. If this function generates the digits 99 and the buffer
// already contained "199" (thus yielding a buffer of "19999") then a
// rounding-up will change the contents of the buffer to "20000".
static void FillFractionals(uint64_t fractionals, int exponent,
int fractional_count, Vector<char> buffer,
int* length, int* decimal_point) {
DCHECK(-128 <= exponent && exponent <= 0);
// 'fractionals' is a fixed-point number, with binary point at bit
// (-exponent). Inside the function the non-converted remainder of fractionals
// is a fixed-point number, with binary point at bit 'point'.
if (-exponent <= 64) {
// One 64 bit number is sufficient.
DCHECK_EQ(fractionals >> 56, 0);
int point = -exponent;
for (int i = 0; i < fractional_count; ++i) {
if (fractionals == 0) break;
// Instead of multiplying by 10 we multiply by 5 and adjust the point
// location. This way the fractionals variable will not overflow.
// Invariant at the beginning of the loop: fractionals < 2^point.
// Initially we have: point <= 64 and fractionals < 2^56
// After each iteration the point is decremented by one.
// Note that 5^3 = 125 < 128 = 2^7.
// Therefore three iterations of this loop will not overflow fractionals
// (even without the subtraction at the end of the loop body). At this
// time point will satisfy point <= 61 and therefore fractionals < 2^point
// and any further multiplication of fractionals by 5 will not overflow.
fractionals *= 5;
point--;
int digit = static_cast<int>(fractionals >> point);
buffer[*length] = '0' + digit;
(*length)++;
fractionals -= static_cast<uint64_t>(digit) << point;
}
// If the first bit after the point is set we have to round up.
if (((fractionals >> (point - 1)) & 1) == 1) {
DtoaRoundUp(buffer, length, decimal_point);
}
} else { // We need 128 bits.
DCHECK(64 < -exponent && -exponent <= 128);
UInt128 fractionals128 = UInt128(fractionals, 0);
fractionals128.Shift(-exponent - 64);
int point = 128;
for (int i = 0; i < fractional_count; ++i) {
if (fractionals128.IsZero()) break;
// As before: instead of multiplying by 10 we multiply by 5 and adjust the
// point location.
// This multiplication will not overflow for the same reasons as before.
fractionals128.Multiply(5);
point--;
int digit = fractionals128.DivModPowerOf2(point);
buffer[*length] = '0' + digit;
(*length)++;
}
if (fractionals128.BitAt(point - 1) == 1) {
DtoaRoundUp(buffer, length, decimal_point);
}
}
}
// Removes leading and trailing zeros.
// If leading zeros are removed then the decimal point position is adjusted.
static void TrimZeros(Vector<char> buffer, int* length, int* decimal_point) {
while (*length > 0 && buffer[(*length) - 1] == '0') {
(*length)--;
}
int first_non_zero = 0;
while (first_non_zero < *length && buffer[first_non_zero] == '0') {
first_non_zero++;
}
if (first_non_zero != 0) {
for (int i = first_non_zero; i < *length; ++i) {
buffer[i - first_non_zero] = buffer[i];
}
*length -= first_non_zero;
*decimal_point -= first_non_zero;
}
}
bool FastFixedDtoa(double v,
int fractional_count,
Vector<char> buffer,
int* length,
int* decimal_point) {
const uint32_t kMaxUInt32 = 0xFFFFFFFF;
uint64_t significand = Double(v).Significand();
int exponent = Double(v).Exponent();
// v = significand * 2^exponent (with significand a 53bit integer).
// If the exponent is larger than 20 (i.e. we may have a 73bit number) then we
// don't know how to compute the representation. 2^73 ~= 9.5*10^21.
// If necessary this limit could probably be increased, but we don't need
// more.
if (exponent > 20) return false;
if (fractional_count > 20) return false;
*length = 0;
// At most kDoubleSignificandSize bits of the significand are non-zero.
// Given a 64 bit integer we have 11 0s followed by 53 potentially non-zero
// bits: 0..11*..0xxx..53*..xx
if (exponent + kDoubleSignificandSize > 64) {
// The exponent must be > 11.
//
// We know that v = significand * 2^exponent.
// And the exponent > 11.
// We simplify the task by dividing v by 10^17.
// The quotient delivers the first digits, and the remainder fits into a 64
// bit number.
// Dividing by 10^17 is equivalent to dividing by 5^17*2^17.
const uint64_t kFive17 = V8_2PART_UINT64_C(0xB1, A2BC2EC5); // 5^17
uint64_t divisor = kFive17;
int divisor_power = 17;
uint64_t dividend = significand;
uint32_t quotient;
uint64_t remainder;
// Let v = f * 2^e with f == significand and e == exponent.
// Then need q (quotient) and r (remainder) as follows:
// v = q * 10^17 + r
// f * 2^e = q * 10^17 + r
// f * 2^e = q * 5^17 * 2^17 + r
// If e > 17 then
// f * 2^(e-17) = q * 5^17 + r/2^17
// else
// f = q * 5^17 * 2^(17-e) + r/2^e
if (exponent > divisor_power) {
// We only allow exponents of up to 20 and therefore (17 - e) <= 3
dividend <<= exponent - divisor_power;
quotient = static_cast<uint32_t>(dividend / divisor);
remainder = (dividend % divisor) << divisor_power;
} else {
divisor <<= divisor_power - exponent;
quotient = static_cast<uint32_t>(dividend / divisor);
remainder = (dividend % divisor) << exponent;
}
FillDigits32(quotient, buffer, length);
FillDigits64FixedLength(remainder, divisor_power, buffer, length);
*decimal_point = *length;
} else if (exponent >= 0) {
// 0 <= exponent <= 11
significand <<= exponent;
FillDigits64(significand, buffer, length);
*decimal_point = *length;
} else if (exponent > -kDoubleSignificandSize) {
// We have to cut the number.
uint64_t integrals = significand >> -exponent;
uint64_t fractionals = significand - (integrals << -exponent);
if (integrals > kMaxUInt32) {
FillDigits64(integrals, buffer, length);
} else {
FillDigits32(static_cast<uint32_t>(integrals), buffer, length);
}
*decimal_point = *length;
FillFractionals(fractionals, exponent, fractional_count,
buffer, length, decimal_point);
} else if (exponent < -128) {
// This configuration (with at most 20 digits) means that all digits must be
// 0.
DCHECK_LE(fractional_count, 20);
buffer[0] = '\0';
*length = 0;
*decimal_point = -fractional_count;
} else {
*decimal_point = 0;
FillFractionals(significand, exponent, fractional_count,
buffer, length, decimal_point);
}
TrimZeros(buffer, length, decimal_point);
buffer[*length] = '\0';
if ((*length) == 0) {
// The string is empty and the decimal_point thus has no importance. Mimick
// Gay's dtoa and and set it to -fractional_count.
*decimal_point = -fractional_count;
}
return true;
}
} // namespace internal
} // namespace v8