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Implement fast case for strtod.

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If there are few non-zero digits and the 10^exponent fits into a double then
we can compute the result using 1 (or 2) double operations.

BUG=
TEST=

Review URL: http://codereview.chromium.org/3584015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5603 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
floitschV8@gmail.com 2010-10-07 12:01:25 +00:00
parent d4afed6bff
commit ce666fc2fe
5 changed files with 257 additions and 4 deletions
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4
src/conversions.cc
View File

@ -354,7 +354,7 @@ static double InternalStringToInt(Iterator current, EndMark end, int radix) {
ASSERT(buffer_pos < kBufferSize);
buffer[buffer_pos] = '\0';
Vector<char> buffer_vector(buffer, buffer_pos);
return sign ? -strtod(buffer_vector, NULL) : strtod(buffer_vector, NULL);
return sign ? -Strtod(buffer_vector, 0) : Strtod(buffer_vector, 0);
}
// The following code causes accumulating rounding error for numbers greater
@ -653,7 +653,7 @@ static double InternalStringToDouble(Iterator current,
ASSERT(buffer_pos < kBufferSize);
buffer[buffer_pos] = '\0';
double converted = strtod(Vector<char>(buffer, buffer_pos), exponent);
double converted = Strtod(Vector<char>(buffer, buffer_pos), exponent);
return sign? -converted: converted;
}

99
src/strtod.cc
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@ -36,9 +36,47 @@
namespace v8 {
namespace internal {
// 2^53 = 9007199254740992.
// 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.
static const int kMaxUint64DecimalDigits = 19;
static const double exact_powers_of_ten[] = {
1.0, // 10^0
10.0,
100.0,
1000.0,
10000.0,
100000.0,
1000000.0,
10000000.0,
100000000.0,
1000000000.0,
10000000000.0, // 10^10
100000000000.0,
1000000000000.0,
10000000000000.0,
100000000000000.0,
1000000000000000.0,
10000000000000000.0,
100000000000000000.0,
1000000000000000000.0,
10000000000000000000.0,
100000000000000000000.0, // 10^20
1000000000000000000000.0,
// 10^22 = 0x21e19e0c9bab2400000 = 0x878678326eac9 * 2^22
10000000000000000000000.0
};
static const int kExactPowersOfTenSize = ARRAY_SIZE(exact_powers_of_ten);
extern "C" double gay_strtod(const char* s00, const char** se);
double strtod(Vector<char> buffer, int exponent) {
static double old_strtod(Vector<char> buffer, int exponent) {
char gay_buffer[1024];
Vector<char> gay_buffer_vector(gay_buffer, sizeof(gay_buffer));
buffer.start()[buffer.length()] = '\0';
@ -46,4 +84,63 @@ double strtod(Vector<char> buffer, int exponent) {
return gay_strtod(gay_buffer, NULL);
}
static Vector<char> TrimTrailingZeros(Vector<char> buffer) {
for (int i = buffer.length() - 1; i >= 0; --i) {
if (buffer[i] != '0') {
return Vector<char>(buffer.start(), i + 1);
}
}
return Vector<char>(buffer.start(), 0);
}
uint64_t ReadUint64(Vector<char> buffer) {
ASSERT(buffer.length() <= kMaxUint64DecimalDigits);
uint64_t result = 0;
for (int i = 0; i < buffer.length(); ++i) {
int digit = buffer[i] - '0';
ASSERT(0 <= digit && digit <= 9);
result = 10 * result + digit;
}
return result;
}
double Strtod(Vector<char> buffer, int exponent) {
Vector<char> trimmed = TrimTrailingZeros(buffer);
if (trimmed.length() == 0) return 0.0;
exponent += buffer.length() - trimmed.length();
if (trimmed.length() <= kMaxExactDoubleIntegerDecimalDigits) {
// 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
// two numbers.
// This is possible because IEEE guarantees that floating-point operations
// return the best possible approximation.
if (exponent < 0 && -exponent < kExactPowersOfTenSize) {
// 10^-exponent fits into a double.
double buffer_d = static_cast<double>(ReadUint64(trimmed));
return buffer_d / exact_powers_of_ten[-exponent];
}
if (0 <= exponent && exponent < kExactPowersOfTenSize) {
// 10^exponent fits into a double.
double buffer_d = static_cast<double>(ReadUint64(trimmed));
return buffer_d * exact_powers_of_ten[exponent];
}
int remaining_digits =
kMaxExactDoubleIntegerDecimalDigits - trimmed.length();
if ((0 <= exponent) &&
(exponent - remaining_digits < kExactPowersOfTenSize)) {
// 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.
double buffer_d = static_cast<double>(ReadUint64(trimmed));
buffer_d *= exact_powers_of_ten[remaining_digits];
return buffer_d * exact_powers_of_ten[exponent - remaining_digits];
}
}
return old_strtod(trimmed, exponent);
}
} } // namespace v8::internal

2
src/strtod.h
View File

@ -33,7 +33,7 @@ namespace internal {
// The buffer must only contain digits in the range [0-9]. It must not
// contain a dot or a sign. It must not start with '0', and must not be empty.
double strtod(Vector<char> buffer, int exponent);
double Strtod(Vector<char> buffer, int exponent);
} } // namespace v8::internal

1
test/cctest/SConscript
View File

@ -70,6 +70,7 @@ SOURCES = {
'test-sockets.cc',
'test-spaces.cc',
'test-strings.cc',
'test-strtod.cc',
'test-thread-termination.cc',
'test-threads.cc',
'test-type-info.cc',

155
test/cctest/test-strtod.cc Normal file
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@ -0,0 +1,155 @@
// Copyright 2006-2008 the V8 project authors. All rights reserved.
#include <stdlib.h>
#include "v8.h"
#include "platform.h"
#include "cctest.h"
#include "strtod.h"
using namespace v8::internal;
static const int kBufferSize = 100;
TEST(Strtod) {
char buffer[kBufferSize];
Vector<char> vector;
strncpy(buffer, "0", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(0.0, Strtod(vector, 1));
CHECK_EQ(0.0, Strtod(vector, 2));
CHECK_EQ(0.0, Strtod(vector, -2));
CHECK_EQ(0.0, Strtod(vector, -999));
CHECK_EQ(0.0, Strtod(vector, +999));
strncpy(buffer, "1", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(1.0, Strtod(vector, 0));
CHECK_EQ(10.0, Strtod(vector, 1));
CHECK_EQ(100.0, Strtod(vector, 2));
CHECK_EQ(1e20, Strtod(vector, 20));
CHECK_EQ(1e22, Strtod(vector, 22));
CHECK_EQ(1e23, Strtod(vector, 23));
CHECK_EQ(1e35, Strtod(vector, 35));
CHECK_EQ(1e36, Strtod(vector, 36));
CHECK_EQ(1e37, Strtod(vector, 37));
CHECK_EQ(1e-1, Strtod(vector, -1));
CHECK_EQ(1e-2, Strtod(vector, -2));
CHECK_EQ(1e-5, Strtod(vector, -5));
CHECK_EQ(1e-20, Strtod(vector, -20));
CHECK_EQ(1e-22, Strtod(vector, -22));
CHECK_EQ(1e-23, Strtod(vector, -23));
CHECK_EQ(1e-25, Strtod(vector, -25));
CHECK_EQ(1e-39, Strtod(vector, -39));
strncpy(buffer, "2", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(2.0, Strtod(vector, 0));
CHECK_EQ(20.0, Strtod(vector, 1));
CHECK_EQ(200.0, Strtod(vector, 2));
CHECK_EQ(2e20, Strtod(vector, 20));
CHECK_EQ(2e22, Strtod(vector, 22));
CHECK_EQ(2e23, Strtod(vector, 23));
CHECK_EQ(2e35, Strtod(vector, 35));
CHECK_EQ(2e36, Strtod(vector, 36));
CHECK_EQ(2e37, Strtod(vector, 37));
CHECK_EQ(2e-1, Strtod(vector, -1));
CHECK_EQ(2e-2, Strtod(vector, -2));
CHECK_EQ(2e-5, Strtod(vector, -5));
CHECK_EQ(2e-20, Strtod(vector, -20));
CHECK_EQ(2e-22, Strtod(vector, -22));
CHECK_EQ(2e-23, Strtod(vector, -23));
CHECK_EQ(2e-25, Strtod(vector, -25));
CHECK_EQ(2e-39, Strtod(vector, -39));
strncpy(buffer, "9", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(9.0, Strtod(vector, 0));
CHECK_EQ(90.0, Strtod(vector, 1));
CHECK_EQ(900.0, Strtod(vector, 2));
CHECK_EQ(9e20, Strtod(vector, 20));
CHECK_EQ(9e22, Strtod(vector, 22));
CHECK_EQ(9e23, Strtod(vector, 23));
CHECK_EQ(9e35, Strtod(vector, 35));
CHECK_EQ(9e36, Strtod(vector, 36));
CHECK_EQ(9e37, Strtod(vector, 37));
CHECK_EQ(9e-1, Strtod(vector, -1));
CHECK_EQ(9e-2, Strtod(vector, -2));
CHECK_EQ(9e-5, Strtod(vector, -5));
CHECK_EQ(9e-20, Strtod(vector, -20));
CHECK_EQ(9e-22, Strtod(vector, -22));
CHECK_EQ(9e-23, Strtod(vector, -23));
CHECK_EQ(9e-25, Strtod(vector, -25));
CHECK_EQ(9e-39, Strtod(vector, -39));
strncpy(buffer, "12345", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(12345.0, Strtod(vector, 0));
CHECK_EQ(123450.0, Strtod(vector, 1));
CHECK_EQ(1234500.0, Strtod(vector, 2));
CHECK_EQ(12345e20, Strtod(vector, 20));
CHECK_EQ(12345e22, Strtod(vector, 22));
CHECK_EQ(12345e23, Strtod(vector, 23));
CHECK_EQ(12345e30, Strtod(vector, 30));
CHECK_EQ(12345e31, Strtod(vector, 31));
CHECK_EQ(12345e32, Strtod(vector, 32));
CHECK_EQ(12345e35, Strtod(vector, 35));
CHECK_EQ(12345e36, Strtod(vector, 36));
CHECK_EQ(12345e37, Strtod(vector, 37));
CHECK_EQ(12345e-1, Strtod(vector, -1));
CHECK_EQ(12345e-2, Strtod(vector, -2));
CHECK_EQ(12345e-5, Strtod(vector, -5));
CHECK_EQ(12345e-20, Strtod(vector, -20));
CHECK_EQ(12345e-22, Strtod(vector, -22));
CHECK_EQ(12345e-23, Strtod(vector, -23));
CHECK_EQ(12345e-25, Strtod(vector, -25));
CHECK_EQ(12345e-39, Strtod(vector, -39));
strncpy(buffer, "12345678901234", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(12345678901234.0, Strtod(vector, 0));
CHECK_EQ(123456789012340.0, Strtod(vector, 1));
CHECK_EQ(1234567890123400.0, Strtod(vector, 2));
CHECK_EQ(12345678901234e20, Strtod(vector, 20));
CHECK_EQ(12345678901234e22, Strtod(vector, 22));
CHECK_EQ(12345678901234e23, Strtod(vector, 23));
CHECK_EQ(12345678901234e30, Strtod(vector, 30));
CHECK_EQ(12345678901234e31, Strtod(vector, 31));
CHECK_EQ(12345678901234e32, Strtod(vector, 32));
CHECK_EQ(12345678901234e35, Strtod(vector, 35));
CHECK_EQ(12345678901234e36, Strtod(vector, 36));
CHECK_EQ(12345678901234e37, Strtod(vector, 37));
CHECK_EQ(12345678901234e-1, Strtod(vector, -1));
CHECK_EQ(12345678901234e-2, Strtod(vector, -2));
CHECK_EQ(12345678901234e-5, Strtod(vector, -5));
CHECK_EQ(12345678901234e-20, Strtod(vector, -20));
CHECK_EQ(12345678901234e-22, Strtod(vector, -22));
CHECK_EQ(12345678901234e-23, Strtod(vector, -23));
CHECK_EQ(12345678901234e-25, Strtod(vector, -25));
CHECK_EQ(12345678901234e-39, Strtod(vector, -39));
strncpy(buffer, "123456789012345", kBufferSize);
vector = Vector<char>(buffer, strlen(buffer));
CHECK_EQ(123456789012345.0, Strtod(vector, 0));
CHECK_EQ(1234567890123450.0, Strtod(vector, 1));
CHECK_EQ(12345678901234500.0, Strtod(vector, 2));
CHECK_EQ(123456789012345e20, Strtod(vector, 20));
CHECK_EQ(123456789012345e22, Strtod(vector, 22));
CHECK_EQ(123456789012345e23, Strtod(vector, 23));
CHECK_EQ(123456789012345e35, Strtod(vector, 35));
CHECK_EQ(123456789012345e36, Strtod(vector, 36));
CHECK_EQ(123456789012345e37, Strtod(vector, 37));
CHECK_EQ(123456789012345e39, Strtod(vector, 39));
CHECK_EQ(123456789012345e-1, Strtod(vector, -1));
CHECK_EQ(123456789012345e-2, Strtod(vector, -2));
CHECK_EQ(123456789012345e-5, Strtod(vector, -5));
CHECK_EQ(123456789012345e-20, Strtod(vector, -20));
CHECK_EQ(123456789012345e-22, Strtod(vector, -22));
CHECK_EQ(123456789012345e-23, Strtod(vector, -23));
CHECK_EQ(123456789012345e-25, Strtod(vector, -25));
CHECK_EQ(123456789012345e-39, Strtod(vector, -39));
}