Ben Murdoch | f87a203 | 2010-10-22 12:50:53 +0100 | [diff] [blame^] | 1 | // Copyright 2010 the V8 project authors. All rights reserved. |
| 2 | // Redistribution and use in source and binary forms, with or without |
| 3 | // modification, are permitted provided that the following conditions are |
| 4 | // met: |
| 5 | // |
| 6 | // * Redistributions of source code must retain the above copyright |
| 7 | // notice, this list of conditions and the following disclaimer. |
| 8 | // * Redistributions in binary form must reproduce the above |
| 9 | // copyright notice, this list of conditions and the following |
| 10 | // disclaimer in the documentation and/or other materials provided |
| 11 | // with the distribution. |
| 12 | // * Neither the name of Google Inc. nor the names of its |
| 13 | // contributors may be used to endorse or promote products derived |
| 14 | // from this software without specific prior written permission. |
| 15 | // |
| 16 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 17 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 18 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 19 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 20 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 21 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 22 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 23 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 24 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 25 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 26 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 27 | |
| 28 | #include <stdarg.h> |
| 29 | #include <limits.h> |
| 30 | |
| 31 | #include "v8.h" |
| 32 | |
| 33 | #include "strtod.h" |
| 34 | // #include "cached-powers.h" |
| 35 | |
| 36 | namespace v8 { |
| 37 | namespace internal { |
| 38 | |
| 39 | // 2^53 = 9007199254740992. |
| 40 | // Any integer with at most 15 decimal digits will hence fit into a double |
| 41 | // (which has a 53bit significand) without loss of precision. |
| 42 | static const int kMaxExactDoubleIntegerDecimalDigits = 15; |
| 43 | // 2^64 = 18446744073709551616 |
| 44 | // Any integer with at most 19 digits will hence fit into a 64bit datatype. |
| 45 | static const int kMaxUint64DecimalDigits = 19; |
| 46 | // Max double: 1.7976931348623157 x 10^308 |
| 47 | // Min non-zero double: 4.9406564584124654 x 10^-324 |
| 48 | // Any x >= 10^309 is interpreted as +infinity. |
| 49 | // Any x <= 10^-324 is interpreted as 0. |
| 50 | // Note that 2.5e-324 (despite being smaller than the min double) will be read |
| 51 | // as non-zero (equal to the min non-zero double). |
| 52 | static const int kMaxDecimalPower = 309; |
| 53 | static const int kMinDecimalPower = -324; |
| 54 | |
| 55 | static const double exact_powers_of_ten[] = { |
| 56 | 1.0, // 10^0 |
| 57 | 10.0, |
| 58 | 100.0, |
| 59 | 1000.0, |
| 60 | 10000.0, |
| 61 | 100000.0, |
| 62 | 1000000.0, |
| 63 | 10000000.0, |
| 64 | 100000000.0, |
| 65 | 1000000000.0, |
| 66 | 10000000000.0, // 10^10 |
| 67 | 100000000000.0, |
| 68 | 1000000000000.0, |
| 69 | 10000000000000.0, |
| 70 | 100000000000000.0, |
| 71 | 1000000000000000.0, |
| 72 | 10000000000000000.0, |
| 73 | 100000000000000000.0, |
| 74 | 1000000000000000000.0, |
| 75 | 10000000000000000000.0, |
| 76 | 100000000000000000000.0, // 10^20 |
| 77 | 1000000000000000000000.0, |
| 78 | // 10^22 = 0x21e19e0c9bab2400000 = 0x878678326eac9 * 2^22 |
| 79 | 10000000000000000000000.0 |
| 80 | }; |
| 81 | |
| 82 | static const int kExactPowersOfTenSize = ARRAY_SIZE(exact_powers_of_ten); |
| 83 | |
| 84 | |
| 85 | extern "C" double gay_strtod(const char* s00, const char** se); |
| 86 | |
| 87 | static double old_strtod(Vector<const char> buffer, int exponent) { |
| 88 | // gay_strtod is broken on Linux,x86. For numbers with few decimal digits |
| 89 | // the computation is done using floating-point operations which (on Linux) |
| 90 | // are prone to double-rounding errors. |
| 91 | // By adding several zeroes to the buffer gay_strtod falls back to a slower |
| 92 | // (but correct) algorithm. |
| 93 | const int kInsertedZeroesCount = 20; |
| 94 | char gay_buffer[1024]; |
| 95 | Vector<char> gay_buffer_vector(gay_buffer, sizeof(gay_buffer)); |
| 96 | int pos = 0; |
| 97 | for (int i = 0; i < buffer.length(); ++i) { |
| 98 | gay_buffer_vector[pos++] = buffer[i]; |
| 99 | } |
| 100 | for (int i = 0; i < kInsertedZeroesCount; ++i) { |
| 101 | gay_buffer_vector[pos++] = '0'; |
| 102 | } |
| 103 | exponent -= kInsertedZeroesCount; |
| 104 | gay_buffer_vector[pos++] = 'e'; |
| 105 | if (exponent < 0) { |
| 106 | gay_buffer_vector[pos++] = '-'; |
| 107 | exponent = -exponent; |
| 108 | } |
| 109 | const int kNumberOfExponentDigits = 5; |
| 110 | for (int i = kNumberOfExponentDigits - 1; i >= 0; i--) { |
| 111 | gay_buffer_vector[pos + i] = exponent % 10 + '0'; |
| 112 | exponent /= 10; |
| 113 | } |
| 114 | pos += kNumberOfExponentDigits; |
| 115 | gay_buffer_vector[pos] = '\0'; |
| 116 | return gay_strtod(gay_buffer, NULL); |
| 117 | } |
| 118 | |
| 119 | |
| 120 | static Vector<const char> TrimLeadingZeros(Vector<const char> buffer) { |
| 121 | for (int i = 0; i < buffer.length(); i++) { |
| 122 | if (buffer[i] != '0') { |
| 123 | return Vector<const char>(buffer.start() + i, buffer.length() - i); |
| 124 | } |
| 125 | } |
| 126 | return Vector<const char>(buffer.start(), 0); |
| 127 | } |
| 128 | |
| 129 | |
| 130 | static Vector<const char> TrimTrailingZeros(Vector<const char> buffer) { |
| 131 | for (int i = buffer.length() - 1; i >= 0; --i) { |
| 132 | if (buffer[i] != '0') { |
| 133 | return Vector<const char>(buffer.start(), i + 1); |
| 134 | } |
| 135 | } |
| 136 | return Vector<const char>(buffer.start(), 0); |
| 137 | } |
| 138 | |
| 139 | |
| 140 | uint64_t ReadUint64(Vector<const char> buffer) { |
| 141 | ASSERT(buffer.length() <= kMaxUint64DecimalDigits); |
| 142 | uint64_t result = 0; |
| 143 | for (int i = 0; i < buffer.length(); ++i) { |
| 144 | int digit = buffer[i] - '0'; |
| 145 | ASSERT(0 <= digit && digit <= 9); |
| 146 | result = 10 * result + digit; |
| 147 | } |
| 148 | return result; |
| 149 | } |
| 150 | |
| 151 | |
| 152 | static bool DoubleStrtod(Vector<const char> trimmed, |
| 153 | int exponent, |
| 154 | double* result) { |
| 155 | #if (defined(V8_TARGET_ARCH_IA32) || defined(USE_SIMULATOR)) && !defined(WIN32) |
| 156 | // On x86 the floating-point stack can be 64 or 80 bits wide. If it is |
| 157 | // 80 bits wide (as is the case on Linux) then double-rounding occurs and the |
| 158 | // result is not accurate. |
| 159 | // We know that Windows32 uses 64 bits and is therefore accurate. |
| 160 | // Note that the ARM simulator is compiled for 32bits. It therefore exhibits |
| 161 | // the same problem. |
| 162 | return false; |
| 163 | #endif |
| 164 | if (trimmed.length() <= kMaxExactDoubleIntegerDecimalDigits) { |
| 165 | // The trimmed input fits into a double. |
| 166 | // If the 10^exponent (resp. 10^-exponent) fits into a double too then we |
| 167 | // can compute the result-double simply by multiplying (resp. dividing) the |
| 168 | // two numbers. |
| 169 | // This is possible because IEEE guarantees that floating-point operations |
| 170 | // return the best possible approximation. |
| 171 | if (exponent < 0 && -exponent < kExactPowersOfTenSize) { |
| 172 | // 10^-exponent fits into a double. |
| 173 | *result = static_cast<double>(ReadUint64(trimmed)); |
| 174 | *result /= exact_powers_of_ten[-exponent]; |
| 175 | return true; |
| 176 | } |
| 177 | if (0 <= exponent && exponent < kExactPowersOfTenSize) { |
| 178 | // 10^exponent fits into a double. |
| 179 | *result = static_cast<double>(ReadUint64(trimmed)); |
| 180 | *result *= exact_powers_of_ten[exponent]; |
| 181 | return true; |
| 182 | } |
| 183 | int remaining_digits = |
| 184 | kMaxExactDoubleIntegerDecimalDigits - trimmed.length(); |
| 185 | if ((0 <= exponent) && |
| 186 | (exponent - remaining_digits < kExactPowersOfTenSize)) { |
| 187 | // The trimmed string was short and we can multiply it with |
| 188 | // 10^remaining_digits. As a result the remaining exponent now fits |
| 189 | // into a double too. |
| 190 | *result = static_cast<double>(ReadUint64(trimmed)); |
| 191 | *result *= exact_powers_of_ten[remaining_digits]; |
| 192 | *result *= exact_powers_of_ten[exponent - remaining_digits]; |
| 193 | return true; |
| 194 | } |
| 195 | } |
| 196 | return false; |
| 197 | } |
| 198 | |
| 199 | |
| 200 | double Strtod(Vector<const char> buffer, int exponent) { |
| 201 | Vector<const char> left_trimmed = TrimLeadingZeros(buffer); |
| 202 | Vector<const char> trimmed = TrimTrailingZeros(left_trimmed); |
| 203 | exponent += left_trimmed.length() - trimmed.length(); |
| 204 | if (trimmed.length() == 0) return 0.0; |
| 205 | if (exponent + trimmed.length() - 1 >= kMaxDecimalPower) return V8_INFINITY; |
| 206 | if (exponent + trimmed.length() <= kMinDecimalPower) return 0.0; |
| 207 | double result; |
| 208 | if (DoubleStrtod(trimmed, exponent, &result)) { |
| 209 | return result; |
| 210 | } |
| 211 | return old_strtod(trimmed, exponent); |
| 212 | } |
| 213 | |
| 214 | } } // namespace v8::internal |