1 // Copyright 2011 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_DTOA_H_ 6 #define V8_DTOA_H_ 7 8 namespace v8 { 9 namespace internal { 10 11 enum DtoaMode { 12 // Return the shortest correct representation. 13 // For example the output of 0.299999999999999988897 is (the less accurate but 14 // correct) 0.3. 15 DTOA_SHORTEST, 16 // Return a fixed number of digits after the decimal point. 17 // For instance fixed(0.1, 4) becomes 0.1000 18 // If the input number is big, the output will be big. 19 DTOA_FIXED, 20 // Return a fixed number of digits, no matter what the exponent is. 21 DTOA_PRECISION 22 }; 23 24 // The maximal length of digits a double can have in base 10. 25 // Note that DoubleToAscii null-terminates its input. So the given buffer should 26 // be at least kBase10MaximalLength + 1 characters long. 27 const int kBase10MaximalLength = 17; 28 29 // Converts the given double 'v' to ASCII. 30 // The result should be interpreted as buffer * 10^(point-length). 31 // 32 // The output depends on the given mode: 33 // - SHORTEST: produce the least amount of digits for which the internal 34 // identity requirement is still satisfied. If the digits are printed 35 // (together with the correct exponent) then reading this number will give 36 // 'v' again. The buffer will choose the representation that is closest to 37 // 'v'. If there are two at the same distance, than the one farther away 38 // from 0 is chosen (halfway cases - ending with 5 - are rounded up). 39 // In this mode the 'requested_digits' parameter is ignored. 40 // - FIXED: produces digits necessary to print a given number with 41 // 'requested_digits' digits after the decimal point. The produced digits 42 // might be too short in which case the caller has to fill the gaps with '0's. 43 // Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2. 44 // Halfway cases are rounded towards +/-Infinity (away from 0). The call 45 // toFixed(0.15, 2) thus returns buffer="2", point=0. 46 // The returned buffer may contain digits that would be truncated from the 47 // shortest representation of the input. 48 // - PRECISION: produces 'requested_digits' where the first digit is not '0'. 49 // Even though the length of produced digits usually equals 50 // 'requested_digits', the function is allowed to return fewer digits, in 51 // which case the caller has to fill the missing digits with '0's. 52 // Halfway cases are again rounded away from 0. 53 // 'DoubleToAscii' expects the given buffer to be big enough to hold all digits 54 // and a terminating null-character. In SHORTEST-mode it expects a buffer of 55 // at least kBase10MaximalLength + 1. Otherwise, the size of the output is 56 // limited to requested_digits digits plus the null terminator. 57 void DoubleToAscii(double v, DtoaMode mode, int requested_digits, 58 Vector<char> buffer, int* sign, int* length, int* point); 59 60 } } // namespace v8::internal 61 62 #endif // V8_DTOA_H_ 63
