diff options
Diffstat (limited to 'third_party/skia_shared')
| -rw-r--r-- | third_party/skia_shared/SkFloatToDecimal.cpp | 174 | ||||
| -rw-r--r-- | third_party/skia_shared/SkFloatToDecimal.h | 34 |
2 files changed, 208 insertions, 0 deletions
diff --git a/third_party/skia_shared/SkFloatToDecimal.cpp b/third_party/skia_shared/SkFloatToDecimal.cpp new file mode 100644 index 0000000000..ac24a11e91 --- /dev/null +++ b/third_party/skia_shared/SkFloatToDecimal.cpp @@ -0,0 +1,174 @@ +/* + * Copyright 2017 Google Inc. + * + * Use of this source code is governed by a BSD-style license that can be + * found in the LICENSE file. + */ + +#include "SkFloatToDecimal.h" + +#include <cfloat> +#include <climits> +#include <cmath> + +//#include "SkTypes.h" +#include <cassert> +#define SkASSERT assert + +// Return pow(10.0, e), optimized for common cases. +static double pow10(int e) { + switch (e) { + case 0: return 1.0; // common cases + case 1: return 10.0; + case 2: return 100.0; + case 3: return 1e+03; + case 4: return 1e+04; + case 5: return 1e+05; + case 6: return 1e+06; + case 7: return 1e+07; + case 8: return 1e+08; + case 9: return 1e+09; + case 10: return 1e+10; + case 11: return 1e+11; + case 12: return 1e+12; + case 13: return 1e+13; + case 14: return 1e+14; + case 15: return 1e+15; + default: + if (e > 15) { + double value = 1e+15; + while (e-- > 15) { value *= 10.0; } + return value; + } else { + SkASSERT(e < 0); + double value = 1.0; + while (e++ < 0) { value /= 10.0; } + return value; + } + } +} + +/** Write a string into result, includeing a terminating '\0' (for + unit testing). Return strlen(result) (for SkWStream::write) The + resulting string will be in the form /[-]?([0-9]*.)?[0-9]+/ and + sscanf(result, "%f", &x) will return the original value iff the + value is finite. This function accepts all possible input values. + + Motivation: "PDF does not support [numbers] in exponential format + (such as 6.02e23)." Otherwise, this function would rely on a + sprintf-type function from the standard library. */ +unsigned SkFloatToDecimal(float value, char result[kMaximumSkFloatToDecimalLength]) { + /* The longest result is -FLT_MIN. + We serialize it as "-.0000000000000000000000000000000000000117549435" + which has 48 characters plus a terminating '\0'. */ + + static_assert(kMaximumSkFloatToDecimalLength == 49, ""); + // 3 = '-', '.', and '\0' characters. + // 9 = number of significant digits + // abs(FLT_MIN_10_EXP) = number of zeros in FLT_MIN + static_assert(kMaximumSkFloatToDecimalLength == 3 + 9 - FLT_MIN_10_EXP, ""); + + /* section C.1 of the PDF1.4 spec (http://goo.gl/0SCswJ) says that + most PDF rasterizers will use fixed-point scalars that lack the + dynamic range of floats. Even if this is the case, I want to + serialize these (uncommon) very small and very large scalar + values with enough precision to allow a floating-point + rasterizer to read them in with perfect accuracy. + Experimentally, rasterizers such as pdfium do seem to benefit + from this. Rasterizers that rely on fixed-point scalars should + gracefully ignore these values that they can not parse. */ + char* output = &result[0]; + const char* const end = &result[kMaximumSkFloatToDecimalLength - 1]; + // subtract one to leave space for '\0'. + + /* This function is written to accept any possible input value, + including non-finite values such as INF and NAN. In that case, + we ignore value-correctness and and output a syntacticly-valid + number. */ + if (value == INFINITY) { + value = FLT_MAX; // nearest finite float. + } + if (value == -INFINITY) { + value = -FLT_MAX; // nearest finite float. + } + if (!std::isfinite(value) || value == 0.0f) { + // NAN is unsupported in PDF. Always output a valid number. + // Also catch zero here, as a special case. + *output++ = '0'; + *output = '\0'; + return static_cast<unsigned>(output - result); + } + if (value < 0.0) { + *output++ = '-'; + value = -value; + } + SkASSERT(value >= 0.0f); + + int binaryExponent; + (void)std::frexp(value, &binaryExponent); + static const double kLog2 = 0.3010299956639812; // log10(2.0); + int decimalExponent = static_cast<int>(std::floor(kLog2 * binaryExponent)); + int decimalShift = decimalExponent - 8; + double power = pow10(-decimalShift); + SkASSERT(value * power <= (double)INT_MAX); + int d = static_cast<int>(value * power + 0.5); + // SkASSERT(value == (float)(d * pow(10.0, decimalShift))); + SkASSERT(d <= 999999999); + if (d > 167772159) { // floor(pow(10,1+log10(1<<24))) + // need one fewer decimal digits for 24-bit precision. + decimalShift = decimalExponent - 7; + // SkASSERT(power * 0.1 = pow10(-decimalShift)); + // recalculate to get rounding right. + d = static_cast<int>(value * (power * 0.1) + 0.5); + SkASSERT(d <= 99999999); + } + while (d % 10 == 0) { + d /= 10; + ++decimalShift; + } + SkASSERT(d > 0); + // SkASSERT(value == (float)(d * pow(10.0, decimalShift))); + unsigned char buffer[9]; // decimal value buffer. + int bufferIndex = 0; + do { + buffer[bufferIndex++] = d % 10; + d /= 10; + } while (d != 0); + SkASSERT(bufferIndex <= (int)sizeof(buffer) && bufferIndex > 0); + if (decimalShift >= 0) { + do { + --bufferIndex; + *output++ = '0' + buffer[bufferIndex]; + } while (bufferIndex); + for (int i = 0; i < decimalShift; ++i) { + *output++ = '0'; + } + } else { + int placesBeforeDecimal = bufferIndex + decimalShift; + if (placesBeforeDecimal > 0) { + while (placesBeforeDecimal-- > 0) { + --bufferIndex; + *output++ = '0' + buffer[bufferIndex]; + } + *output++ = '.'; + } else { + *output++ = '.'; + int placesAfterDecimal = -placesBeforeDecimal; + while (placesAfterDecimal-- > 0) { + *output++ = '0'; + } + } + while (bufferIndex > 0) { + --bufferIndex; + *output++ = '0' + buffer[bufferIndex]; + if (output == end) { + break; // denormalized: don't need extra precision. + // Note: denormalized numbers will not have the same number of + // significantDigits, but do not need them to round-trip. + } + } + } + SkASSERT(output <= end); + *output = '\0'; + return static_cast<unsigned>(output - result); +} diff --git a/third_party/skia_shared/SkFloatToDecimal.h b/third_party/skia_shared/SkFloatToDecimal.h new file mode 100644 index 0000000000..ac1042dbfb --- /dev/null +++ b/third_party/skia_shared/SkFloatToDecimal.h @@ -0,0 +1,34 @@ +/* + * Copyright 2017 Google Inc. + * + * Use of this source code is governed by a BSD-style license that can be + * found in the LICENSE file. + */ + +#ifndef SkFloatToDecimal_DEFINED +#define SkFloatToDecimal_DEFINED + +constexpr unsigned kMaximumSkFloatToDecimalLength = 49; + +/** \fn SkFloatToDecimal + Convert a float into a decimal string. + + The resulting string will be in the form `[-]?([0-9]*\.)?[0-9]+` (It does + not use scientific notation.) and `sscanf(output, "%f", &x)` will return + the original value if the value is finite. This function accepts all + possible input values. + + INFINITY and -INFINITY are rounded to FLT_MAX and -FLT_MAX. + + NAN values are converted to 0. + + This function will always add a terminating '\0' to the output. + + @param value Any floating-point number + @param output The buffer to write the string into. Must be non-null. + + @return strlen(output) +*/ +unsigned SkFloatToDecimal(float value, char output[kMaximumSkFloatToDecimalLength]); + +#endif // SkFloatToDecimal_DEFINED |