1 // Copyright 2019 The PDFium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "core/fpdfapi/edit/cpdf_contentstream_write_utils.h"
6
7 #include <cassert>
8 #include <cfloat>
9 #include <climits>
10 #include <cmath>
11 #include <ostream>
12
13 #include "core/fxcrt/compiler_specific.h"
14 #include "core/fxcrt/span.h"
15
16 namespace {
17
18 constexpr unsigned kMaximumSkFloatToDecimalLength = 49;
19
20 // Return pow(10.0, e), optimized for common cases.
pow10(int e)21 double pow10(int e) {
22 switch (e) {
23 case 0:
24 return 1.0; // common cases
25 case 1:
26 return 10.0;
27 case 2:
28 return 100.0;
29 case 3:
30 return 1e+03;
31 case 4:
32 return 1e+04;
33 case 5:
34 return 1e+05;
35 case 6:
36 return 1e+06;
37 case 7:
38 return 1e+07;
39 case 8:
40 return 1e+08;
41 case 9:
42 return 1e+09;
43 case 10:
44 return 1e+10;
45 case 11:
46 return 1e+11;
47 case 12:
48 return 1e+12;
49 case 13:
50 return 1e+13;
51 case 14:
52 return 1e+14;
53 case 15:
54 return 1e+15;
55 default:
56 if (e > 15) {
57 double value = 1e+15;
58 while (e-- > 15) {
59 value *= 10.0;
60 }
61 return value;
62 } else {
63 assert(e < 0);
64 double value = 1.0;
65 while (e++ < 0) {
66 value /= 10.0;
67 }
68 return value;
69 }
70 }
71 }
72
73 // SkFloatToDecimal
74 //
75 // Convert a float into a decimal string.
76 //
77 // The resulting string will be in the form `[-]?([0-9]*\.)?[0-9]+` (It does
78 // not use scientific notation.) and `sscanf(output, "%f", &x)` will return
79 // the original value if the value is finite. This function accepts all
80 // possible input values.
81 //
82 // INFINITY and -INFINITY are rounded to FLT_MAX and -FLT_MAX.
83 //
84 // NAN values are converted to 0.
85 //
86 // This function will always add a terminating '\0' to the output.
87 //
88 // @param value Any floating-point number
89 // @param output The buffer to write the string into. Must be non-null.
90 //
91 // @return strlen(output)
92 //
93 // Write a string into output, including a terminating '\0' (for
94 // unit testing). Return strlen(output) (for SkWStream::write) The
95 // resulting string will be in the form /[-]?([0-9]*.)?[0-9]+/ and
96 // sscanf(output, "%f", &x) will return the original value iff the
97 // value is finite. This function accepts all possible input values.
98 //
99 // Motivation: "PDF does not support [numbers] in exponential format
100 // (such as 6.02e23)." Otherwise, this function would rely on a
101 // sprintf-type function from the standard library.
SkFloatToDecimal(float value,pdfium::span<char,kMaximumSkFloatToDecimalLength> output)102 unsigned SkFloatToDecimal(
103 float value,
104 pdfium::span<char, kMaximumSkFloatToDecimalLength> output) {
105 // The longest result is -FLT_MIN.
106 // We serialize it as "-.0000000000000000000000000000000000000117549435"
107 // which has 48 characters plus a terminating '\0'.
108 static_assert(kMaximumSkFloatToDecimalLength == 49, "");
109
110 // 3 = '-', '.', and '\0' characters.
111 // 9 = number of significant digits
112 // abs(FLT_MIN_10_EXP) = number of zeros in FLT_MIN
113 static_assert(kMaximumSkFloatToDecimalLength == 3 + 9 - FLT_MIN_10_EXP, "");
114
115 // section C.1 of the PDF 1.4 spec (http://goo.gl/0SCswJ) says that
116 // most PDF rasterizers will use fixed-point scalars that lack the
117 // dynamic range of floats. Even if this is the case, I want to
118 // serialize these (uncommon) very small and very large scalar
119 // values with enough precision to allow a floating-point
120 // rasterizer to read them in with perfect accuracy.
121 // Experimentally, rasterizers such as pdfium do seem to benefit
122 // from this. Rasterizers that rely on fixed-point scalars should
123 // gracefully ignore these values that they can not parse.
124 char* output_ptr = output.data();
125
126 // last(1) leaves space for '\0'.
127 const char* const end = output.last(1u).data();
128
129 // This function is written to accept any possible input value,
130 // including non-finite values such as INF and NAN. In that case,
131 // we ignore value-correctness and output a syntacticly-valid
132 // number.
133 if (value == INFINITY) {
134 value = FLT_MAX; // nearest finite float.
135 }
136 if (value == -INFINITY) {
137 value = -FLT_MAX; // nearest finite float.
138 }
139 UNSAFE_TODO({
140 if (!std::isfinite(value) || value == 0.0f) {
141 // NAN is unsupported in PDF. Always output a valid number.
142 // Also catch zero here, as a special case.
143 *output_ptr++ = '0';
144 *output_ptr = '\0';
145 return static_cast<unsigned>(output_ptr - output.data());
146 }
147 if (value < 0.0) {
148 *output_ptr++ = '-';
149 value = -value;
150 }
151 assert(value >= 0.0f);
152
153 int binaryExponent;
154 (void)std::frexp(value, &binaryExponent);
155 static const double kLog2 = 0.3010299956639812; // log10(2.0);
156 int decimalExponent = static_cast<int>(std::floor(kLog2 * binaryExponent));
157 int decimalShift = decimalExponent - 8;
158 double power = pow10(-decimalShift);
159 assert(value * power <= (double)INT_MAX);
160 int d = static_cast<int>(value * power + 0.5);
161 // assert(value == (float)(d * pow(10.0, decimalShift)));
162 assert(d <= 999999999);
163 if (d > 167772159) { // floor(pow(10,1+log10(1<<24)))
164 // need one fewer decimal digits for 24-bit precision.
165 decimalShift = decimalExponent - 7;
166 // assert(power * 0.1 = pow10(-decimalShift));
167 // recalculate to get rounding right.
168 d = static_cast<int>(value * (power * 0.1) + 0.5);
169 assert(d <= 99999999);
170 }
171 while (d % 10 == 0) {
172 d /= 10;
173 ++decimalShift;
174 }
175 assert(d > 0);
176 // assert(value == (float)(d * pow(10.0, decimalShift)));
177 unsigned char buffer[9]; // decimal value buffer.
178 int bufferIndex = 0;
179 do {
180 buffer[bufferIndex++] = d % 10;
181 d /= 10;
182 } while (d != 0);
183 assert(bufferIndex <= (int)sizeof(buffer) && bufferIndex > 0);
184 if (decimalShift >= 0) {
185 do {
186 --bufferIndex;
187 *output_ptr++ = '0' + buffer[bufferIndex];
188 } while (bufferIndex);
189 for (int i = 0; i < decimalShift; ++i) {
190 *output_ptr++ = '0';
191 }
192 } else {
193 int placesBeforeDecimal = bufferIndex + decimalShift;
194 if (placesBeforeDecimal > 0) {
195 while (placesBeforeDecimal-- > 0) {
196 --bufferIndex;
197 *output_ptr++ = '0' + buffer[bufferIndex];
198 }
199 *output_ptr++ = '.';
200 } else {
201 *output_ptr++ = '.';
202 int placesAfterDecimal = -placesBeforeDecimal;
203 while (placesAfterDecimal-- > 0) {
204 *output_ptr++ = '0';
205 }
206 }
207 while (bufferIndex > 0) {
208 --bufferIndex;
209 *output_ptr++ = '0' + buffer[bufferIndex];
210 if (output_ptr == end) {
211 break; // denormalized: don't need extra precision.
212 // Note: denormalized numbers will not have the same number
213 // of significantDigits, but do not need them to round-trip.
214 }
215 }
216 }
217 assert(output_ptr <= end);
218 *output_ptr = '\0';
219 return static_cast<unsigned>(output_ptr - output.data());
220 });
221 }
222
223 } // namespace
224
WriteFloat(std::ostream & stream,float value)225 std::ostream& WriteFloat(std::ostream& stream, float value) {
226 char buffer[kMaximumSkFloatToDecimalLength];
227 unsigned size = SkFloatToDecimal(value, buffer);
228 stream.write(buffer, size);
229 return stream;
230 }
231
WriteMatrix(std::ostream & stream,const CFX_Matrix & matrix)232 std::ostream& WriteMatrix(std::ostream& stream, const CFX_Matrix& matrix) {
233 WriteFloat(stream, matrix.a) << " ";
234 WriteFloat(stream, matrix.b) << " ";
235 WriteFloat(stream, matrix.c) << " ";
236 WriteFloat(stream, matrix.d) << " ";
237 WriteFloat(stream, matrix.e) << " ";
238 WriteFloat(stream, matrix.f);
239 return stream;
240 }
241
WritePoint(std::ostream & stream,const CFX_PointF & point)242 std::ostream& WritePoint(std::ostream& stream, const CFX_PointF& point) {
243 WriteFloat(stream, point.x) << " ";
244 WriteFloat(stream, point.y);
245 return stream;
246 }
247
WriteRect(std::ostream & stream,const CFX_FloatRect & rect)248 std::ostream& WriteRect(std::ostream& stream, const CFX_FloatRect& rect) {
249 WriteFloat(stream, rect.left) << " ";
250 WriteFloat(stream, rect.bottom) << " ";
251 WriteFloat(stream, rect.Width()) << " ";
252 WriteFloat(stream, rect.Height());
253 return stream;
254 }
255