1 //===-- Fixed Point Converter for printf ------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef LLVM_LIBC_SRC_STDIO_PRINTF_CORE_FIXED_CONVERTER_H
10 #define LLVM_LIBC_SRC_STDIO_PRINTF_CORE_FIXED_CONVERTER_H
11
12 #include "include/llvm-libc-macros/stdfix-macros.h"
13 #include "src/__support/CPP/string_view.h"
14 #include "src/__support/fixed_point/fx_bits.h"
15 #include "src/__support/fixed_point/fx_rep.h"
16 #include "src/__support/integer_to_string.h"
17 #include "src/__support/libc_assert.h"
18 #include "src/stdio/printf_core/converter_utils.h"
19 #include "src/stdio/printf_core/core_structs.h"
20 #include "src/stdio/printf_core/writer.h"
21
22 #include <inttypes.h>
23 #include <stddef.h>
24
25 namespace LIBC_NAMESPACE {
26 namespace printf_core {
27
28 // This is just for assertions. It will be compiled out for release builds.
const_ten_exp(uint32_t exponent)29 LIBC_INLINE constexpr uint32_t const_ten_exp(uint32_t exponent) {
30 uint32_t result = 1;
31 LIBC_ASSERT(exponent < 11);
32 for (uint32_t i = 0; i < exponent; ++i)
33 result *= 10;
34
35 return result;
36 }
37
38 #define READ_FX_BITS(TYPE) \
39 do { \
40 auto fixed_bits = fixed_point::FXBits<TYPE>( \
41 fixed_point::FXRep<TYPE>::StorageType(to_conv.conv_val_raw)); \
42 integral = fixed_bits.get_integral(); \
43 fractional = fixed_bits.get_fraction(); \
44 exponent = fixed_bits.get_exponent(); \
45 is_negative = fixed_bits.get_sign(); \
46 } while (false)
47
48 #define APPLY_FX_LENGTH_MODIFIER(LENGTH_MODIFIER) \
49 do { \
50 if (to_conv.conv_name == 'r') { \
51 READ_FX_BITS(LENGTH_MODIFIER fract); \
52 } else if (to_conv.conv_name == 'R') { \
53 READ_FX_BITS(unsigned LENGTH_MODIFIER fract); \
54 } else if (to_conv.conv_name == 'k') { \
55 READ_FX_BITS(LENGTH_MODIFIER accum); \
56 } else if (to_conv.conv_name == 'K') { \
57 READ_FX_BITS(unsigned LENGTH_MODIFIER accum); \
58 } else { \
59 LIBC_ASSERT(false && "Invalid conversion name passed to convert_fixed"); \
60 return FIXED_POINT_CONVERSION_ERROR; \
61 } \
62 } while (false)
63
convert_fixed(Writer * writer,const FormatSection & to_conv)64 LIBC_INLINE int convert_fixed(Writer *writer, const FormatSection &to_conv) {
65 // Long accum should be the largest type, so we can store all the smaller
66 // numbers in things sized for it.
67 using LARep = fixed_point::FXRep<unsigned long accum>;
68 using StorageType = LARep::StorageType;
69
70 // All of the letters will be defined relative to variable a, which will be
71 // the appropriate case based on the name of the conversion. This converts any
72 // conversion name into the letter 'a' with the appropriate case.
73 const char a = (to_conv.conv_name & 32) | 'A';
74 FormatFlags flags = to_conv.flags;
75
76 bool is_negative;
77 int exponent;
78 StorageType integral;
79 StorageType fractional;
80
81 // r = fract
82 // k = accum
83 // lowercase = signed
84 // uppercase = unsigned
85 // h = short
86 // l = long
87 // any other length modifier has no effect
88
89 if (to_conv.length_modifier == LengthModifier::h) {
90 APPLY_FX_LENGTH_MODIFIER(short);
91 } else if (to_conv.length_modifier == LengthModifier::l) {
92 APPLY_FX_LENGTH_MODIFIER(long);
93 } else {
94 APPLY_FX_LENGTH_MODIFIER();
95 }
96
97 LIBC_ASSERT(static_cast<size_t>(exponent) <=
98 (sizeof(StorageType) - sizeof(uint32_t)) * CHAR_BIT &&
99 "StorageType must be large enough to hold the fractional "
100 "component multiplied by a 32 bit number.");
101
102 // If to_conv doesn't specify a precision, the precision defaults to 6.
103 const size_t precision = to_conv.precision < 0 ? 6 : to_conv.precision;
104 bool has_decimal_point =
105 (precision > 0) || ((flags & FormatFlags::ALTERNATE_FORM) != 0);
106
107 // The number of non-zero digits below the decimal point for a negative power
108 // of 2 in base 10 is equal to the magnitude of the power of 2.
109
110 // A quick proof:
111 // Let p be any positive integer.
112 // Let e = 2^(-p)
113 // Let t be a positive integer such that e * 10^t is an integer.
114 // By definition: The smallest allowed value of t must be equal to the number
115 // of non-zero digits below the decimal point in e.
116 // If we evaluate e * 10^t we get the following:
117 // e * 10^t = 2^(-p) * 10*t = 2^(-p) * 2^t * 5^t = 5^t * 2^(t-p)
118 // For 5^t * 2^(t-p) to be an integer, both exponents must be non-negative,
119 // since 5 and 2 are coprime.
120 // The smallest value of t such that t-p is non-negative is p.
121 // Therefor, the number of non-zero digits below the decimal point for a given
122 // negative power of 2 "p" is equal to the value of p.
123
124 constexpr size_t MAX_FRACTION_DIGITS = LARep::FRACTION_LEN;
125
126 char fraction_digits[MAX_FRACTION_DIGITS];
127
128 size_t valid_fraction_digits = 0;
129
130 // TODO: Factor this part out
131 while (fractional > 0) {
132 uint32_t cur_digits = 0;
133 // 10^9 is used since it's the largest power of 10 that fits in a uint32_t
134 constexpr uint32_t TEN_EXP_NINE = 1000000000;
135 constexpr size_t DIGITS_PER_BLOCK = 9;
136
137 // Multiply by 10^9, then grab the digits above the decimal point, then
138 // clear those digits in fractional.
139 fractional = fractional * TEN_EXP_NINE;
140 cur_digits = static_cast<uint32_t>(fractional >> exponent);
141 fractional = fractional % (StorageType(1) << exponent);
142
143 // we add TEN_EXP_NINE to force leading zeroes to show up, then we skip the
144 // first digit in the loop.
145 const IntegerToString<uint32_t> cur_fractional_digits(cur_digits +
146 TEN_EXP_NINE);
147 for (size_t i = 0;
148 i < DIGITS_PER_BLOCK && valid_fraction_digits < MAX_FRACTION_DIGITS;
149 ++i, ++valid_fraction_digits)
150 fraction_digits[valid_fraction_digits] =
151 cur_fractional_digits.view()[i + 1];
152
153 if (valid_fraction_digits >= MAX_FRACTION_DIGITS) {
154 LIBC_ASSERT(fractional == 0 && "If the fraction digit buffer is full, "
155 "there should be no remaining digits.");
156 /*
157 A visual explanation of what this assert is checking:
158
159 32 digits (max for 32 bit fract)
160 +------------------------------++--+--- must be zero
161 | || |
162 123456789012345678901234567890120000
163 | || || || |
164 +-------++-------++-------++-------+
165 9 digit blocks
166 */
167 LIBC_ASSERT(cur_digits % const_ten_exp(
168 DIGITS_PER_BLOCK -
169 (MAX_FRACTION_DIGITS % DIGITS_PER_BLOCK)) ==
170 0 &&
171 "Digits after the MAX_FRACTION_DIGITS should all be zero.");
172 valid_fraction_digits = MAX_FRACTION_DIGITS;
173 }
174 }
175
176 if (precision < valid_fraction_digits) {
177 // Handle rounding. Just do round to nearest, tie to even since it's
178 // unspecified.
179 RoundDirection round;
180 char first_digit_after = fraction_digits[precision];
181 if (first_digit_after > '5') {
182 round = RoundDirection::Up;
183 } else if (first_digit_after < '5') {
184 round = RoundDirection::Down;
185 } else {
186 // first_digit_after == '5'
187 // need to check the remaining digits, but default to even.
188 round = RoundDirection::Even;
189 for (size_t cur_digit_index = precision + 1;
190 cur_digit_index + 1 < valid_fraction_digits; ++cur_digit_index) {
191 if (fraction_digits[cur_digit_index] != '0') {
192 round = RoundDirection::Up;
193 break;
194 }
195 }
196 }
197
198 // If we need to actually perform rounding, do so.
199 if (round == RoundDirection::Up || round == RoundDirection::Even) {
200 bool keep_rounding = true;
201 int digit_to_round = static_cast<int>(precision) - 1;
202 for (; digit_to_round >= 0 && keep_rounding; --digit_to_round) {
203 keep_rounding = false;
204 char cur_digit = fraction_digits[digit_to_round];
205 // if the digit should not be rounded up
206 if (round == RoundDirection::Even && ((cur_digit - '0') % 2) == 0) {
207 // break out of the loop
208 break;
209 }
210 fraction_digits[digit_to_round] += 1;
211
212 // if the digit was a 9, instead replace with a 0.
213 if (cur_digit == '9') {
214 fraction_digits[digit_to_round] = '0';
215 keep_rounding = true;
216 }
217 }
218
219 // if every digit below the decimal point was rounded up but we need to
220 // keep rounding
221 if (keep_rounding &&
222 (round == RoundDirection::Up ||
223 (round == RoundDirection::Even && ((integral % 2) == 1)))) {
224 // add one to the integral portion to round it up.
225 ++integral;
226 }
227 }
228
229 valid_fraction_digits = precision;
230 }
231
232 const IntegerToString<StorageType> integral_str(integral);
233
234 // these are signed to prevent underflow due to negative values. The
235 // eventual values will always be non-negative.
236 size_t trailing_zeroes = 0;
237 int padding;
238
239 // If the precision is greater than the actual result, pad with 0s
240 if (precision > valid_fraction_digits)
241 trailing_zeroes = precision - (valid_fraction_digits);
242
243 constexpr cpp::string_view DECIMAL_POINT(".");
244
245 char sign_char = 0;
246
247 // Check if the conv name is uppercase
248 if (a == 'A') {
249 // These flags are only for signed conversions, so this removes them if the
250 // conversion is unsigned.
251 flags = FormatFlags(flags &
252 ~(FormatFlags::FORCE_SIGN | FormatFlags::SPACE_PREFIX));
253 }
254
255 if (is_negative)
256 sign_char = '-';
257 else if ((flags & FormatFlags::FORCE_SIGN) == FormatFlags::FORCE_SIGN)
258 sign_char = '+'; // FORCE_SIGN has precedence over SPACE_PREFIX
259 else if ((flags & FormatFlags::SPACE_PREFIX) == FormatFlags::SPACE_PREFIX)
260 sign_char = ' ';
261
262 padding = static_cast<int>(to_conv.min_width - (sign_char > 0 ? 1 : 0) -
263 integral_str.size() -
264 static_cast<int>(has_decimal_point) -
265 valid_fraction_digits - trailing_zeroes);
266 if (padding < 0)
267 padding = 0;
268
269 if ((flags & FormatFlags::LEFT_JUSTIFIED) == FormatFlags::LEFT_JUSTIFIED) {
270 // The pattern is (sign), integral, (.), (fraction), (zeroes), (spaces)
271 if (sign_char > 0)
272 RET_IF_RESULT_NEGATIVE(writer->write(sign_char));
273 RET_IF_RESULT_NEGATIVE(writer->write(integral_str.view()));
274 if (has_decimal_point)
275 RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
276 if (valid_fraction_digits > 0)
277 RET_IF_RESULT_NEGATIVE(
278 writer->write({fraction_digits, valid_fraction_digits}));
279 if (trailing_zeroes > 0)
280 RET_IF_RESULT_NEGATIVE(writer->write('0', trailing_zeroes));
281 if (padding > 0)
282 RET_IF_RESULT_NEGATIVE(writer->write(' ', padding));
283 } else {
284 // The pattern is (spaces), (sign), (zeroes), integral, (.), (fraction),
285 // (zeroes)
286 if ((padding > 0) &&
287 ((flags & FormatFlags::LEADING_ZEROES) != FormatFlags::LEADING_ZEROES))
288 RET_IF_RESULT_NEGATIVE(writer->write(' ', padding));
289 if (sign_char > 0)
290 RET_IF_RESULT_NEGATIVE(writer->write(sign_char));
291 if ((padding > 0) &&
292 ((flags & FormatFlags::LEADING_ZEROES) == FormatFlags::LEADING_ZEROES))
293 RET_IF_RESULT_NEGATIVE(writer->write('0', padding));
294 RET_IF_RESULT_NEGATIVE(writer->write(integral_str.view()));
295 if (has_decimal_point)
296 RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
297 if (valid_fraction_digits > 0)
298 RET_IF_RESULT_NEGATIVE(
299 writer->write({fraction_digits, valid_fraction_digits}));
300 if (trailing_zeroes > 0)
301 RET_IF_RESULT_NEGATIVE(writer->write('0', trailing_zeroes));
302 }
303 return WRITE_OK;
304 }
305
306 } // namespace printf_core
307 } // namespace LIBC_NAMESPACE
308
309 #endif // LLVM_LIBC_SRC_STDIO_PRINTF_CORE_FIXED_CONVERTER_H
310