GCC Code Coverage Report

Directory: libs/json/include/boost/json/
File: detail/ryu/impl/d2s.ipp
Date: 2025-12-23 17:20:53
Exec Total Coverage
Lines: 224 225 99.6%
Functions: 7 7 100.0%
Branches: 116 122 95.1%
Line Branch Exec Source
1 // Copyright 2018 Ulf Adams
2 //
3 // The contents of this file may be used under the terms of the Apache License,
4 // Version 2.0.
5 //
6 // (See accompanying file LICENSE-Apache or copy at
7 // http://www.apache.org/licenses/LICENSE-2.0)
8 //
9 // Alternatively, the contents of this file may be used under the terms of
10 // the Boost Software License, Version 1.0.
11 // (See accompanying file LICENSE-Boost or copy at
12 // https://www.boost.org/LICENSE_1_0.txt)
13 //
14 // Unless required by applicable law or agreed to in writing, this software
15 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16 // KIND, either express or implied.
17
18 // Runtime compiler options:
19 // -DRYU_DEBUG Generate verbose debugging output to stdout.
20 //
21 // -DRYU_ONLY_64_BIT_OPS Avoid using uint128_t or 64-bit intrinsics. Slower,
22 // depending on your compiler.
23 //
24 // -DRYU_OPTIMIZE_SIZE Use smaller lookup tables. Instead of storing every
25 // required power of 5, only store every 26th entry, and compute
26 // intermediate values with a multiplication. This reduces the lookup table
27 // size by about 10x (only one case, and only double) at the cost of some
28 // performance. Currently requires MSVC intrinsics.
29
30 /*
31 This is a derivative work
32 */
33
34 #ifndef BOOST_JSON_DETAIL_RYU_IMPL_D2S_IPP
35 #define BOOST_JSON_DETAIL_RYU_IMPL_D2S_IPP
36
37 #include <boost/json/detail/ryu/ryu.hpp>
38 #include <cstdlib>
39 #include <cstring>
40
41 #ifdef RYU_DEBUG
42 #include <stdio.h>
43 #endif
44
45 // ABSL avoids uint128_t on Win32 even if __SIZEOF_INT128__ is defined.
46 // Let's do the same for now.
47 #if defined(__SIZEOF_INT128__) && !defined(_MSC_VER) && !defined(RYU_ONLY_64_BIT_OPS)
48 #define BOOST_JSON_RYU_HAS_UINT128
49 #elif defined(_MSC_VER) && !defined(RYU_ONLY_64_BIT_OPS) && defined(_M_X64)
50 #define BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS
51 #endif
52
53 #include <boost/json/detail/ryu/detail/common.hpp>
54 #include <boost/json/detail/ryu/detail/digit_table.hpp>
55 #include <boost/json/detail/ryu/detail/d2s.hpp>
56 #include <boost/json/detail/ryu/detail/d2s_intrinsics.hpp>
57
58 namespace boost {
59 namespace json {
60 namespace detail {
61
62 namespace ryu {
63 namespace detail {
64
65 // We need a 64x128-bit multiplication and a subsequent 128-bit shift.
66 // Multiplication:
67 // The 64-bit factor is variable and passed in, the 128-bit factor comes
68 // from a lookup table. We know that the 64-bit factor only has 55
69 // significant bits (i.e., the 9 topmost bits are zeros). The 128-bit
70 // factor only has 124 significant bits (i.e., the 4 topmost bits are
71 // zeros).
72 // Shift:
73 // In principle, the multiplication result requires 55 + 124 = 179 bits to
74 // represent. However, we then shift this value to the right by j, which is
75 // at least j >= 115, so the result is guaranteed to fit into 179 - 115 = 64
76 // bits. This means that we only need the topmost 64 significant bits of
77 // the 64x128-bit multiplication.
78 //
79 // There are several ways to do this:
80 // 1. Best case: the compiler exposes a 128-bit type.
81 // We perform two 64x64-bit multiplications, add the higher 64 bits of the
82 // lower result to the higher result, and shift by j - 64 bits.
83 //
84 // We explicitly cast from 64-bit to 128-bit, so the compiler can tell
85 // that these are only 64-bit inputs, and can map these to the best
86 // possible sequence of assembly instructions.
87 // x64 machines happen to have matching assembly instructions for
88 // 64x64-bit multiplications and 128-bit shifts.
89 //
90 // 2. Second best case: the compiler exposes intrinsics for the x64 assembly
91 // instructions mentioned in 1.
92 //
93 // 3. We only have 64x64 bit instructions that return the lower 64 bits of
94 // the result, i.e., we have to use plain C.
95 // Our inputs are less than the full width, so we have three options:
96 // a. Ignore this fact and just implement the intrinsics manually.
97 // b. Split both into 31-bit pieces, which guarantees no internal overflow,
98 // but requires extra work upfront (unless we change the lookup table).
99 // c. Split only the first factor into 31-bit pieces, which also guarantees
100 // no internal overflow, but requires extra work since the intermediate
101 // results are not perfectly aligned.
102 #if defined(BOOST_JSON_RYU_HAS_UINT128)
103
104 // Best case: use 128-bit type.
105 inline
106 std::uint64_t
107 786 mulShift(
108 const std::uint64_t m,
109 const std::uint64_t* const mul,
110 const std::int32_t j) noexcept
111 {
112 786 const uint128_t b0 = ((uint128_t) m) * mul[0];
113 786 const uint128_t b2 = ((uint128_t) m) * mul[1];
114 786 return (std::uint64_t) (((b0 >> 64) + b2) >> (j - 64));
115 }
116
117 inline
118 uint64_t
119 262 mulShiftAll(
120 const std::uint64_t m,
121 const std::uint64_t* const mul,
122 std::int32_t const j,
123 std::uint64_t* const vp,
124 std::uint64_t* const vm,
125 const std::uint32_t mmShift) noexcept
126 {
127 // m <<= 2;
128 // uint128_t b0 = ((uint128_t) m) * mul[0]; // 0
129 // uint128_t b2 = ((uint128_t) m) * mul[1]; // 64
130 //
131 // uint128_t hi = (b0 >> 64) + b2;
132 // uint128_t lo = b0 & 0xffffffffffffffffull;
133 // uint128_t factor = (((uint128_t) mul[1]) << 64) + mul[0];
134 // uint128_t vpLo = lo + (factor << 1);
135 // *vp = (std::uint64_t) ((hi + (vpLo >> 64)) >> (j - 64));
136 // uint128_t vmLo = lo - (factor << mmShift);
137 // *vm = (std::uint64_t) ((hi + (vmLo >> 64) - (((uint128_t) 1ull) << 64)) >> (j - 64));
138 // return (std::uint64_t) (hi >> (j - 64));
139 262 *vp = mulShift(4 * m + 2, mul, j);
140 262 *vm = mulShift(4 * m - 1 - mmShift, mul, j);
141 262 return mulShift(4 * m, mul, j);
142 }
143
144 #elif defined(BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS)
145
146 inline
147 std::uint64_t
148 mulShift(
149 const std::uint64_t m,
150 const std::uint64_t* const mul,
151 const std::int32_t j) noexcept
152 {
153 // m is maximum 55 bits
154 std::uint64_t high1; // 128
155 std::uint64_t const low1 = umul128(m, mul[1], &high1); // 64
156 std::uint64_t high0; // 64
157 umul128(m, mul[0], &high0); // 0
158 std::uint64_t const sum = high0 + low1;
159 if (sum < high0)
160 ++high1; // overflow into high1
161 return shiftright128(sum, high1, j - 64);
162 }
163
164 inline
165 std::uint64_t
166 mulShiftAll(
167 const std::uint64_t m,
168 const std::uint64_t* const mul,
169 const std::int32_t j,
170 std::uint64_t* const vp,
171 std::uint64_t* const vm,
172 const std::uint32_t mmShift) noexcept
173 {
174 *vp = mulShift(4 * m + 2, mul, j);
175 *vm = mulShift(4 * m - 1 - mmShift, mul, j);
176 return mulShift(4 * m, mul, j);
177 }
178
179 #else // !defined(BOOST_JSON_RYU_HAS_UINT128) && !defined(BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS)
180
181 inline
182 std::uint64_t
183 mulShiftAll(
184 std::uint64_t m,
185 const std::uint64_t* const mul,
186 const std::int32_t j,
187 std::uint64_t* const vp,
188 std::uint64_t* const vm,
189 const std::uint32_t mmShift)
190 {
191 m <<= 1;
192 // m is maximum 55 bits
193 std::uint64_t tmp;
194 std::uint64_t const lo = umul128(m, mul[0], &tmp);
195 std::uint64_t hi;
196 std::uint64_t const mid = tmp + umul128(m, mul[1], &hi);
197 hi += mid < tmp; // overflow into hi
198
199 const std::uint64_t lo2 = lo + mul[0];
200 const std::uint64_t mid2 = mid + mul[1] + (lo2 < lo);
201 const std::uint64_t hi2 = hi + (mid2 < mid);
202 *vp = shiftright128(mid2, hi2, (std::uint32_t)(j - 64 - 1));
203
204 if (mmShift == 1)
205 {
206 const std::uint64_t lo3 = lo - mul[0];
207 const std::uint64_t mid3 = mid - mul[1] - (lo3 > lo);
208 const std::uint64_t hi3 = hi - (mid3 > mid);
209 *vm = shiftright128(mid3, hi3, (std::uint32_t)(j - 64 - 1));
210 }
211 else
212 {
213 const std::uint64_t lo3 = lo + lo;
214 const std::uint64_t mid3 = mid + mid + (lo3 < lo);
215 const std::uint64_t hi3 = hi + hi + (mid3 < mid);
216 const std::uint64_t lo4 = lo3 - mul[0];
217 const std::uint64_t mid4 = mid3 - mul[1] - (lo4 > lo3);
218 const std::uint64_t hi4 = hi3 - (mid4 > mid3);
219 *vm = shiftright128(mid4, hi4, (std::uint32_t)(j - 64));
220 }
221
222 return shiftright128(mid, hi, (std::uint32_t)(j - 64 - 1));
223 }
224
225 #endif // BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS
226
227 inline
228 std::uint32_t
229 538 decimalLength17(
230 const std::uint64_t v)
231 {
232 // This is slightly faster than a loop.
233 // The average output length is 16.38 digits, so we check high-to-low.
234 // Function precondition: v is not an 18, 19, or 20-digit number.
235 // (17 digits are sufficient for round-tripping.)
236
1/2
✗ Branch 0 not taken.
✓ Branch 1 taken 538 times.
 538 BOOST_ASSERT(v < 100000000000000000L);
237
2/2
✓ Branch 0 taken 10 times.
✓ Branch 1 taken 528 times.
 538 if (v >= 10000000000000000L) { return 17; }
238
2/2
✓ Branch 0 taken 19 times.
✓ Branch 1 taken 509 times.
 528 if (v >= 1000000000000000L) { return 16; }
239
2/2
✓ Branch 0 taken 4 times.
✓ Branch 1 taken 505 times.
 509 if (v >= 100000000000000L) { return 15; }
240
2/2
✓ Branch 0 taken 5 times.
✓ Branch 1 taken 500 times.
 505 if (v >= 10000000000000L) { return 14; }
241
2/2
✓ Branch 0 taken 6 times.
✓ Branch 1 taken 494 times.
 500 if (v >= 1000000000000L) { return 13; }
242
2/2
✓ Branch 0 taken 5 times.
✓ Branch 1 taken 489 times.
 494 if (v >= 100000000000L) { return 12; }
243
2/2
✓ Branch 0 taken 5 times.
✓ Branch 1 taken 484 times.
 489 if (v >= 10000000000L) { return 11; }
244
2/2
✓ Branch 0 taken 10 times.
✓ Branch 1 taken 474 times.
 484 if (v >= 1000000000L) { return 10; }
245
2/2
✓ Branch 0 taken 7 times.
✓ Branch 1 taken 467 times.
 474 if (v >= 100000000L) { return 9; }
246
2/2
✓ Branch 0 taken 6 times.
✓ Branch 1 taken 461 times.
 467 if (v >= 10000000L) { return 8; }
247
2/2
✓ Branch 0 taken 6 times.
✓ Branch 1 taken 455 times.
 461 if (v >= 1000000L) { return 7; }
248
2/2
✓ Branch 0 taken 5 times.
✓ Branch 1 taken 450 times.
 455 if (v >= 100000L) { return 6; }
249
2/2
✓ Branch 0 taken 5 times.
✓ Branch 1 taken 445 times.
 450 if (v >= 10000L) { return 5; }
250
2/2
✓ Branch 0 taken 6 times.
✓ Branch 1 taken 439 times.
 445 if (v >= 1000L) { return 4; }
251
2/2
✓ Branch 0 taken 18 times.
✓ Branch 1 taken 421 times.
 439 if (v >= 100L) { return 3; }
252
2/2
✓ Branch 0 taken 6 times.
✓ Branch 1 taken 415 times.
 421 if (v >= 10L) { return 2; }
253 415 return 1;
254 }
255
256 // A floating decimal representing m * 10^e.
257 struct floating_decimal_64
258 {
259 std::uint64_t mantissa;
260 // Decimal exponent's range is -324 to 308
261 // inclusive, and can fit in a short if needed.
262 std::int32_t exponent;
263 };
264
265 inline
266 floating_decimal_64
267 262 d2d(
268 const std::uint64_t ieeeMantissa,
269 const std::uint32_t ieeeExponent)
270 {
271 std::int32_t e2;
272 std::uint64_t m2;
273
2/2
✓ Branch 0 taken 15 times.
✓ Branch 1 taken 247 times.
 262 if (ieeeExponent == 0)
274 {
275 // We subtract 2 so that the bounds computation has 2 additional bits.
276 15 e2 = 1 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS - 2;
277 15 m2 = ieeeMantissa;
278 }
279 else
280 {
281 247 e2 = (std::int32_t)ieeeExponent - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS - 2;
282 247 m2 = (1ull << DOUBLE_MANTISSA_BITS) | ieeeMantissa;
283 }
284 262 const bool even = (m2 & 1) == 0;
285 262 const bool acceptBounds = even;
286
287 #ifdef RYU_DEBUG
288 printf("-> %" PRIu64 " * 2^%d\n", m2, e2 + 2);
289 #endif
290
291 // Step 2: Determine the interval of valid decimal representations.
292 262 const std::uint64_t mv = 4 * m2;
293 // Implicit bool -> int conversion. True is 1, false is 0.
294
4/4
✓ Branch 0 taken 9 times.
✓ Branch 1 taken 253 times.
✓ Branch 2 taken 1 times.
✓ Branch 3 taken 8 times.
 262 const std::uint32_t mmShift = ieeeMantissa != 0 || ieeeExponent <= 1;
295 // We would compute mp and mm like this:
296 // uint64_t mp = 4 * m2 + 2;
297 // uint64_t mm = mv - 1 - mmShift;
298
299 // Step 3: Convert to a decimal power base using 128-bit arithmetic.
300 std::uint64_t vr, vp, vm;
301 std::int32_t e10;
302 262 bool vmIsTrailingZeros = false;
303 262 bool vrIsTrailingZeros = false;
304
2/2
✓ Branch 0 taken 128 times.
✓ Branch 1 taken 134 times.
 262 if (e2 >= 0) {
305 // I tried special-casing q == 0, but there was no effect on performance.
306 // This expression is slightly faster than max(0, log10Pow2(e2) - 1).
307 128 const std::uint32_t q = log10Pow2(e2) - (e2 > 3);
308 128 e10 = (std::int32_t)q;
309 128 const std::int32_t k = DOUBLE_POW5_INV_BITCOUNT + pow5bits((int32_t)q) - 1;
310 128 const std::int32_t i = -e2 + (std::int32_t)q + k;
311 #if defined(BOOST_JSON_RYU_OPTIMIZE_SIZE)
312 uint64_t pow5[2];
313 double_computeInvPow5(q, pow5);
314 vr = mulShiftAll(m2, pow5, i, &vp, &vm, mmShift);
315 #else
316 128 vr = mulShiftAll(m2, DOUBLE_POW5_INV_SPLIT()[q], i, &vp, &vm, mmShift);
317 #endif
318 #ifdef RYU_DEBUG
319 printf("%" PRIu64 " * 2^%d / 10^%u\n", mv, e2, q);
320 printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
321 #endif
322
2/2
✓ Branch 0 taken 114 times.
✓ Branch 1 taken 14 times.
 128 if (q <= 21)
323 {
324 // This should use q <= 22, but I think 21 is also safe. Smaller values
325 // may still be safe, but it's more difficult to reason about them.
326 // Only one of mp, mv, and mm can be a multiple of 5, if any.
327 114 const std::uint32_t mvMod5 = ((std::uint32_t)mv) - 5 * ((std::uint32_t)div5(mv));
328
2/2
✓ Branch 0 taken 86 times.
✓ Branch 1 taken 28 times.
 114 if (mvMod5 == 0)
329 {
330 86 vrIsTrailingZeros = multipleOfPowerOf5(mv, q);
331 }
332
2/2
✓ Branch 0 taken 11 times.
✓ Branch 1 taken 17 times.
 28 else if (acceptBounds)
333 {
334 // Same as min(e2 + (~mm & 1), pow5Factor(mm)) >= q
335 // <=> e2 + (~mm & 1) >= q && pow5Factor(mm) >= q
336 // <=> true && pow5Factor(mm) >= q, since e2 >= q.
337 11 vmIsTrailingZeros = multipleOfPowerOf5(mv - 1 - mmShift, q);
338 }
339 else
340 {
341 // Same as min(e2 + 1, pow5Factor(mp)) >= q.
342 17 vp -= multipleOfPowerOf5(mv + 2, q);
343 }
344 }
345 }
346 else
347 {
348 // This expression is slightly faster than max(0, log10Pow5(-e2) - 1).
349 134 const std::uint32_t q = log10Pow5(-e2) - (-e2 > 1);
350 134 e10 = (std::int32_t)q + e2;
351 134 const std::int32_t i = -e2 - (std::int32_t)q;
352 134 const std::int32_t k = pow5bits(i) - DOUBLE_POW5_BITCOUNT;
353 134 const std::int32_t j = (std::int32_t)q - k;
354 #if defined(BOOST_JSON_RYU_OPTIMIZE_SIZE)
355 std::uint64_t pow5[2];
356 double_computePow5(i, pow5);
357 vr = mulShiftAll(m2, pow5, j, &vp, &vm, mmShift);
358 #else
359 134 vr = mulShiftAll(m2, DOUBLE_POW5_SPLIT()[i], j, &vp, &vm, mmShift);
360 #endif
361 #ifdef RYU_DEBUG
362 printf("%" PRIu64 " * 5^%d / 10^%u\n", mv, -e2, q);
363 printf("%u %d %d %d\n", q, i, k, j);
364 printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
365 #endif
366
2/2
✓ Branch 0 taken 3 times.
✓ Branch 1 taken 131 times.
 134 if (q <= 1)
367 {
368 // {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits.
369 // mv = 4 * m2, so it always has at least two trailing 0 bits.
370 3 vrIsTrailingZeros = true;
371
1/2
✓ Branch 0 taken 3 times.
✗ Branch 1 not taken.
 3 if (acceptBounds)
372 {
373 // mm = mv - 1 - mmShift, so it has 1 trailing 0 bit iff mmShift == 1.
374 3 vmIsTrailingZeros = mmShift == 1;
375 }
376 else
377 {
378 // mp = mv + 2, so it always has at least one trailing 0 bit.
379 ✗ --vp;
380 }
381 }
382
2/2
✓ Branch 0 taken 96 times.
✓ Branch 1 taken 35 times.
 131 else if (q < 63)
383 {
384 // TODO(ulfjack): Use a tighter bound here.
385 // We want to know if the full product has at least q trailing zeros.
386 // We need to compute min(p2(mv), p5(mv) - e2) >= q
387 // <=> p2(mv) >= q && p5(mv) - e2 >= q
388 // <=> p2(mv) >= q (because -e2 >= q)
389 96 vrIsTrailingZeros = multipleOfPowerOf2(mv, q);
390 #ifdef RYU_DEBUG
391 printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
392 #endif
393 }
394 }
395 #ifdef RYU_DEBUG
396 printf("e10=%d\n", e10);
397 printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
398 printf("vm is trailing zeros=%s\n", vmIsTrailingZeros ? "true" : "false");
399 printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
400 #endif
401
402 // Step 4: Find the shortest decimal representation in the interval of valid representations.
403 262 std::int32_t removed = 0;
404 262 std::uint8_t lastRemovedDigit = 0;
405 std::uint64_t output;
406 // On average, we remove ~2 digits.
407
4/4
✓ Branch 0 taken 3 times.
✓ Branch 1 taken 259 times.
✓ Branch 2 taken 91 times.
✓ Branch 3 taken 168 times.
 262 if (vmIsTrailingZeros || vrIsTrailingZeros)
408 {
409 // General case, which happens rarely (~0.7%).
410 for (;;)
411 {
412 1663 const std::uint64_t vpDiv10 = div10(vp);
413 1663 const std::uint64_t vmDiv10 = div10(vm);
414
2/2
✓ Branch 0 taken 94 times.
✓ Branch 1 taken 1569 times.
 1663 if (vpDiv10 <= vmDiv10)
415 94 break;
416 1569 const std::uint32_t vmMod10 = ((std::uint32_t)vm) - 10 * ((std::uint32_t)vmDiv10);
417 1569 const std::uint64_t vrDiv10 = div10(vr);
418 1569 const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
419 1569 vmIsTrailingZeros &= vmMod10 == 0;
420 1569 vrIsTrailingZeros &= lastRemovedDigit == 0;
421 1569 lastRemovedDigit = (uint8_t)vrMod10;
422 1569 vr = vrDiv10;
423 1569 vp = vpDiv10;
424 1569 vm = vmDiv10;
425 1569 ++removed;
426 1569 }
427 #ifdef RYU_DEBUG
428 printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
429 printf("d-10=%s\n", vmIsTrailingZeros ? "true" : "false");
430 #endif
431
2/2
✓ Branch 0 taken 2 times.
✓ Branch 1 taken 92 times.
 94 if (vmIsTrailingZeros)
432 {
433 for (;;)
434 {
435 3 const std::uint64_t vmDiv10 = div10(vm);
436 3 const std::uint32_t vmMod10 = ((std::uint32_t)vm) - 10 * ((std::uint32_t)vmDiv10);
437
2/2
✓ Branch 0 taken 2 times.
✓ Branch 1 taken 1 times.
 3 if (vmMod10 != 0)
438 2 break;
439 1 const std::uint64_t vpDiv10 = div10(vp);
440 1 const std::uint64_t vrDiv10 = div10(vr);
441 1 const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
442 1 vrIsTrailingZeros &= lastRemovedDigit == 0;
443 1 lastRemovedDigit = (uint8_t)vrMod10;
444 1 vr = vrDiv10;
445 1 vp = vpDiv10;
446 1 vm = vmDiv10;
447 1 ++removed;
448 1 }
449 }
450 #ifdef RYU_DEBUG
451 printf("%" PRIu64 " %d\n", vr, lastRemovedDigit);
452 printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
453 #endif
454
5/6
✓ Branch 0 taken 91 times.
✓ Branch 1 taken 3 times.
✓ Branch 2 taken 1 times.
✓ Branch 3 taken 90 times.
✓ Branch 4 taken 1 times.
✗ Branch 5 not taken.
 94 if (vrIsTrailingZeros && lastRemovedDigit == 5 && vr % 2 == 0)
455 {
456 // Round even if the exact number is .....50..0.
457 1 lastRemovedDigit = 4;
458 }
459 // We need to take vr + 1 if vr is outside bounds or we need to round up.
460
5/8
✓ Branch 0 taken 1 times.
✓ Branch 1 taken 93 times.
✓ Branch 2 taken 1 times.
✗ Branch 3 not taken.
✓ Branch 4 taken 1 times.
✗ Branch 5 not taken.
✗ Branch 6 not taken.
✓ Branch 7 taken 94 times.
 94 output = vr + ((vr == vm && (!acceptBounds || !vmIsTrailingZeros)) || lastRemovedDigit >= 5);
461 94 }
462 else
463 {
464 // Specialized for the common case (~99.3%). Percentages below are relative to this.
465 168 bool roundUp = false;
466 168 const std::uint64_t vpDiv100 = div100(vp);
467 168 const std::uint64_t vmDiv100 = div100(vm);
468
2/2
✓ Branch 0 taken 161 times.
✓ Branch 1 taken 7 times.
 168 if (vpDiv100 > vmDiv100)
469 {
470 // Optimization: remove two digits at a time (~86.2%).
471 161 const std::uint64_t vrDiv100 = div100(vr);
472 161 const std::uint32_t vrMod100 = ((std::uint32_t)vr) - 100 * ((std::uint32_t)vrDiv100);
473 161 roundUp = vrMod100 >= 50;
474 161 vr = vrDiv100;
475 161 vp = vpDiv100;
476 161 vm = vmDiv100;
477 161 removed += 2;
478 }
479 // Loop iterations below (approximately), without optimization above:
480 // 0: 0.03%, 1: 13.8%, 2: 70.6%, 3: 14.0%, 4: 1.40%, 5: 0.14%, 6+: 0.02%
481 // Loop iterations below (approximately), with optimization above:
482 // 0: 70.6%, 1: 27.8%, 2: 1.40%, 3: 0.14%, 4+: 0.02%
483 for (;;)
484 {
485 2256 const std::uint64_t vpDiv10 = div10(vp);
486 2256 const std::uint64_t vmDiv10 = div10(vm);
487
2/2
✓ Branch 0 taken 168 times.
✓ Branch 1 taken 2088 times.
 2256 if (vpDiv10 <= vmDiv10)
488 168 break;
489 2088 const std::uint64_t vrDiv10 = div10(vr);
490 2088 const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
491 2088 roundUp = vrMod10 >= 5;
492 2088 vr = vrDiv10;
493 2088 vp = vpDiv10;
494 2088 vm = vmDiv10;
495 2088 ++removed;
496 2088 }
497 #ifdef RYU_DEBUG
498 printf("%" PRIu64 " roundUp=%s\n", vr, roundUp ? "true" : "false");
499 printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
500 #endif
501 // We need to take vr + 1 if vr is outside bounds or we need to round up.
502
4/4
✓ Branch 0 taken 119 times.
✓ Branch 1 taken 49 times.
✓ Branch 2 taken 6 times.
✓ Branch 3 taken 113 times.
 168 output = vr + (vr == vm || roundUp);
503 }
504 262 const std::int32_t exp = e10 + removed;
505
506 #ifdef RYU_DEBUG
507 printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
508 printf("O=%" PRIu64 "\n", output);
509 printf("EXP=%d\n", exp);
510 #endif
511
512 floating_decimal_64 fd;
513 262 fd.exponent = exp;
514 262 fd.mantissa = output;
515 262 return fd;
516 }
517
518 inline
519 int
520 538 to_chars(
521 const floating_decimal_64 v,
522 const bool sign,
523 char* const result)
524 {
525 // Step 5: Print the decimal representation.
526 538 int index = 0;
527
2/2
✓ Branch 0 taken 129 times.
✓ Branch 1 taken 409 times.
 538 if (sign)
528 129 result[index++] = '-';
529
530 538 std::uint64_t output = v.mantissa;
531 538 std::uint32_t const olength = decimalLength17(output);
532
533 #ifdef RYU_DEBUG
534 printf("DIGITS=%" PRIu64 "\n", v.mantissa);
535 printf("OLEN=%u\n", olength);
536 printf("EXP=%u\n", v.exponent + olength);
537 #endif
538
539 // Print the decimal digits.
540 // The following code is equivalent to:
541 // for (uint32_t i = 0; i < olength - 1; ++i) {
542 // const uint32_t c = output % 10; output /= 10;
543 // result[index + olength - i] = (char) ('0' + c);
544 // }
545 // result[index] = '0' + output % 10;
546
547 538 std::uint32_t i = 0;
548 // We prefer 32-bit operations, even on 64-bit platforms.
549 // We have at most 17 digits, and uint32_t can store 9 digits.
550 // If output doesn't fit into uint32_t, we cut off 8 digits,
551 // so the rest will fit into uint32_t.
552
2/2
✓ Branch 0 taken 59 times.
✓ Branch 1 taken 479 times.
 538 if ((output >> 32) != 0)
553 {
554 // Expensive 64-bit division.
555 59 std::uint64_t const q = div1e8(output);
556 59 std::uint32_t output2 = ((std::uint32_t)output) - 100000000 * ((std::uint32_t)q);
557 59 output = q;
558
559 59 const std::uint32_t c = output2 % 10000;
560 59 output2 /= 10000;
561 59 const std::uint32_t d = output2 % 10000;
562 59 const std::uint32_t c0 = (c % 100) << 1;
563 59 const std::uint32_t c1 = (c / 100) << 1;
564 59 const std::uint32_t d0 = (d % 100) << 1;
565 59 const std::uint32_t d1 = (d / 100) << 1;
566 59 std::memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c0, 2);
567 59 std::memcpy(result + index + olength - i - 3, DIGIT_TABLE() + c1, 2);
568 59 std::memcpy(result + index + olength - i - 5, DIGIT_TABLE() + d0, 2);
569 59 std::memcpy(result + index + olength - i - 7, DIGIT_TABLE() + d1, 2);
570 59 i += 8;
571 }
572 538 uint32_t output2 = (std::uint32_t)output;
573
2/2
✓ Branch 0 taken 100 times.
✓ Branch 1 taken 538 times.
 638 while (output2 >= 10000)
574 {
575 #ifdef __clang__ // https://bugs.llvm.org/show_bug.cgi?id=38217
576 const uint32_t c = output2 - 10000 * (output2 / 10000);
577 #else
578 100 const uint32_t c = output2 % 10000;
579 #endif
580 100 output2 /= 10000;
581 100 const uint32_t c0 = (c % 100) << 1;
582 100 const uint32_t c1 = (c / 100) << 1;
583 100 memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c0, 2);
584 100 memcpy(result + index + olength - i - 3, DIGIT_TABLE() + c1, 2);
585 100 i += 4;
586 }
587
2/2
✓ Branch 0 taken 69 times.
✓ Branch 1 taken 469 times.
 538 if (output2 >= 100) {
588 69 const uint32_t c = (output2 % 100) << 1;
589 69 output2 /= 100;
590 69 memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c, 2);
591 69 i += 2;
592 }
593
2/2
✓ Branch 0 taken 62 times.
✓ Branch 1 taken 476 times.
 538 if (output2 >= 10) {
594 62 const uint32_t c = output2 << 1;
595 // We can't use memcpy here: the decimal dot goes between these two digits.
596 62 result[index + olength - i] = DIGIT_TABLE()[c + 1];
597 62 result[index] = DIGIT_TABLE()[c];
598 }
599 else {
600 476 result[index] = (char)('0' + output2);
601 }
602
603 // Print decimal point if needed.
604
2/2
✓ Branch 0 taken 123 times.
✓ Branch 1 taken 415 times.
 538 if (olength > 1) {
605 123 result[index + 1] = '.';
606 123 index += olength + 1;
607 }
608 else {
609 415 ++index;
610 }
611
612 // Print the exponent.
613 538 result[index++] = 'E';
614 538 int32_t exp = v.exponent + (int32_t)olength - 1;
615
2/2
✓ Branch 0 taken 92 times.
✓ Branch 1 taken 446 times.
 538 if (exp < 0) {
616 92 result[index++] = '-';
617 92 exp = -exp;
618 }
619
620
2/2
✓ Branch 0 taken 33 times.
✓ Branch 1 taken 505 times.
 538 if (exp >= 100) {
621 33 const int32_t c = exp % 10;
622 33 memcpy(result + index, DIGIT_TABLE() + 2 * (exp / 10), 2);
623 33 result[index + 2] = (char)('0' + c);
624 33 index += 3;
625 }
626
2/2
✓ Branch 0 taken 180 times.
✓ Branch 1 taken 325 times.
 505 else if (exp >= 10) {
627 180 memcpy(result + index, DIGIT_TABLE() + 2 * exp, 2);
628 180 index += 2;
629 }
630 else {
631 325 result[index++] = (char)('0' + exp);
632 }
633
634 538 return index;
635 }
636
637 538 static inline bool d2d_small_int(const uint64_t ieeeMantissa, const uint32_t ieeeExponent,
638 floating_decimal_64* const v) {
639 538 const uint64_t m2 = (1ull << DOUBLE_MANTISSA_BITS) | ieeeMantissa;
640 538 const int32_t e2 = (int32_t) ieeeExponent - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS;
641
642
2/2
✓ Branch 0 taken 131 times.
✓ Branch 1 taken 407 times.
 538 if (e2 > 0) {
643 // f = m2 * 2^e2 >= 2^53 is an integer.
644 // Ignore this case for now.
645 131 return false;
646 }
647
648
2/2
✓ Branch 0 taken 92 times.
✓ Branch 1 taken 315 times.
 407 if (e2 < -52) {
649 // f < 1.
650 92 return false;
651 }
652
653 // Since 2^52 <= m2 < 2^53 and 0 <= -e2 <= 52: 1 <= f = m2 / 2^-e2 < 2^53.
654 // Test if the lower -e2 bits of the significand are 0, i.e. whether the fraction is 0.
655 315 const uint64_t mask = (1ull << -e2) - 1;
656 315 const uint64_t fraction = m2 & mask;
657
2/2
✓ Branch 0 taken 39 times.
✓ Branch 1 taken 276 times.
 315 if (fraction != 0) {
658 39 return false;
659 }
660
661 // f is an integer in the range [1, 2^53).
662 // Note: mantissa might contain trailing (decimal) 0's.
663 // Note: since 2^53 < 10^16, there is no need to adjust decimalLength17().
664 276 v->mantissa = m2 >> -e2;
665 276 v->exponent = 0;
666 276 return true;
667 }
668
669 } // detail
670
671 int
672 609 d2s_buffered_n(
673 double f,
674 char* result,
675 bool allow_infinity_and_nan) noexcept
676 {
677 using namespace detail;
678 // Step 1: Decode the floating-point number, and unify normalized and subnormal cases.
679 609 std::uint64_t const bits = double_to_bits(f);
680
681 #ifdef RYU_DEBUG
682 printf("IN=");
683 for (std::int32_t bit = 63; bit >= 0; --bit) {
684 printf("%d", (int)((bits >> bit) & 1));
685 }
686 printf("\n");
687 #endif
688
689 // Decode bits into sign, mantissa, and exponent.
690 609 const bool ieeeSign = ((bits >> (DOUBLE_MANTISSA_BITS + DOUBLE_EXPONENT_BITS)) & 1) != 0;
691 609 const std::uint64_t ieeeMantissa = bits & ((1ull << DOUBLE_MANTISSA_BITS) - 1);
692 609 const std::uint32_t ieeeExponent = (std::uint32_t)((bits >> DOUBLE_MANTISSA_BITS) & ((1u << DOUBLE_EXPONENT_BITS) - 1));
693 // Case distinction; exit early for the easy cases.
694
6/6
✓ Branch 0 taken 591 times.
✓ Branch 1 taken 18 times.
✓ Branch 2 taken 68 times.
✓ Branch 3 taken 523 times.
✓ Branch 4 taken 53 times.
✓ Branch 5 taken 15 times.
 609 if (ieeeExponent == ((1u << DOUBLE_EXPONENT_BITS) - 1u) || (ieeeExponent == 0 && ieeeMantissa == 0)) {
695 // We changed how special numbers are output by default
696
2/2
✓ Branch 0 taken 11 times.
✓ Branch 1 taken 60 times.
 71 if (allow_infinity_and_nan)
697 11 return copy_special_str(result, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
698 else
699 60 return copy_special_str_conforming(result, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
700
701 }
702
703 floating_decimal_64 v;
704 538 const bool isSmallInt = d2d_small_int(ieeeMantissa, ieeeExponent, &v);
705
2/2
✓ Branch 0 taken 276 times.
✓ Branch 1 taken 262 times.
 538 if (isSmallInt) {
706 // For small integers in the range [1, 2^53), v.mantissa might contain trailing (decimal) zeros.
707 // For scientific notation we need to move these zeros into the exponent.
708 // (This is not needed for fixed-point notation, so it might be beneficial to trim
709 // trailing zeros in to_chars only if needed - once fixed-point notation output is implemented.)
710 for (;;) {
711 698 std::uint64_t const q = div10(v.mantissa);
712 698 std::uint32_t const r = ((std::uint32_t) v.mantissa) - 10 * ((std::uint32_t) q);
713
2/2
✓ Branch 0 taken 276 times.
✓ Branch 1 taken 422 times.
 698 if (r != 0)
714 276 break;
715 422 v.mantissa = q;
716 422 ++v.exponent;
717 422 }
718 }
719 else {
720 262 v = d2d(ieeeMantissa, ieeeExponent);
721 }
722
723 538 return to_chars(v, ieeeSign, result);
724 }
725
726 } // ryu
727
728 } // detail
729 } // namespace json
730 } // namespace boost
731
732 #endif
733