Bug Summary

File:lib/Support/ScaledNumber.cpp
Location:line 172, column 5
Description:Assigned value is garbage or undefined

Annotated Source Code

1//==- lib/Support/ScaledNumber.cpp - Support for scaled numbers -*- C++ -*-===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Implementation of some scaled number algorithms.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Support/ScaledNumber.h"
15
16#include "llvm/ADT/APFloat.h"
17#include "llvm/Support/Debug.h"
18
19using namespace llvm;
20using namespace llvm::ScaledNumbers;
21
22std::pair<uint64_t, int16_t> ScaledNumbers::multiply64(uint64_t LHS,
23 uint64_t RHS) {
24 // Separate into two 32-bit digits (U.L).
25 auto getU = [](uint64_t N) { return N >> 32; };
26 auto getL = [](uint64_t N) { return N & UINT32_MAX(4294967295U); };
27 uint64_t UL = getU(LHS), LL = getL(LHS), UR = getU(RHS), LR = getL(RHS);
28
29 // Compute cross products.
30 uint64_t P1 = UL * UR, P2 = UL * LR, P3 = LL * UR, P4 = LL * LR;
31
32 // Sum into two 64-bit digits.
33 uint64_t Upper = P1, Lower = P4;
34 auto addWithCarry = [&](uint64_t N) {
35 uint64_t NewLower = Lower + (getL(N) << 32);
36 Upper += getU(N) + (NewLower < Lower);
37 Lower = NewLower;
38 };
39 addWithCarry(P2);
40 addWithCarry(P3);
41
42 // Check whether the upper digit is empty.
43 if (!Upper)
44 return std::make_pair(Lower, 0);
45
46 // Shift as little as possible to maximize precision.
47 unsigned LeadingZeros = countLeadingZeros(Upper);
48 int Shift = 64 - LeadingZeros;
49 if (LeadingZeros)
50 Upper = Upper << LeadingZeros | Lower >> Shift;
51 return getRounded(Upper, Shift,
52 Shift && (Lower & UINT64_C(1)1UL << (Shift - 1)));
53}
54
55static uint64_t getHalf(uint64_t N) { return (N >> 1) + (N & 1); }
56
57std::pair<uint32_t, int16_t> ScaledNumbers::divide32(uint32_t Dividend,
58 uint32_t Divisor) {
59 assert(Dividend && "expected non-zero dividend")((Dividend && "expected non-zero dividend") ? static_cast
<void> (0) : __assert_fail ("Dividend && \"expected non-zero dividend\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 59, __PRETTY_FUNCTION__));
60 assert(Divisor && "expected non-zero divisor")((Divisor && "expected non-zero divisor") ? static_cast
<void> (0) : __assert_fail ("Divisor && \"expected non-zero divisor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 60, __PRETTY_FUNCTION__));
61
62 // Use 64-bit math and canonicalize the dividend to gain precision.
63 uint64_t Dividend64 = Dividend;
64 int Shift = 0;
65 if (int Zeros = countLeadingZeros(Dividend64)) {
66 Shift -= Zeros;
67 Dividend64 <<= Zeros;
68 }
69 uint64_t Quotient = Dividend64 / Divisor;
70 uint64_t Remainder = Dividend64 % Divisor;
71
72 // If Quotient needs to be shifted, leave the rounding to getAdjusted().
73 if (Quotient > UINT32_MAX(4294967295U))
74 return getAdjusted<uint32_t>(Quotient, Shift);
75
76 // Round based on the value of the next bit.
77 return getRounded<uint32_t>(Quotient, Shift, Remainder >= getHalf(Divisor));
78}
79
80std::pair<uint64_t, int16_t> ScaledNumbers::divide64(uint64_t Dividend,
81 uint64_t Divisor) {
82 assert(Dividend && "expected non-zero dividend")((Dividend && "expected non-zero dividend") ? static_cast
<void> (0) : __assert_fail ("Dividend && \"expected non-zero dividend\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 82, __PRETTY_FUNCTION__));
83 assert(Divisor && "expected non-zero divisor")((Divisor && "expected non-zero divisor") ? static_cast
<void> (0) : __assert_fail ("Divisor && \"expected non-zero divisor\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 83, __PRETTY_FUNCTION__));
84
85 // Minimize size of divisor.
86 int Shift = 0;
87 if (int Zeros = countTrailingZeros(Divisor)) {
88 Shift -= Zeros;
89 Divisor >>= Zeros;
90 }
91
92 // Check for powers of two.
93 if (Divisor == 1)
94 return std::make_pair(Dividend, Shift);
95
96 // Maximize size of dividend.
97 if (int Zeros = countLeadingZeros(Dividend)) {
98 Shift -= Zeros;
99 Dividend <<= Zeros;
100 }
101
102 // Start with the result of a divide.
103 uint64_t Quotient = Dividend / Divisor;
104 Dividend %= Divisor;
105
106 // Continue building the quotient with long division.
107 while (!(Quotient >> 63) && Dividend) {
108 // Shift Dividend and check for overflow.
109 bool IsOverflow = Dividend >> 63;
110 Dividend <<= 1;
111 --Shift;
112
113 // Get the next bit of Quotient.
114 Quotient <<= 1;
115 if (IsOverflow || Divisor <= Dividend) {
116 Quotient |= 1;
117 Dividend -= Divisor;
118 }
119 }
120
121 return getRounded(Quotient, Shift, Dividend >= getHalf(Divisor));
122}
123
124int ScaledNumbers::compareImpl(uint64_t L, uint64_t R, int ScaleDiff) {
125 assert(ScaleDiff >= 0 && "wrong argument order")((ScaleDiff >= 0 && "wrong argument order") ? static_cast
<void> (0) : __assert_fail ("ScaleDiff >= 0 && \"wrong argument order\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 125, __PRETTY_FUNCTION__));
126 assert(ScaleDiff < 64 && "numbers too far apart")((ScaleDiff < 64 && "numbers too far apart") ? static_cast
<void> (0) : __assert_fail ("ScaleDiff < 64 && \"numbers too far apart\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 126, __PRETTY_FUNCTION__));
127
128 uint64_t L_adjusted = L >> ScaleDiff;
129 if (L_adjusted < R)
130 return -1;
131 if (L_adjusted > R)
132 return 1;
133
134 return L > L_adjusted << ScaleDiff ? 1 : 0;
135}
136
137static void appendDigit(std::string &Str, unsigned D) {
138 assert(D < 10)((D < 10) ? static_cast<void> (0) : __assert_fail ("D < 10"
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 138, __PRETTY_FUNCTION__));
139 Str += '0' + D % 10;
140}
141
142static void appendNumber(std::string &Str, uint64_t N) {
143 while (N) {
144 appendDigit(Str, N % 10);
145 N /= 10;
146 }
147}
148
149static bool doesRoundUp(char Digit) {
150 switch (Digit) {
151 case '5':
152 case '6':
153 case '7':
154 case '8':
155 case '9':
156 return true;
157 default:
158 return false;
159 }
160}
161
162static std::string toStringAPFloat(uint64_t D, int E, unsigned Precision) {
163 assert(E >= ScaledNumbers::MinScale)((E >= ScaledNumbers::MinScale) ? static_cast<void> (
0) : __assert_fail ("E >= ScaledNumbers::MinScale", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 163, __PRETTY_FUNCTION__));
164 assert(E <= ScaledNumbers::MaxScale)((E <= ScaledNumbers::MaxScale) ? static_cast<void> (
0) : __assert_fail ("E <= ScaledNumbers::MaxScale", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 164, __PRETTY_FUNCTION__));
165
166 // Find a new E, but don't let it increase past MaxScale.
167 int LeadingZeros = ScaledNumberBase::countLeadingZeros64(D);
168 int NewE = std::min(ScaledNumbers::MaxScale, E + 63 - LeadingZeros);
169 int Shift = 63 - (NewE - E);
13
←
'Shift' initialized here
→
170 assert(Shift <= LeadingZeros)((Shift <= LeadingZeros) ? static_cast<void> (0) : __assert_fail
("Shift <= LeadingZeros", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 170, __PRETTY_FUNCTION__));
14
←
Within the expansion of the macro 'assert':
→
a
Assuming 'Shift' is <= 'LeadingZeros'
171 assert(Shift == LeadingZeros || NewE == ScaledNumbers::MaxScale)((Shift == LeadingZeros || NewE == ScaledNumbers::MaxScale) ?
static_cast<void> (0) : __assert_fail ("Shift == LeadingZeros || NewE == ScaledNumbers::MaxScale"
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 171, __PRETTY_FUNCTION__));
15
←
Within the expansion of the macro 'assert':
→
a
Assuming 'Shift' is equal to 'LeadingZeros'
172 D <<= Shift;
16
←
Assigned value is garbage or undefined
173 E = NewE;
174
175 // Check for a denormal.
176 unsigned AdjustedE = E + 16383;
177 if (!(D >> 63)) {
178 assert(E == ScaledNumbers::MaxScale)((E == ScaledNumbers::MaxScale) ? static_cast<void> (0)
: __assert_fail ("E == ScaledNumbers::MaxScale", "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 178, __PRETTY_FUNCTION__));
179 AdjustedE = 0;
180 }
181
182 // Build the float and print it.
183 uint64_t RawBits[2] = {D, AdjustedE};
184 APFloat Float(APFloat::x87DoubleExtended, APInt(80, RawBits));
185 SmallVector<char, 24> Chars;
186 Float.toString(Chars, Precision, 0);
187 return std::string(Chars.begin(), Chars.end());
188}
189
190static std::string stripTrailingZeros(const std::string &Float) {
191 size_t NonZero = Float.find_last_not_of('0');
192 assert(NonZero != std::string::npos && "no . in floating point string")((NonZero != std::string::npos && "no . in floating point string"
) ? static_cast<void> (0) : __assert_fail ("NonZero != std::string::npos && \"no . in floating point string\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.6~svn224007/lib/Support/ScaledNumber.cpp"
, 192, __PRETTY_FUNCTION__));
193
194 if (Float[NonZero] == '.')
195 ++NonZero;
196
197 return Float.substr(0, NonZero + 1);
198}
199
200std::string ScaledNumberBase::toString(uint64_t D, int16_t E, int Width,
201 unsigned Precision) {
202 if (!D)
1
Assuming 'D' is not equal to 0
→
2
←
Taking false branch
→
203 return "0.0";
204
205 // Canonicalize exponent and digits.
206 uint64_t Above0 = 0;
207 uint64_t Below0 = 0;
208 uint64_t Extra = 0;
209 int ExtraShift = 0;
210 if (E == 0) {
3
←
Assuming 'E' is not equal to 0
→
4
←
Taking false branch
→
211 Above0 = D;
212 } else if (E > 0) {
5
←
Assuming 'E' is > 0
→
6
←
Taking true branch
→
213 if (int Shift = std::min(int16_t(countLeadingZeros64(D)), E)) {
7
←
Assuming 'Shift' is not equal to 0
→
8
←
Taking true branch
→
214 D <<= Shift;
215 E -= Shift;
216
217 if (!E)
9
←
Assuming 'E' is not equal to 0
→
10
←
Taking false branch
→
218 Above0 = D;
219 }
220 } else if (E > -64) {
221 Above0 = D >> -E;
222 Below0 = D << (64 + E);
223 } else if (E == -64) {
224 // Special case: shift by 64 bits is undefined behavior.
225 Below0 = D;
226 } else if (E > -120) {
227 Below0 = D >> (-E - 64);
228 Extra = D << (128 + E);
229 ExtraShift = -64 - E;
230 }
231
232 // Fall back on APFloat for very small and very large numbers.
233 if (!Above0 && !Below0)
11
←
Taking true branch
→
234 return toStringAPFloat(D, E, Precision);
12
←
Calling 'toStringAPFloat'
→
235
236 // Append the digits before the decimal.
237 std::string Str;
238 size_t DigitsOut = 0;
239 if (Above0) {
240 appendNumber(Str, Above0);
241 DigitsOut = Str.size();
242 } else
243 appendDigit(Str, 0);
244 std::reverse(Str.begin(), Str.end());
245
246 // Return early if there's nothing after the decimal.
247 if (!Below0)
248 return Str + ".0";
249
250 // Append the decimal and beyond.
251 Str += '.';
252 uint64_t Error = UINT64_C(1)1UL << (64 - Width);
253
254 // We need to shift Below0 to the right to make space for calculating
255 // digits. Save the precision we're losing in Extra.
256 Extra = (Below0 & 0xf) << 56 | (Extra >> 8);
257 Below0 >>= 4;
258 size_t SinceDot = 0;
259 size_t AfterDot = Str.size();
260 do {
261 if (ExtraShift) {
262 --ExtraShift;
263 Error *= 5;
264 } else
265 Error *= 10;
266
267 Below0 *= 10;
268 Extra *= 10;
269 Below0 += (Extra >> 60);
270 Extra = Extra & (UINT64_MAX(18446744073709551615UL) >> 4);
271 appendDigit(Str, Below0 >> 60);
272 Below0 = Below0 & (UINT64_MAX(18446744073709551615UL) >> 4);
273 if (DigitsOut || Str.back() != '0')
274 ++DigitsOut;
275 ++SinceDot;
276 } while (Error && (Below0 << 4 | Extra >> 60) >= Error / 2 &&
277 (!Precision || DigitsOut <= Precision || SinceDot < 2));
278
279 // Return early for maximum precision.
280 if (!Precision || DigitsOut <= Precision)
281 return stripTrailingZeros(Str);
282
283 // Find where to truncate.
284 size_t Truncate =
285 std::max(Str.size() - (DigitsOut - Precision), AfterDot + 1);
286
287 // Check if there's anything to truncate.
288 if (Truncate >= Str.size())
289 return stripTrailingZeros(Str);
290
291 bool Carry = doesRoundUp(Str[Truncate]);
292 if (!Carry)
293 return stripTrailingZeros(Str.substr(0, Truncate));
294
295 // Round with the first truncated digit.
296 for (std::string::reverse_iterator I(Str.begin() + Truncate), E = Str.rend();
297 I != E; ++I) {
298 if (*I == '.')
299 continue;
300 if (*I == '9') {
301 *I = '0';
302 continue;
303 }
304
305 ++*I;
306 Carry = false;
307 break;
308 }
309
310 // Add "1" in front if we still need to carry.
311 return stripTrailingZeros(std::string(Carry, '1') + Str.substr(0, Truncate));
312}
313
314raw_ostream &ScaledNumberBase::print(raw_ostream &OS, uint64_t D, int16_t E,
315 int Width, unsigned Precision) {
316 return OS << toString(D, E, Width, Precision);
317}
318
319void ScaledNumberBase::dump(uint64_t D, int16_t E, int Width) {
320 print(dbgs(), D, E, Width, 0) << "[" << Width << ":" << D << "*2^" << E
321 << "]";
322}