LCOV - code coverage report
Current view: top level - lib/Support - ScaledNumber.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 115 133 86.5 %
Date: 2018-06-17 00:07:59 Functions: 7 9 77.8 %
Legend: Lines: hit not hit

          Line data    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             : #include "llvm/ADT/APFloat.h"
      16             : #include "llvm/ADT/ArrayRef.h"
      17             : #include "llvm/Support/Debug.h"
      18             : #include "llvm/Support/raw_ostream.h"
      19             : 
      20             : using namespace llvm;
      21             : using namespace llvm::ScaledNumbers;
      22             : 
      23     1817433 : std::pair<uint64_t, int16_t> ScaledNumbers::multiply64(uint64_t LHS,
      24             :                                                        uint64_t RHS) {
      25             :   // Separate into two 32-bit digits (U.L).
      26     7269732 :   auto getU = [](uint64_t N) { return N >> 32; };
      27     3634866 :   auto getL = [](uint64_t N) { return N & UINT32_MAX; };
      28             :   uint64_t UL = getU(LHS), LL = getL(LHS), UR = getU(RHS), LR = getL(RHS);
      29             : 
      30             :   // Compute cross products.
      31     1817433 :   uint64_t P1 = UL * UR, P2 = UL * LR, P3 = LL * UR, P4 = LL * LR;
      32             : 
      33             :   // Sum into two 64-bit digits.
      34             :   uint64_t Upper = P1, Lower = P4;
      35             :   auto addWithCarry = [&](uint64_t N) {
      36     3634866 :     uint64_t NewLower = Lower + (getL(N) << 32);
      37     3634866 :     Upper += getU(N) + (NewLower < Lower);
      38     1817433 :     Lower = NewLower;
      39             :   };
      40             :   addWithCarry(P2);
      41             :   addWithCarry(P3);
      42             : 
      43             :   // Check whether the upper digit is empty.
      44     1817433 :   if (!Upper)
      45      336914 :     return std::make_pair(Lower, 0);
      46             : 
      47             :   // Shift as little as possible to maximize precision.
      48     1480519 :   unsigned LeadingZeros = countLeadingZeros(Upper);
      49     1480519 :   int Shift = 64 - LeadingZeros;
      50     1480519 :   if (LeadingZeros)
      51     1116452 :     Upper = Upper << LeadingZeros | Lower >> Shift;
      52             :   return getRounded(Upper, Shift,
      53     2251690 :                     Shift && (Lower & UINT64_C(1) << (Shift - 1)));
      54             : }
      55             : 
      56      172230 : static uint64_t getHalf(uint64_t N) { return (N >> 1) + (N & 1); }
      57             : 
      58          11 : std::pair<uint32_t, int16_t> ScaledNumbers::divide32(uint32_t Dividend,
      59             :                                                      uint32_t Divisor) {
      60             :   assert(Dividend && "expected non-zero dividend");
      61             :   assert(Divisor && "expected non-zero divisor");
      62             : 
      63             :   // Use 64-bit math and canonicalize the dividend to gain precision.
      64          11 :   uint64_t Dividend64 = Dividend;
      65             :   int Shift = 0;
      66          11 :   if (int Zeros = countLeadingZeros(Dividend64)) {
      67          11 :     Shift -= Zeros;
      68          11 :     Dividend64 <<= Zeros;
      69             :   }
      70          11 :   uint64_t Quotient = Dividend64 / Divisor;
      71          11 :   uint64_t Remainder = Dividend64 % Divisor;
      72             : 
      73             :   // If Quotient needs to be shifted, leave the rounding to getAdjusted().
      74          11 :   if (Quotient > UINT32_MAX)
      75          11 :     return getAdjusted<uint32_t>(Quotient, Shift);
      76             : 
      77             :   // Round based on the value of the next bit.
      78           0 :   return getRounded<uint32_t>(Quotient, Shift, Remainder >= getHalf(Divisor));
      79             : }
      80             : 
      81     2453705 : std::pair<uint64_t, int16_t> ScaledNumbers::divide64(uint64_t Dividend,
      82             :                                                      uint64_t Divisor) {
      83             :   assert(Dividend && "expected non-zero dividend");
      84             :   assert(Divisor && "expected non-zero divisor");
      85             : 
      86             :   // Minimize size of divisor.
      87             :   int Shift = 0;
      88     2453705 :   if (int Zeros = countTrailingZeros(Divisor)) {
      89      153600 :     Shift -= Zeros;
      90      153600 :     Divisor >>= Zeros;
      91             :   }
      92             : 
      93             :   // Check for powers of two.
      94     2453705 :   if (Divisor == 1)
      95     2281475 :     return std::make_pair(Dividend, Shift);
      96             : 
      97             :   // Maximize size of dividend.
      98      172230 :   if (int Zeros = countLeadingZeros(Dividend)) {
      99      155560 :     Shift -= Zeros;
     100      155560 :     Dividend <<= Zeros;
     101             :   }
     102             : 
     103             :   // Start with the result of a divide.
     104      172230 :   uint64_t Quotient = Dividend / Divisor;
     105      172230 :   Dividend %= Divisor;
     106             : 
     107             :   // Continue building the quotient with long division.
     108     6518310 :   while (!(Quotient >> 63) && Dividend) {
     109             :     // Shift Dividend and check for overflow.
     110     6346080 :     bool IsOverflow = Dividend >> 63;
     111     6346080 :     Dividend <<= 1;
     112     6346080 :     --Shift;
     113             : 
     114             :     // Get the next bit of Quotient.
     115     6346080 :     Quotient <<= 1;
     116     6346080 :     if (IsOverflow || Divisor <= Dividend) {
     117     3597612 :       Quotient |= 1;
     118     3597612 :       Dividend -= Divisor;
     119             :     }
     120             :   }
     121             : 
     122      172230 :   return getRounded(Quotient, Shift, Dividend >= getHalf(Divisor));
     123             : }
     124             : 
     125      284463 : int ScaledNumbers::compareImpl(uint64_t L, uint64_t R, int ScaleDiff) {
     126             :   assert(ScaleDiff >= 0 && "wrong argument order");
     127             :   assert(ScaleDiff < 64 && "numbers too far apart");
     128             : 
     129      284463 :   uint64_t L_adjusted = L >> ScaleDiff;
     130      284463 :   if (L_adjusted < R)
     131             :     return -1;
     132      193901 :   if (L_adjusted > R)
     133             :     return 1;
     134             : 
     135      125016 :   return L > L_adjusted << ScaleDiff ? 1 : 0;
     136             : }
     137             : 
     138             : static void appendDigit(std::string &Str, unsigned D) {
     139             :   assert(D < 10);
     140        3394 :   Str += '0' + D % 10;
     141             : }
     142             : 
     143             : static void appendNumber(std::string &Str, uint64_t N) {
     144        1088 :   while (N) {
     145         725 :     appendDigit(Str, N % 10);
     146         725 :     N /= 10;
     147             :   }
     148             : }
     149             : 
     150             : static bool doesRoundUp(char Digit) {
     151         388 :   switch (Digit) {
     152             :   case '5':
     153             :   case '6':
     154             :   case '7':
     155             :   case '8':
     156             :   case '9':
     157             :     return true;
     158             :   default:
     159             :     return false;
     160             :   }
     161             : }
     162             : 
     163           0 : static std::string toStringAPFloat(uint64_t D, int E, unsigned Precision) {
     164             :   assert(E >= ScaledNumbers::MinScale);
     165             :   assert(E <= ScaledNumbers::MaxScale);
     166             : 
     167             :   // Find a new E, but don't let it increase past MaxScale.
     168             :   int LeadingZeros = ScaledNumberBase::countLeadingZeros64(D);
     169           0 :   int NewE = std::min(ScaledNumbers::MaxScale, E + 63 - LeadingZeros);
     170           0 :   int Shift = 63 - (NewE - E);
     171             :   assert(Shift <= LeadingZeros);
     172             :   assert(Shift == LeadingZeros || NewE == ScaledNumbers::MaxScale);
     173             :   assert(Shift >= 0 && Shift < 64 && "undefined behavior");
     174           0 :   D <<= Shift;
     175             :   E = NewE;
     176             : 
     177             :   // Check for a denormal.
     178           0 :   unsigned AdjustedE = E + 16383;
     179           0 :   if (!(D >> 63)) {
     180             :     assert(E == ScaledNumbers::MaxScale);
     181             :     AdjustedE = 0;
     182             :   }
     183             : 
     184             :   // Build the float and print it.
     185           0 :   uint64_t RawBits[2] = {D, AdjustedE};
     186           0 :   APFloat Float(APFloat::x87DoubleExtended(), APInt(80, RawBits));
     187             :   SmallVector<char, 24> Chars;
     188           0 :   Float.toString(Chars, Precision, 0);
     189           0 :   return std::string(Chars.begin(), Chars.end());
     190             : }
     191             : 
     192         398 : static std::string stripTrailingZeros(const std::string &Float) {
     193         398 :   size_t NonZero = Float.find_last_not_of('0');
     194             :   assert(NonZero != std::string::npos && "no . in floating point string");
     195             : 
     196         398 :   if (Float[NonZero] == '.')
     197         150 :     ++NonZero;
     198             : 
     199         398 :   return Float.substr(0, NonZero + 1);
     200             : }
     201             : 
     202         532 : std::string ScaledNumberBase::toString(uint64_t D, int16_t E, int Width,
     203             :                                        unsigned Precision) {
     204         532 :   if (!D)
     205           0 :     return "0.0";
     206             : 
     207             :   // Canonicalize exponent and digits.
     208             :   uint64_t Above0 = 0;
     209             :   uint64_t Below0 = 0;
     210             :   uint64_t Extra = 0;
     211             :   int ExtraShift = 0;
     212         532 :   if (E == 0) {
     213             :     Above0 = D;
     214         402 :   } else if (E > 0) {
     215           4 :     if (int Shift = std::min(int16_t(countLeadingZeros64(D)), E)) {
     216           2 :       D <<= Shift;
     217           2 :       E -= Shift;
     218             : 
     219           2 :       if (!E)
     220             :         Above0 = D;
     221             :     }
     222         400 :   } else if (E > -64) {
     223         231 :     Above0 = D >> -E;
     224         231 :     Below0 = D << (64 + E);
     225         169 :   } else if (E == -64) {
     226             :     // Special case: shift by 64 bits is undefined behavior.
     227             :     Below0 = D;
     228          98 :   } else if (E > -120) {
     229          98 :     Below0 = D >> (-E - 64);
     230          98 :     Extra = D << (128 + E);
     231             :     ExtraShift = -64 - E;
     232             :   }
     233             : 
     234             :   // Fall back on APFloat for very small and very large numbers.
     235         532 :   if (!Above0 && !Below0)
     236           0 :     return toStringAPFloat(D, E, Precision);
     237             : 
     238             :   // Append the digits before the decimal.
     239             :   std::string Str;
     240             :   size_t DigitsOut = 0;
     241         532 :   if (Above0) {
     242             :     appendNumber(Str, Above0);
     243         363 :     DigitsOut = Str.size();
     244             :   } else
     245             :     appendDigit(Str, 0);
     246             :   std::reverse(Str.begin(), Str.end());
     247             : 
     248             :   // Return early if there's nothing after the decimal.
     249         532 :   if (!Below0)
     250         134 :     return Str + ".0";
     251             : 
     252             :   // Append the decimal and beyond.
     253             :   Str += '.';
     254         398 :   uint64_t Error = UINT64_C(1) << (64 - Width);
     255             : 
     256             :   // We need to shift Below0 to the right to make space for calculating
     257             :   // digits.  Save the precision we're losing in Extra.
     258         398 :   Extra = (Below0 & 0xf) << 56 | (Extra >> 8);
     259         398 :   Below0 >>= 4;
     260             :   size_t SinceDot = 0;
     261         398 :   size_t AfterDot = Str.size();
     262             :   do {
     263        2669 :     if (ExtraShift) {
     264        1258 :       --ExtraShift;
     265        1258 :       Error *= 5;
     266             :     } else
     267        1411 :       Error *= 10;
     268             : 
     269        2669 :     Below0 *= 10;
     270        2669 :     Extra *= 10;
     271        2669 :     Below0 += (Extra >> 60);
     272        2669 :     Extra = Extra & (UINT64_MAX >> 4);
     273        2669 :     appendDigit(Str, Below0 >> 60);
     274        2669 :     Below0 = Below0 & (UINT64_MAX >> 4);
     275        3663 :     if (DigitsOut || Str.back() != '0')
     276        1842 :       ++DigitsOut;
     277        2669 :     ++SinceDot;
     278        2669 :   } while (Error && (Below0 << 4 | Extra >> 60) >= Error / 2 &&
     279        2657 :            (!Precision || DigitsOut <= Precision || SinceDot < 2));
     280             : 
     281             :   // Return early for maximum precision.
     282         398 :   if (!Precision || DigitsOut <= Precision)
     283          10 :     return stripTrailingZeros(Str);
     284             : 
     285             :   // Find where to truncate.
     286             :   size_t Truncate =
     287         776 :       std::max(Str.size() - (DigitsOut - Precision), AfterDot + 1);
     288             : 
     289             :   // Check if there's anything to truncate.
     290         388 :   if (Truncate >= Str.size())
     291           0 :     return stripTrailingZeros(Str);
     292             : 
     293         388 :   bool Carry = doesRoundUp(Str[Truncate]);
     294             :   if (!Carry)
     295         262 :     return stripTrailingZeros(Str.substr(0, Truncate));
     296             : 
     297             :   // Round with the first truncated digit.
     298             :   for (std::string::reverse_iterator I(Str.begin() + Truncate), E = Str.rend();
     299         961 :        I != E; ++I) {
     300         953 :     if (*I == '.')
     301         114 :       continue;
     302        1429 :     if (*I == '9') {
     303         590 :       *I = '0';
     304         590 :       continue;
     305             :     }
     306             : 
     307         249 :     ++*I;
     308             :     Carry = false;
     309         249 :     break;
     310             :   }
     311             : 
     312             :   // Add "1" in front if we still need to carry.
     313        1285 :   return stripTrailingZeros(std::string(Carry, '1') + Str.substr(0, Truncate));
     314             : }
     315             : 
     316         532 : raw_ostream &ScaledNumberBase::print(raw_ostream &OS, uint64_t D, int16_t E,
     317             :                                      int Width, unsigned Precision) {
     318        1064 :   return OS << toString(D, E, Width, Precision);
     319             : }
     320             : 
     321           0 : void ScaledNumberBase::dump(uint64_t D, int16_t E, int Width) {
     322           0 :   print(dbgs(), D, E, Width, 0) << "[" << Width << ":" << D << "*2^" << E
     323           0 :                                 << "]";
     324           0 : }

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