LLVM  3.7.0
BranchProbability.cpp
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1 //===-------------- lib/Support/BranchProbability.cpp -----------*- 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 // This file implements Branch Probability class.
11 //
12 //===----------------------------------------------------------------------===//
13 
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Format.h"
18 
19 using namespace llvm;
20 
22  return OS << N << " / " << D << " = "
23  << format("%g%%", ((double)N / D) * 100.0);
24 }
25 
26 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
27 
28 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
29  assert(D && "divide by 0");
30 
31  // Fast path for multiplying by 1.0.
32  if (!Num || D == N)
33  return Num;
34 
35  // Split Num into upper and lower parts to multiply, then recombine.
36  uint64_t ProductHigh = (Num >> 32) * N;
37  uint64_t ProductLow = (Num & UINT32_MAX) * N;
38 
39  // Split into 32-bit digits.
40  uint32_t Upper32 = ProductHigh >> 32;
41  uint32_t Lower32 = ProductLow & UINT32_MAX;
42  uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
43  uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
44 
45  // Carry.
46  Upper32 += Mid32 < Mid32Partial;
47 
48  // Check for overflow.
49  if (Upper32 >= D)
50  return UINT64_MAX;
51 
52  uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
53  uint64_t UpperQ = Rem / D;
54 
55  // Check for overflow.
56  if (UpperQ > UINT32_MAX)
57  return UINT64_MAX;
58 
59  Rem = ((Rem % D) << 32) | Lower32;
60  uint64_t LowerQ = Rem / D;
61  uint64_t Q = (UpperQ << 32) + LowerQ;
62 
63  // Check for overflow.
64  return Q < LowerQ ? UINT64_MAX : Q;
65 }
66 
67 uint64_t BranchProbability::scale(uint64_t Num) const {
68  return ::scale(Num, N, D);
69 }
70 
71 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
72  return ::scale(Num, D, N);
73 }
static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D)
format_object< Ts...> format(const char *Fmt, const Ts &...Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:111
uint64_t scaleByInverse(uint64_t Num) const
Scale a large integer by the inverse.
raw_ostream & print(raw_ostream &OS) const
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:123
uint64_t scale(uint64_t Num) const
Scale a large integer.
#define N
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:38