1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements Branch Probability class.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Support/BranchProbability.h"
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Format.h"
17 #include "llvm/Support/raw_ostream.h"
22 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
23 auto GetHexDigit = [](int Val) -> char {
27 return 'a' + Val - 10;
30 for (int Digits = 0; Digits < 8; ++Digits)
31 OS << GetHexDigit(N >> (28 - Digits * 4) & 0xf);
33 for (int Digits = 0; Digits < 8; ++Digits)
34 OS << GetHexDigit(D >> (28 - Digits * 4) & 0xf);
35 OS << " = " << format("%.2f%%", ((double)N / D) * 100.0);
39 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
41 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
42 assert(Denominator > 0 && "Denominator cannot be 0!");
43 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
48 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
49 N = static_cast<uint32_t>(Prob64);
53 BranchProbability &BranchProbability::operator+=(BranchProbability RHS) {
54 assert(N <= D - RHS.N &&
55 "The sum of branch probabilities should not exceed one!");
60 BranchProbability &BranchProbability::operator-=(BranchProbability RHS) {
62 "Can only subtract a smaller probability from a larger one!");
67 // If ConstD is not zero, then replace D by ConstD so that division and modulo
68 // operations by D can be optimized, in case this function is not inlined by the
70 template <uint32_t ConstD>
71 inline uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
75 assert(D && "divide by 0");
77 // Fast path for multiplying by 1.0.
81 // Split Num into upper and lower parts to multiply, then recombine.
82 uint64_t ProductHigh = (Num >> 32) * N;
83 uint64_t ProductLow = (Num & UINT32_MAX) * N;
85 // Split into 32-bit digits.
86 uint32_t Upper32 = ProductHigh >> 32;
87 uint32_t Lower32 = ProductLow & UINT32_MAX;
88 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
89 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
92 Upper32 += Mid32 < Mid32Partial;
94 // Check for overflow.
98 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
99 uint64_t UpperQ = Rem / D;
101 // Check for overflow.
102 if (UpperQ > UINT32_MAX)
105 Rem = ((Rem % D) << 32) | Lower32;
106 uint64_t LowerQ = Rem / D;
107 uint64_t Q = (UpperQ << 32) + LowerQ;
109 // Check for overflow.
110 return Q < LowerQ ? UINT64_MAX : Q;
113 uint64_t BranchProbability::scale(uint64_t Num) const {
114 return ::scale<D>(Num, N, D);
117 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
118 return ::scale<0>(Num, D, N);