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 const uint32_t BranchProbability::D;
24 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
25 // Get a percentage rounded to two decimal digits. This avoids
26 // implementation-defined rounding inside printf.
27 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
28 OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D, Percent);
32 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
34 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
35 assert(Denominator > 0 && "Denominator cannot be 0!");
36 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
41 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
42 N = static_cast<uint32_t>(Prob64);
46 // If ConstD is not zero, then replace D by ConstD so that division and modulo
47 // operations by D can be optimized, in case this function is not inlined by the
49 template <uint32_t ConstD>
50 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
54 assert(D && "divide by 0");
56 // Fast path for multiplying by 1.0.
60 // Split Num into upper and lower parts to multiply, then recombine.
61 uint64_t ProductHigh = (Num >> 32) * N;
62 uint64_t ProductLow = (Num & UINT32_MAX) * N;
64 // Split into 32-bit digits.
65 uint32_t Upper32 = ProductHigh >> 32;
66 uint32_t Lower32 = ProductLow & UINT32_MAX;
67 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
68 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
71 Upper32 += Mid32 < Mid32Partial;
73 // Check for overflow.
77 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
78 uint64_t UpperQ = Rem / D;
80 // Check for overflow.
81 if (UpperQ > UINT32_MAX)
84 Rem = ((Rem % D) << 32) | Lower32;
85 uint64_t LowerQ = Rem / D;
86 uint64_t Q = (UpperQ << 32) + LowerQ;
88 // Check for overflow.
89 return Q < LowerQ ? UINT64_MAX : Q;
92 uint64_t BranchProbability::scale(uint64_t Num) const {
93 return ::scale<D>(Num, N, D);
96 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
97 return ::scale<0>(Num, D, N);