1 //===- FixedPoint.h - Fixed point constant handling -------------*- 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 /// \file
11 /// Defines the fixed point number interface.
12 /// This is a class for abstracting various operations performed on fixed point
13 /// types described in ISO/IEC JTC1 SC22 WG14 N1169 starting at clause 4.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #ifndef LLVM_CLANG_BASIC_FIXEDPOINT_H
18 #define LLVM_CLANG_BASIC_FIXEDPOINT_H
19 
20 #include "llvm/ADT/APSInt.h"
21 
22 namespace clang {
23 
24 class ASTContext;
25 class QualType;
26 
27 /// The fixed point semantics work similarly to llvm::fltSemantics. The width
28 /// specifies the whole bit width of the underlying scaled integer (with padding
29 /// if any). The scale represents the number of fractional bits in this type.
30 /// When HasUnsignedPadding is true and this type is signed, the first bit
31 /// in the value this represents is treaded as padding.
32 class FixedPointSemantics {
33 public:
FixedPointSemantics(unsigned Width,unsigned Scale,bool IsSigned,bool IsSaturated,bool HasUnsignedPadding)34   FixedPointSemantics(unsigned Width, unsigned Scale, bool IsSigned,
35                       bool IsSaturated, bool HasUnsignedPadding)
36       : Width(Width), Scale(Scale), IsSigned(IsSigned),
37         IsSaturated(IsSaturated), HasUnsignedPadding(HasUnsignedPadding) {
38     assert(Width >= Scale && "Not enough room for the scale");
39   }
40 
getWidth()41   unsigned getWidth() const { return Width; }
getScale()42   unsigned getScale() const { return Scale; }
isSigned()43   bool isSigned() const { return IsSigned; }
isSaturated()44   bool isSaturated() const { return IsSaturated; }
hasUnsignedPadding()45   bool hasUnsignedPadding() const { return HasUnsignedPadding; }
46 
setSaturated(bool Saturated)47   void setSaturated(bool Saturated) { IsSaturated = Saturated; }
48 
getIntegralBits()49   unsigned getIntegralBits() const {
50     if (IsSigned || (!IsSigned && HasUnsignedPadding))
51       return Width - Scale - 1;
52     else
53       return Width - Scale;
54   }
55 
56 private:
57   unsigned Width;
58   unsigned Scale;
59   bool IsSigned;
60   bool IsSaturated;
61   bool HasUnsignedPadding;
62 };
63 
64 /// The APFixedPoint class works similarly to APInt/APSInt in that it is a
65 /// functional replacement for a scaled integer. It is meant to replicate the
66 /// fixed point types proposed in ISO/IEC JTC1 SC22 WG14 N1169. The class carries
67 /// info about the fixed point type's width, sign, scale, and saturation, and
68 /// provides different operations that would normally be performed on fixed point
69 /// types.
70 ///
71 /// Semantically this does not represent any existing C type other than fixed
72 /// point types and should eventually be moved to LLVM if fixed point types gain
73 /// native IR support.
74 class APFixedPoint {
75  public:
APFixedPoint(const llvm::APInt & Val,const FixedPointSemantics & Sema)76    APFixedPoint(const llvm::APInt &Val, const FixedPointSemantics &Sema)
77        : Val(Val, !Sema.isSigned()), Sema(Sema) {
78      assert(Val.getBitWidth() == Sema.getWidth() &&
79             "The value should have a bit width that matches the Sema width");
80    }
81 
APFixedPoint(uint64_t Val,const FixedPointSemantics & Sema)82    APFixedPoint(uint64_t Val, const FixedPointSemantics &Sema)
83        : APFixedPoint(llvm::APInt(Sema.getWidth(), Val, Sema.isSigned()),
84                       Sema) {}
85 
getValue()86    llvm::APSInt getValue() const { return llvm::APSInt(Val, !Sema.isSigned()); }
getWidth()87    inline unsigned getWidth() const { return Sema.getWidth(); }
getScale()88    inline unsigned getScale() const { return Sema.getScale(); }
isSaturated()89    inline bool isSaturated() const { return Sema.isSaturated(); }
isSigned()90    inline bool isSigned() const { return Sema.isSigned(); }
hasPadding()91    inline bool hasPadding() const { return Sema.hasUnsignedPadding(); }
92 
93    // Convert this number to match the semantics provided.
94    APFixedPoint convert(const FixedPointSemantics &DstSema) const;
95 
shr(unsigned Amt)96    APFixedPoint shr(unsigned Amt) const {
97      return APFixedPoint(Val >> Amt, Sema);
98   }
99 
shl(unsigned Amt)100   APFixedPoint shl(unsigned Amt) const {
101     return APFixedPoint(Val << Amt, Sema);
102   }
103 
getIntPart()104   llvm::APSInt getIntPart() const {
105     if (Val < 0 && Val != -Val) // Cover the case when we have the min val
106       return -(-Val >> getScale());
107     else
108       return Val >> getScale();
109   }
110 
111   // If LHS > RHS, return 1. If LHS == RHS, return 0. If LHS < RHS, return -1.
112   int compare(const APFixedPoint &Other) const;
113   bool operator==(const APFixedPoint &Other) const {
114     return compare(Other) == 0;
115   }
116   bool operator!=(const APFixedPoint &Other) const {
117     return compare(Other) != 0;
118   }
119   bool operator>(const APFixedPoint &Other) const { return compare(Other) > 0; }
120   bool operator<(const APFixedPoint &Other) const { return compare(Other) < 0; }
121   bool operator>=(const APFixedPoint &Other) const {
122     return compare(Other) >= 0;
123   }
124   bool operator<=(const APFixedPoint &Other) const {
125     return compare(Other) <= 0;
126   }
127 
128   static APFixedPoint getMax(const FixedPointSemantics &Sema);
129   static APFixedPoint getMin(const FixedPointSemantics &Sema);
130 
131 private:
132   llvm::APSInt Val;
133   FixedPointSemantics Sema;
134 };
135 
136 }  // namespace clang
137 
138 #endif
139