1//===- FixedPoint.h - Fixed point constant handling -------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9/// \file
10/// Defines the fixed point number interface.
11/// This is a class for abstracting various operations performed on fixed point
12/// types described in ISO/IEC JTC1 SC22 WG14 N1169 starting at clause 4.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_CLANG_BASIC_FIXEDPOINT_H
17#define LLVM_CLANG_BASIC_FIXEDPOINT_H
18
19#include "llvm/ADT/APSInt.h"
20#include "llvm/ADT/SmallString.h"
21#include "llvm/Support/raw_ostream.h"
22
23namespace clang {
24
25class ASTContext;
26class QualType;
27
28/// The fixed point semantics work similarly to llvm::fltSemantics. The width
29/// specifies the whole bit width of the underlying scaled integer (with padding
30/// if any). The scale represents the number of fractional bits in this type.
31/// When HasUnsignedPadding is true and this type is signed, the first bit
32/// in the value this represents is treaded as padding.
33class FixedPointSemantics {
34public:
35 FixedPointSemantics(unsigned Width, unsigned Scale, bool IsSigned,
36 bool IsSaturated, bool HasUnsignedPadding)
37 : Width(Width), Scale(Scale), IsSigned(IsSigned),
38 IsSaturated(IsSaturated), HasUnsignedPadding(HasUnsignedPadding) {
39 assert(Width >= Scale && "Not enough room for the scale");
40 assert(!(IsSigned && HasUnsignedPadding) &&
41 "Cannot have unsigned padding on a signed type.");
42 }
43
44 unsigned getWidth() const { return Width; }
45 unsigned getScale() const { return Scale; }
46 bool isSigned() const { return IsSigned; }
47 bool isSaturated() const { return IsSaturated; }
48 bool hasUnsignedPadding() const { return HasUnsignedPadding; }
49
50 void setSaturated(bool Saturated) { IsSaturated = Saturated; }
51
52 /// Return the number of integral bits represented by these semantics. These
53 /// are separate from the fractional bits and do not include the sign or
54 /// padding bit.
55 unsigned getIntegralBits() const {
56 if (IsSigned || (!IsSigned && HasUnsignedPadding))
57 return Width - Scale - 1;
58 else
59 return Width - Scale;
60 }
61
62 /// Return the FixedPointSemantics that allows for calculating the full
63 /// precision semantic that can precisely represent the precision and ranges
64 /// of both input values. This does not compute the resulting semantics for a
65 /// given binary operation.
66 FixedPointSemantics
67 getCommonSemantics(const FixedPointSemantics &Other) const;
68
69 /// Return the FixedPointSemantics for an integer type.
70 static FixedPointSemantics GetIntegerSemantics(unsigned Width,
71 bool IsSigned) {
72 return FixedPointSemantics(Width, /*Scale=*/0, IsSigned,
73 /*IsSaturated=*/false,
74 /*HasUnsignedPadding=*/false);
75 }
76
77private:
78 unsigned Width;
79 unsigned Scale;
80 bool IsSigned;
81 bool IsSaturated;
82 bool HasUnsignedPadding;
83};
84
85/// The APFixedPoint class works similarly to APInt/APSInt in that it is a
86/// functional replacement for a scaled integer. It is meant to replicate the
87/// fixed point types proposed in ISO/IEC JTC1 SC22 WG14 N1169. The class carries
88/// info about the fixed point type's width, sign, scale, and saturation, and
89/// provides different operations that would normally be performed on fixed point
90/// types.
91///
92/// Semantically this does not represent any existing C type other than fixed
93/// point types and should eventually be moved to LLVM if fixed point types gain
94/// native IR support.
95class APFixedPoint {
96 public:
97 APFixedPoint(const llvm::APInt &Val, const FixedPointSemantics &Sema)
98 : Val(Val, !Sema.isSigned()), Sema(Sema) {
99 assert(Val.getBitWidth() == Sema.getWidth() &&
100 "The value should have a bit width that matches the Sema width");
101 }
102
103 APFixedPoint(uint64_t Val, const FixedPointSemantics &Sema)
104 : APFixedPoint(llvm::APInt(Sema.getWidth(), Val, Sema.isSigned()),
105 Sema) {}
106
107 // Zero initialization.
108 APFixedPoint(const FixedPointSemantics &Sema) : APFixedPoint(0, Sema) {}
109
110 llvm::APSInt getValue() const { return llvm::APSInt(Val, !Sema.isSigned()); }
111 inline unsigned getWidth() const { return Sema.getWidth(); }
112 inline unsigned getScale() const { return Sema.getScale(); }
113 inline bool isSaturated() const { return Sema.isSaturated(); }
114 inline bool isSigned() const { return Sema.isSigned(); }
115 inline bool hasPadding() const { return Sema.hasUnsignedPadding(); }
116 FixedPointSemantics getSemantics() const { return Sema; }
117
118 bool getBoolValue() const { return Val.getBoolValue(); }
119
120 // Convert this number to match the semantics provided. If the overflow
121 // parameter is provided, set this value to true or false to indicate if this
122 // operation results in an overflow.
123 APFixedPoint convert(const FixedPointSemantics &DstSema,
124 bool *Overflow = nullptr) const;
125
126 // Perform binary operations on a fixed point type. The resulting fixed point
127 // value will be in the common, full precision semantics that can represent
128 // the precision and ranges os both input values. See convert() for an
129 // explanation of the Overflow parameter.
130 APFixedPoint add(const APFixedPoint &Other, bool *Overflow = nullptr) const;
131
132 /// Perform a unary negation (-X) on this fixed point type, taking into
133 /// account saturation if applicable.
134 APFixedPoint negate(bool *Overflow = nullptr) const;
135
136 APFixedPoint shr(unsigned Amt) const {
137 return APFixedPoint(Val >> Amt, Sema);
138 }
139
140 APFixedPoint shl(unsigned Amt) const {
141 return APFixedPoint(Val << Amt, Sema);
142 }
143
144 llvm::APSInt getIntPart() const {
145 if (Val < 0 && Val != -Val) // Cover the case when we have the min val
146 return -(-Val >> getScale());
147 else
148 return Val >> getScale();
149 }
150
151 void toString(llvm::SmallVectorImpl<char> &Str) const;
152 std::string toString() const {
153 llvm::SmallString<40> S;
154 toString(S);
155 return S.str();
156 }
157
158 // If LHS > RHS, return 1. If LHS == RHS, return 0. If LHS < RHS, return -1.
159 int compare(const APFixedPoint &Other) const;
160 bool operator==(const APFixedPoint &Other) const {
161 return compare(Other) == 0;
162 }
163 bool operator!=(const APFixedPoint &Other) const {
164 return compare(Other) != 0;
165 }
166 bool operator>(const APFixedPoint &Other) const { return compare(Other) > 0; }
167 bool operator<(const APFixedPoint &Other) const { return compare(Other) < 0; }
168 bool operator>=(const APFixedPoint &Other) const {
169 return compare(Other) >= 0;
170 }
171 bool operator<=(const APFixedPoint &Other) const {
172 return compare(Other) <= 0;
173 }
174
175 static APFixedPoint getMax(const FixedPointSemantics &Sema);
176 static APFixedPoint getMin(const FixedPointSemantics &Sema);
177
178private:
179 llvm::APSInt Val;
180 FixedPointSemantics Sema;
181};
182
183inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
184 const APFixedPoint &FX) {
185 OS << FX.toString();
186 return OS;
187}
188
189} // namespace clang
190
191#endif
192