1// Copyright (c) 2015-2016 The Khronos Group Inc.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15#ifndef LIBSPIRV_UTIL_BITUTILS_H_
16#define LIBSPIRV_UTIL_BITUTILS_H_
17
18#include <cstdint>
19#include <cstring>
20
21namespace spvutils {
22
23// Performs a bitwise copy of source to the destination type Dest.
24template <typename Dest, typename Src>
25Dest BitwiseCast(Src source) {
26 Dest dest;
27 static_assert(sizeof(source) == sizeof(dest),
28 "BitwiseCast: Source and destination must have the same size");
29 std::memcpy(static_cast<void*>(&dest), &source, sizeof(dest));
30 return dest;
31}
32
33// SetBits<T, First, Num> returns an integer of type <T> with bits set
34// for position <First> through <First + Num - 1>, counting from the least
35// significant bit. In particular when Num == 0, no positions are set to 1.
36// A static assert will be triggered if First + Num > sizeof(T) * 8, that is,
37// a bit that will not fit in the underlying type is set.
38template <typename T, size_t First = 0, size_t Num = 0>
39struct SetBits {
40 static_assert(First < sizeof(T) * 8,
41 "Tried to set a bit that is shifted too far.");
42 const static T get = (T(1) << First) | SetBits<T, First + 1, Num - 1>::get;
43};
44
45template <typename T, size_t Last>
46struct SetBits<T, Last, 0> {
47 const static T get = T(0);
48};
49
50// This is all compile-time so we can put our tests right here.
51static_assert(SetBits<uint32_t, 0, 0>::get == uint32_t(0x00000000),
52 "SetBits failed");
53static_assert(SetBits<uint32_t, 0, 1>::get == uint32_t(0x00000001),
54 "SetBits failed");
55static_assert(SetBits<uint32_t, 31, 1>::get == uint32_t(0x80000000),
56 "SetBits failed");
57static_assert(SetBits<uint32_t, 1, 2>::get == uint32_t(0x00000006),
58 "SetBits failed");
59static_assert(SetBits<uint32_t, 30, 2>::get == uint32_t(0xc0000000),
60 "SetBits failed");
61static_assert(SetBits<uint32_t, 0, 31>::get == uint32_t(0x7FFFFFFF),
62 "SetBits failed");
63static_assert(SetBits<uint32_t, 0, 32>::get == uint32_t(0xFFFFFFFF),
64 "SetBits failed");
65static_assert(SetBits<uint32_t, 16, 16>::get == uint32_t(0xFFFF0000),
66 "SetBits failed");
67
68static_assert(SetBits<uint64_t, 0, 1>::get == uint64_t(0x0000000000000001LL),
69 "SetBits failed");
70static_assert(SetBits<uint64_t, 63, 1>::get == uint64_t(0x8000000000000000LL),
71 "SetBits failed");
72static_assert(SetBits<uint64_t, 62, 2>::get == uint64_t(0xc000000000000000LL),
73 "SetBits failed");
74static_assert(SetBits<uint64_t, 31, 1>::get == uint64_t(0x0000000080000000LL),
75 "SetBits failed");
76static_assert(SetBits<uint64_t, 16, 16>::get == uint64_t(0x00000000FFFF0000LL),
77 "SetBits failed");
78
79} // namespace spvutils
80
81#endif // LIBSPIRV_UTIL_BITUTILS_H_
82