openMSX
endian.hh
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1#ifndef ENDIAN_HH
2#define ENDIAN_HH
3
4#include "inline.hh"
5#include <bit>
6#include <cassert>
7#include <concepts>
8#include <cstdint>
9#include <cstring>
10
11namespace Endian {
12
13inline constexpr bool BIG = std::endian::native == std::endian::big;
14inline constexpr bool LITTLE = std::endian::native == std::endian::little;
15static_assert(BIG || LITTLE, "mixed endian not supported");
16
17// Reverse bytes in a 16-bit number: 0x1234 becomes 0x3412
18[[nodiscard]] static inline uint16_t byteswap16(uint16_t x)
19{
20 // This sequence generates 'optimal' code on a wide range of gcc/clang
21 // versions (a single rotate instruction on x86). The newer compiler
22 // versions also do 'the right thing' for the simpler expression below.
23 // Those newer compilers also support __builtin_bswap16() but that
24 // doesn't generate better code (and is less portable).
25 return ((x & 0x00FF) << 8) | ((x & 0xFF00) >> 8);
26 //return (x << 8) | (x >> 8);
27}
28
29// Reverse bytes in a 32-bit number: 0x12345678 becomes 0x78563412
30[[nodiscard]] static inline uint32_t byteswap32(uint32_t x)
31{
32#if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 3))
33 // Starting from gcc-4.3 there's a builtin function for this.
34 // E.g. on x86 this is translated to a single 'bswap' instruction.
35 return __builtin_bswap32(x);
36#else
37 return (x << 24) |
38 ((x << 8) & 0x00ff0000) |
39 ((x >> 8) & 0x0000ff00) |
40 (x >> 24);
41#endif
42}
43
44// Reverse bytes in a 64-bit value: 0x1122334455667788 becomes 0x8877665544332211
45[[nodiscard]] static inline uint64_t byteswap64(uint64_t x)
46{
47#if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 3))
48 // Starting from gcc-4.3 there's a builtin function for this.
49 // E.g. on x86 this is translated to a single 'bswap' instruction.
50 return __builtin_bswap64(x);
51#else
52 return (uint64_t(byteswap32(x >> 0)) << 32) |
53 (uint64_t(byteswap32(x >> 32)) << 0);
54#endif
55}
56
57// Use overloading to get a (statically) polymorphic byteswap() function.
58[[nodiscard]] static inline uint16_t byteswap(uint16_t x) { return byteswap16(x); }
59[[nodiscard]] static inline uint32_t byteswap(uint32_t x) { return byteswap32(x); }
60[[nodiscard]] static inline uint64_t byteswap(uint64_t x) { return byteswap64(x); }
61
62
63// Identity operator, simply returns the given value.
64struct Ident {
65 [[nodiscard]] inline auto operator()(std::integral auto t) const { return t; }
66};
67
68// Byte-swap operator, swap bytes in the given value (16 or 32 bit).
69struct ByteSwap {
70 [[nodiscard]] inline auto operator()(std::integral auto t) const { return byteswap(t); }
71};
72
73// Helper class that stores a value and allows to read/write that value. Though
74// right before it is loaded/stored the value is transformed by a configurable
75// operation.
76// TODO If needed this can be extended with stuff like operator+= ....
77template<std::integral T, std::invocable<T> Op> class EndianT {
78public:
79 EndianT() = default; // leave uninitialized
80 EndianT(T t_) { Op op; t = op(t_); }
81 [[nodiscard]] inline operator T() const { Op op; return op(t); }
82 inline EndianT& operator=(T a) { Op op; t = op(a); return *this; }
83private:
84 T t;
85};
86
87// Define the types B16, B32, L16, L32.
88//
89// Typically these types are used to define the layout of external structures
90// For example:
91//
92// struct FATDirectoryEntry {
93// char filename[8];
94// char extension[3];
95// ...
96// Endian::L32 size; // 32-bit little endian value
97// };
98// ...
99// unsigned s = myDirEntry.size; // Possibly performs endianess conversion.
100// yourDirEntry.size = s; // If native endianess is already correct
101// // this has no extra overhead.
102//
103// You can assign and read values in native endianess to values of these types.
104// So basically in a single location define the structure with the correct
105// endianess and in all other places use the value as-if it were a native type.
106//
107// Note that these types should still be correctly aligned (e.g. L32 should be
108// 4-byte aligned). For unaligned access use the functions below.
109//
110template<bool> struct ConvBig;
111template<> struct ConvBig <true > : Ident {};
112template<> struct ConvBig <false> : ByteSwap {};
113template<bool> struct ConvLittle;
114template<> struct ConvLittle<true > : ByteSwap {};
115template<> struct ConvLittle<false> : Ident {};
122static_assert(sizeof(B16) == 2, "must have size 2");
123static_assert(sizeof(L16) == 2, "must have size 2");
124static_assert(sizeof(B32) == 4, "must have size 4");
125static_assert(sizeof(L32) == 4, "must have size 4");
126static_assert(sizeof(B64) == 8, "must have size 8");
127static_assert(sizeof(L64) == 8, "must have size 8");
128static_assert(alignof(B16) <= 2, "may have alignment 2");
129static_assert(alignof(L16) <= 2, "may have alignment 2");
130static_assert(alignof(B32) <= 4, "may have alignment 4");
131static_assert(alignof(L32) <= 4, "may have alignment 4");
132static_assert(alignof(B64) <= 8, "may have alignment 8");
133static_assert(alignof(L64) <= 8, "may have alignment 8");
134
135
136// Helper functions to read/write aligned 16/32 bit values.
137inline void writeB16(void* p, uint16_t x)
138{
139 *reinterpret_cast<B16*>(p) = x;
140}
141inline void writeL16(void* p, uint16_t x)
142{
143 *reinterpret_cast<L16*>(p) = x;
144}
145inline void writeB32(void* p, uint32_t x)
146{
147 *reinterpret_cast<B32*>(p) = x;
148}
149inline void writeL32(void* p, uint32_t x)
150{
151 *reinterpret_cast<L32*>(p) = x;
152}
153
154[[nodiscard]] inline uint16_t readB16(const void* p)
155{
156 return *reinterpret_cast<const B16*>(p);
157}
158[[nodiscard]] inline uint16_t readL16(const void* p)
159{
160 return *reinterpret_cast<const L16*>(p);
161}
162[[nodiscard]] inline uint32_t readB32(const void* p)
163{
164 return *reinterpret_cast<const B32*>(p);
165}
166[[nodiscard]] inline uint32_t readL32(const void* p)
167{
168 return *reinterpret_cast<const L32*>(p);
169}
170
171// Read/write big/little 16/24/32/64-bit values to/from a (possibly) unaligned
172// memory location. If the host architecture supports unaligned load/stores
173// (e.g. x86), these functions perform a single load/store (with possibly an
174// adjust operation on the value if the endianess is different from the host
175// endianess). If the architecture does not support unaligned memory operations
176// (e.g. early ARM architectures), the operation is split into byte accesses.
177
178template<bool SWAP> static ALWAYS_INLINE void write_UA(void* p, std::integral auto x)
179{
180 if constexpr (SWAP) x = byteswap(x);
181 memcpy(p, &x, sizeof(x));
182}
183ALWAYS_INLINE void write_UA_B16(void* p, uint16_t x)
184{
185 write_UA<LITTLE>(p, x);
186}
187ALWAYS_INLINE void write_UA_L16(void* p, uint16_t x)
188{
189 write_UA<BIG>(p, x);
190}
191ALWAYS_INLINE void write_UA_L24(void* p, uint32_t x)
192{
193 assert(x < 0x1000000);
194 auto* v = static_cast<uint8_t*>(p);
195 v[0] = (x >> 0) & 0xff;
196 v[1] = (x >> 8) & 0xff;
197 v[2] = (x >> 16) & 0xff;
198}
199ALWAYS_INLINE void write_UA_B32(void* p, uint32_t x)
200{
201 write_UA<LITTLE>(p, x);
202}
203ALWAYS_INLINE void write_UA_L32(void* p, uint32_t x)
204{
205 write_UA<BIG>(p, x);
206}
207ALWAYS_INLINE void write_UA_B64(void* p, uint64_t x)
208{
209 write_UA<LITTLE>(p, x);
210}
211ALWAYS_INLINE void write_UA_L64(void* p, uint64_t x)
212{
213 write_UA<BIG>(p, x);
214}
215
216template<bool SWAP, std::integral T> [[nodiscard]] static ALWAYS_INLINE T read_UA(const void* p)
217{
218 T x;
219 memcpy(&x, p, sizeof(x));
220 if constexpr (SWAP) x = byteswap(x);
221 return x;
222}
223[[nodiscard]] ALWAYS_INLINE uint16_t read_UA_B16(const void* p)
224{
225 return read_UA<LITTLE, uint16_t>(p);
226}
227[[nodiscard]] ALWAYS_INLINE uint16_t read_UA_L16(const void* p)
228{
229 return read_UA<BIG, uint16_t>(p);
230}
231[[nodiscard]] ALWAYS_INLINE uint32_t read_UA_L24(const void* p)
232{
233 const auto* v = static_cast<const uint8_t*>(p);
234 return (v[0] << 0) | (v[1] << 8) | (v[2] << 16);
235}
236[[nodiscard]] ALWAYS_INLINE uint32_t read_UA_B32(const void* p)
237{
238 return read_UA<LITTLE, uint32_t>(p);
239}
240[[nodiscard]] ALWAYS_INLINE uint32_t read_UA_L32(const void* p)
241{
242 return read_UA<BIG, uint32_t>(p);
243}
244[[nodiscard]] ALWAYS_INLINE uint64_t read_UA_B64(const void* p)
245{
246 return read_UA<LITTLE, uint64_t>(p);
247}
248[[nodiscard]] ALWAYS_INLINE uint64_t read_UA_L64(const void* p)
249{
250 return read_UA<BIG, uint64_t>(p);
251}
252
253
254// Like the types above, but these don't need to be aligned.
255
256class UA_B16 {
257public:
258 [[nodiscard]] inline operator uint16_t() const { return read_UA_B16(x); }
259 inline UA_B16& operator=(uint16_t a) { write_UA_B16(x, a); return *this; }
260private:
261 uint8_t x[2];
262};
263
264class UA_L16 {
265public:
266 [[nodiscard]] inline operator uint16_t() const { return read_UA_L16(x); }
267 inline UA_L16& operator=(uint16_t a) { write_UA_L16(x, a); return *this; }
268private:
269 uint8_t x[2];
270};
271
272class UA_L24 {
273public:
274 inline operator uint32_t() const { return read_UA_L24(x); }
275 inline UA_L24& operator=(uint32_t a) { write_UA_L24(x, a); return *this; }
276private:
277 uint8_t x[3];
278};
279
280class UA_B32 {
281public:
282 [[nodiscard]] inline operator uint32_t() const { return read_UA_B32(x); }
283 inline UA_B32& operator=(uint32_t a) { write_UA_B32(x, a); return *this; }
284private:
285 uint8_t x[4];
286};
287
288class UA_L32 {
289public:
290 [[nodiscard]] inline operator uint32_t() const { return read_UA_L32(x); }
291 inline UA_L32& operator=(uint32_t a) { write_UA_L32(x, a); return *this; }
292private:
293 uint8_t x[4];
294};
295
296static_assert(sizeof(UA_B16) == 2, "must have size 2");
297static_assert(sizeof(UA_L16) == 2, "must have size 2");
298static_assert(sizeof(UA_L24) == 3, "must have size 3");
299static_assert(sizeof(UA_B32) == 4, "must have size 4");
300static_assert(sizeof(UA_L32) == 4, "must have size 4");
301static_assert(alignof(UA_B16) == 1, "must have alignment 1");
302static_assert(alignof(UA_L16) == 1, "must have alignment 1");
303static_assert(alignof(UA_L24) == 1, "must have alignment 1");
304static_assert(alignof(UA_B32) == 1, "must have alignment 1");
305static_assert(alignof(UA_L32) == 1, "must have alignment 1");
306
307// Template meta-programming.
308// Get a type of the same size of the given type that stores the value in a
309// specific endianess. Typically used in template functions that can work on
310// either 16 or 32 bit values.
311// usage:
312// using LE_T = typename Endian::Little<T>::type;
313// The type LE_T is now a type that stores values of the same size as 'T'
314// in little endian format (independent of host endianess).
315template<typename> struct Little;
316template<> struct Little<uint8_t > { using type = uint8_t; };
317template<> struct Little<uint16_t> { using type = L16; };
318template<> struct Little<uint32_t> { using type = L32; };
319template<typename> struct Big;
320template<> struct Big<uint8_t > { using type = uint8_t; };
321template<> struct Big<uint16_t> { using type = B16; };
322template<> struct Big<uint32_t> { using type = B32; };
323
324} // namespace Endian
325
326#endif
TclObject t
EndianT(T t_)
Definition: endian.hh:80
EndianT & operator=(T a)
Definition: endian.hh:82
EndianT()=default
UA_B16 & operator=(uint16_t a)
Definition: endian.hh:259
UA_B32 & operator=(uint32_t a)
Definition: endian.hh:283
UA_L16 & operator=(uint16_t a)
Definition: endian.hh:267
UA_L24 & operator=(uint32_t a)
Definition: endian.hh:275
UA_L32 & operator=(uint32_t a)
Definition: endian.hh:291
#define ALWAYS_INLINE
Definition: inline.hh:16
Definition: endian.hh:11
uint16_t readB16(const void *p)
Definition: endian.hh:154
ALWAYS_INLINE uint32_t read_UA_L24(const void *p)
Definition: endian.hh:231
ALWAYS_INLINE uint16_t read_UA_B16(const void *p)
Definition: endian.hh:223
void writeB16(void *p, uint16_t x)
Definition: endian.hh:137
ALWAYS_INLINE void write_UA_B32(void *p, uint32_t x)
Definition: endian.hh:199
ALWAYS_INLINE void write_UA_B64(void *p, uint64_t x)
Definition: endian.hh:207
uint32_t readL32(const void *p)
Definition: endian.hh:166
ALWAYS_INLINE void write_UA_L24(void *p, uint32_t x)
Definition: endian.hh:191
ALWAYS_INLINE void write_UA_B16(void *p, uint16_t x)
Definition: endian.hh:183
void writeL32(void *p, uint32_t x)
Definition: endian.hh:149
ALWAYS_INLINE uint64_t read_UA_L64(const void *p)
Definition: endian.hh:248
ALWAYS_INLINE uint32_t read_UA_B32(const void *p)
Definition: endian.hh:236
void writeB32(void *p, uint32_t x)
Definition: endian.hh:145
ALWAYS_INLINE void write_UA_L64(void *p, uint64_t x)
Definition: endian.hh:211
constexpr bool LITTLE
Definition: endian.hh:14
ALWAYS_INLINE uint16_t read_UA_L16(const void *p)
Definition: endian.hh:227
ALWAYS_INLINE uint64_t read_UA_B64(const void *p)
Definition: endian.hh:244
EndianT< uint16_t, ConvBig< BIG > > B16
Definition: endian.hh:116
ALWAYS_INLINE void write_UA_L32(void *p, uint32_t x)
Definition: endian.hh:203
EndianT< uint32_t, ConvBig< BIG > > B32
Definition: endian.hh:118
ALWAYS_INLINE void write_UA_L16(void *p, uint16_t x)
Definition: endian.hh:187
EndianT< uint32_t, ConvLittle< BIG > > L32
Definition: endian.hh:119
uint16_t readL16(const void *p)
Definition: endian.hh:158
uint32_t readB32(const void *p)
Definition: endian.hh:162
EndianT< uint16_t, ConvLittle< BIG > > L16
Definition: endian.hh:117
EndianT< uint64_t, ConvBig< BIG > > B64
Definition: endian.hh:120
constexpr bool BIG
Definition: endian.hh:13
ALWAYS_INLINE uint32_t read_UA_L32(const void *p)
Definition: endian.hh:240
EndianT< uint64_t, ConvLittle< BIG > > L64
Definition: endian.hh:121
void writeL16(void *p, uint16_t x)
Definition: endian.hh:141
constexpr KeyMatrixPosition x
Keyboard bindings.
Definition: Keyboard.cc:127
auto operator()(std::integral auto t) const
Definition: endian.hh:70
auto operator()(std::integral auto t) const
Definition: endian.hh:65