1 //===- Endian.h - Utilities for IO with endian specific data ----*- 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 // This file declares generic functions to read and write endian specific data.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_SUPPORT_ENDIAN_H
14 #define LLVM_SUPPORT_ENDIAN_H
15 
16 #include "llvm/Support/Compiler.h"
17 #include "llvm/Support/SwapByteOrder.h"
18 #include <cassert>
19 #include <cstddef>
20 #include <cstdint>
21 #include <cstring>
22 #include <type_traits>
23 
24 namespace llvm {
25 namespace support {
26 
27 enum endianness {big, little, native};
28 
29 // These are named values for common alignments.
30 enum {aligned = 0, unaligned = 1};
31 
32 namespace detail {
33 
34 /// ::value is either alignment, or alignof(T) if alignment is 0.
35 template<class T, int alignment>
36 struct PickAlignment {
37  enum { value = alignment == 0 ? alignof(T) : alignment };
38 };
39 
40 } // end namespace detail
41 
42 namespace endian {
43 
system_endianness()44 constexpr endianness system_endianness() {
45   return sys::IsBigEndianHost ? big : little;
46 }
47 
48 template <typename value_type>
byte_swap(value_type value,endianness endian)49 inline value_type byte_swap(value_type value, endianness endian) {
50   if ((endian != native) && (endian != system_endianness()))
51     sys::swapByteOrder(value);
52   return value;
53 }
54 
55 /// Swap the bytes of value to match the given endianness.
56 template<typename value_type, endianness endian>
byte_swap(value_type value)57 inline value_type byte_swap(value_type value) {
58   return byte_swap(value, endian);
59 }
60 
61 /// Read a value of a particular endianness from memory.
62 template <typename value_type, std::size_t alignment>
read(const void * memory,endianness endian)63 inline value_type read(const void *memory, endianness endian) {
64   value_type ret;
65 
66   memcpy(&ret,
67          LLVM_ASSUME_ALIGNED(
68              memory, (detail::PickAlignment<value_type, alignment>::value)),
69          sizeof(value_type));
70   return byte_swap<value_type>(ret, endian);
71 }
72 
73 template<typename value_type,
74          endianness endian,
75          std::size_t alignment>
read(const void * memory)76 inline value_type read(const void *memory) {
77   return read<value_type, alignment>(memory, endian);
78 }
79 
80 /// Read a value of a particular endianness from a buffer, and increment the
81 /// buffer past that value.
82 template <typename value_type, std::size_t alignment, typename CharT>
readNext(const CharT * & memory,endianness endian)83 inline value_type readNext(const CharT *&memory, endianness endian) {
84   value_type ret = read<value_type, alignment>(memory, endian);
85   memory += sizeof(value_type);
86   return ret;
87 }
88 
89 template<typename value_type, endianness endian, std::size_t alignment,
90          typename CharT>
readNext(const CharT * & memory)91 inline value_type readNext(const CharT *&memory) {
92   return readNext<value_type, alignment, CharT>(memory, endian);
93 }
94 
95 /// Write a value to memory with a particular endianness.
96 template <typename value_type, std::size_t alignment>
write(void * memory,value_type value,endianness endian)97 inline void write(void *memory, value_type value, endianness endian) {
98   value = byte_swap<value_type>(value, endian);
99   memcpy(LLVM_ASSUME_ALIGNED(
100              memory, (detail::PickAlignment<value_type, alignment>::value)),
101          &value, sizeof(value_type));
102 }
103 
104 template<typename value_type,
105          endianness endian,
106          std::size_t alignment>
write(void * memory,value_type value)107 inline void write(void *memory, value_type value) {
108   write<value_type, alignment>(memory, value, endian);
109 }
110 
111 template <typename value_type>
112 using make_unsigned_t = std::make_unsigned_t<value_type>;
113 
114 /// Read a value of a particular endianness from memory, for a location
115 /// that starts at the given bit offset within the first byte.
116 template <typename value_type, endianness endian, std::size_t alignment>
readAtBitAlignment(const void * memory,uint64_t startBit)117 inline value_type readAtBitAlignment(const void *memory, uint64_t startBit) {
118   assert(startBit < 8);
119   if (startBit == 0)
120     return read<value_type, endian, alignment>(memory);
121   else {
122     // Read two values and compose the result from them.
123     value_type val[2];
124     memcpy(&val[0],
125            LLVM_ASSUME_ALIGNED(
126                memory, (detail::PickAlignment<value_type, alignment>::value)),
127            sizeof(value_type) * 2);
128     val[0] = byte_swap<value_type, endian>(val[0]);
129     val[1] = byte_swap<value_type, endian>(val[1]);
130 
131     // Shift bits from the lower value into place.
132     make_unsigned_t<value_type> lowerVal = val[0] >> startBit;
133     // Mask off upper bits after right shift in case of signed type.
134     make_unsigned_t<value_type> numBitsFirstVal =
135         (sizeof(value_type) * 8) - startBit;
136     lowerVal &= ((make_unsigned_t<value_type>)1 << numBitsFirstVal) - 1;
137 
138     // Get the bits from the upper value.
139     make_unsigned_t<value_type> upperVal =
140         val[1] & (((make_unsigned_t<value_type>)1 << startBit) - 1);
141     // Shift them in to place.
142     upperVal <<= numBitsFirstVal;
143 
144     return lowerVal | upperVal;
145   }
146 }
147 
148 /// Write a value to memory with a particular endianness, for a location
149 /// that starts at the given bit offset within the first byte.
150 template <typename value_type, endianness endian, std::size_t alignment>
writeAtBitAlignment(void * memory,value_type value,uint64_t startBit)151 inline void writeAtBitAlignment(void *memory, value_type value,
152                                 uint64_t startBit) {
153   assert(startBit < 8);
154   if (startBit == 0)
155     write<value_type, endian, alignment>(memory, value);
156   else {
157     // Read two values and shift the result into them.
158     value_type val[2];
159     memcpy(&val[0],
160            LLVM_ASSUME_ALIGNED(
161                memory, (detail::PickAlignment<value_type, alignment>::value)),
162            sizeof(value_type) * 2);
163     val[0] = byte_swap<value_type, endian>(val[0]);
164     val[1] = byte_swap<value_type, endian>(val[1]);
165 
166     // Mask off any existing bits in the upper part of the lower value that
167     // we want to replace.
168     val[0] &= ((make_unsigned_t<value_type>)1 << startBit) - 1;
169     make_unsigned_t<value_type> numBitsFirstVal =
170         (sizeof(value_type) * 8) - startBit;
171     make_unsigned_t<value_type> lowerVal = value;
172     if (startBit > 0) {
173       // Mask off the upper bits in the new value that are not going to go into
174       // the lower value. This avoids a left shift of a negative value, which
175       // is undefined behavior.
176       lowerVal &= (((make_unsigned_t<value_type>)1 << numBitsFirstVal) - 1);
177       // Now shift the new bits into place
178       lowerVal <<= startBit;
179     }
180     val[0] |= lowerVal;
181 
182     // Mask off any existing bits in the lower part of the upper value that
183     // we want to replace.
184     val[1] &= ~(((make_unsigned_t<value_type>)1 << startBit) - 1);
185     // Next shift the bits that go into the upper value into position.
186     make_unsigned_t<value_type> upperVal = value >> numBitsFirstVal;
187     // Mask off upper bits after right shift in case of signed type.
188     upperVal &= ((make_unsigned_t<value_type>)1 << startBit) - 1;
189     val[1] |= upperVal;
190 
191     // Finally, rewrite values.
192     val[0] = byte_swap<value_type, endian>(val[0]);
193     val[1] = byte_swap<value_type, endian>(val[1]);
194     memcpy(LLVM_ASSUME_ALIGNED(
195                memory, (detail::PickAlignment<value_type, alignment>::value)),
196            &val[0], sizeof(value_type) * 2);
197   }
198 }
199 
200 } // end namespace endian
201 
202 namespace detail {
203 
204 template <typename ValueType, endianness Endian, std::size_t Alignment,
205           std::size_t ALIGN = PickAlignment<ValueType, Alignment>::value>
206 struct packed_endian_specific_integral {
207   using value_type = ValueType;
208   static constexpr endianness endian = Endian;
209   static constexpr std::size_t alignment = Alignment;
210 
211   packed_endian_specific_integral() = default;
212 
packed_endian_specific_integralpacked_endian_specific_integral213   explicit packed_endian_specific_integral(value_type val) { *this = val; }
214 
value_typepacked_endian_specific_integral215   operator value_type() const {
216     return endian::read<value_type, endian, alignment>(
217       (const void*)Value.buffer);
218   }
219 
220   void operator=(value_type newValue) {
221     endian::write<value_type, endian, alignment>(
222       (void*)Value.buffer, newValue);
223   }
224 
225   packed_endian_specific_integral &operator+=(value_type newValue) {
226     *this = *this + newValue;
227     return *this;
228   }
229 
230   packed_endian_specific_integral &operator-=(value_type newValue) {
231     *this = *this - newValue;
232     return *this;
233   }
234 
235   packed_endian_specific_integral &operator|=(value_type newValue) {
236     *this = *this | newValue;
237     return *this;
238   }
239 
240   packed_endian_specific_integral &operator&=(value_type newValue) {
241     *this = *this & newValue;
242     return *this;
243   }
244 
245 private:
246   struct {
247     alignas(ALIGN) char buffer[sizeof(value_type)];
248   } Value;
249 
250 public:
251   struct ref {
refpacked_endian_specific_integral::ref252     explicit ref(void *Ptr) : Ptr(Ptr) {}
253 
value_typepacked_endian_specific_integral::ref254     operator value_type() const {
255       return endian::read<value_type, endian, alignment>(Ptr);
256     }
257 
258     void operator=(value_type NewValue) {
259       endian::write<value_type, endian, alignment>(Ptr, NewValue);
260     }
261 
262   private:
263     void *Ptr;
264   };
265 };
266 
267 } // end namespace detail
268 
269 using ulittle16_t =
270     detail::packed_endian_specific_integral<uint16_t, little, unaligned>;
271 using ulittle32_t =
272     detail::packed_endian_specific_integral<uint32_t, little, unaligned>;
273 using ulittle64_t =
274     detail::packed_endian_specific_integral<uint64_t, little, unaligned>;
275 
276 using little16_t =
277     detail::packed_endian_specific_integral<int16_t, little, unaligned>;
278 using little32_t =
279     detail::packed_endian_specific_integral<int32_t, little, unaligned>;
280 using little64_t =
281     detail::packed_endian_specific_integral<int64_t, little, unaligned>;
282 
283 using aligned_ulittle16_t =
284     detail::packed_endian_specific_integral<uint16_t, little, aligned>;
285 using aligned_ulittle32_t =
286     detail::packed_endian_specific_integral<uint32_t, little, aligned>;
287 using aligned_ulittle64_t =
288     detail::packed_endian_specific_integral<uint64_t, little, aligned>;
289 
290 using aligned_little16_t =
291     detail::packed_endian_specific_integral<int16_t, little, aligned>;
292 using aligned_little32_t =
293     detail::packed_endian_specific_integral<int32_t, little, aligned>;
294 using aligned_little64_t =
295     detail::packed_endian_specific_integral<int64_t, little, aligned>;
296 
297 using ubig16_t =
298     detail::packed_endian_specific_integral<uint16_t, big, unaligned>;
299 using ubig32_t =
300     detail::packed_endian_specific_integral<uint32_t, big, unaligned>;
301 using ubig64_t =
302     detail::packed_endian_specific_integral<uint64_t, big, unaligned>;
303 
304 using big16_t =
305     detail::packed_endian_specific_integral<int16_t, big, unaligned>;
306 using big32_t =
307     detail::packed_endian_specific_integral<int32_t, big, unaligned>;
308 using big64_t =
309     detail::packed_endian_specific_integral<int64_t, big, unaligned>;
310 
311 using aligned_ubig16_t =
312     detail::packed_endian_specific_integral<uint16_t, big, aligned>;
313 using aligned_ubig32_t =
314     detail::packed_endian_specific_integral<uint32_t, big, aligned>;
315 using aligned_ubig64_t =
316     detail::packed_endian_specific_integral<uint64_t, big, aligned>;
317 
318 using aligned_big16_t =
319     detail::packed_endian_specific_integral<int16_t, big, aligned>;
320 using aligned_big32_t =
321     detail::packed_endian_specific_integral<int32_t, big, aligned>;
322 using aligned_big64_t =
323     detail::packed_endian_specific_integral<int64_t, big, aligned>;
324 
325 using unaligned_uint16_t =
326     detail::packed_endian_specific_integral<uint16_t, native, unaligned>;
327 using unaligned_uint32_t =
328     detail::packed_endian_specific_integral<uint32_t, native, unaligned>;
329 using unaligned_uint64_t =
330     detail::packed_endian_specific_integral<uint64_t, native, unaligned>;
331 
332 using unaligned_int16_t =
333     detail::packed_endian_specific_integral<int16_t, native, unaligned>;
334 using unaligned_int32_t =
335     detail::packed_endian_specific_integral<int32_t, native, unaligned>;
336 using unaligned_int64_t =
337     detail::packed_endian_specific_integral<int64_t, native, unaligned>;
338 
339 template <typename T>
340 using little_t = detail::packed_endian_specific_integral<T, little, unaligned>;
341 template <typename T>
342 using big_t = detail::packed_endian_specific_integral<T, big, unaligned>;
343 
344 template <typename T>
345 using aligned_little_t =
346     detail::packed_endian_specific_integral<T, little, aligned>;
347 template <typename T>
348 using aligned_big_t = detail::packed_endian_specific_integral<T, big, aligned>;
349 
350 namespace endian {
351 
read(const void * P,endianness E)352 template <typename T> inline T read(const void *P, endianness E) {
353   return read<T, unaligned>(P, E);
354 }
355 
read(const void * P)356 template <typename T, endianness E> inline T read(const void *P) {
357   return *(const detail::packed_endian_specific_integral<T, E, unaligned> *)P;
358 }
359 
read16(const void * P,endianness E)360 inline uint16_t read16(const void *P, endianness E) {
361   return read<uint16_t>(P, E);
362 }
read32(const void * P,endianness E)363 inline uint32_t read32(const void *P, endianness E) {
364   return read<uint32_t>(P, E);
365 }
read64(const void * P,endianness E)366 inline uint64_t read64(const void *P, endianness E) {
367   return read<uint64_t>(P, E);
368 }
369 
read16(const void * P)370 template <endianness E> inline uint16_t read16(const void *P) {
371   return read<uint16_t, E>(P);
372 }
read32(const void * P)373 template <endianness E> inline uint32_t read32(const void *P) {
374   return read<uint32_t, E>(P);
375 }
read64(const void * P)376 template <endianness E> inline uint64_t read64(const void *P) {
377   return read<uint64_t, E>(P);
378 }
379 
read16le(const void * P)380 inline uint16_t read16le(const void *P) { return read16<little>(P); }
read32le(const void * P)381 inline uint32_t read32le(const void *P) { return read32<little>(P); }
read64le(const void * P)382 inline uint64_t read64le(const void *P) { return read64<little>(P); }
read16be(const void * P)383 inline uint16_t read16be(const void *P) { return read16<big>(P); }
read32be(const void * P)384 inline uint32_t read32be(const void *P) { return read32<big>(P); }
read64be(const void * P)385 inline uint64_t read64be(const void *P) { return read64<big>(P); }
386 
write(void * P,T V,endianness E)387 template <typename T> inline void write(void *P, T V, endianness E) {
388   write<T, unaligned>(P, V, E);
389 }
390 
write(void * P,T V)391 template <typename T, endianness E> inline void write(void *P, T V) {
392   *(detail::packed_endian_specific_integral<T, E, unaligned> *)P = V;
393 }
394 
write16(void * P,uint16_t V,endianness E)395 inline void write16(void *P, uint16_t V, endianness E) {
396   write<uint16_t>(P, V, E);
397 }
write32(void * P,uint32_t V,endianness E)398 inline void write32(void *P, uint32_t V, endianness E) {
399   write<uint32_t>(P, V, E);
400 }
write64(void * P,uint64_t V,endianness E)401 inline void write64(void *P, uint64_t V, endianness E) {
402   write<uint64_t>(P, V, E);
403 }
404 
write16(void * P,uint16_t V)405 template <endianness E> inline void write16(void *P, uint16_t V) {
406   write<uint16_t, E>(P, V);
407 }
write32(void * P,uint32_t V)408 template <endianness E> inline void write32(void *P, uint32_t V) {
409   write<uint32_t, E>(P, V);
410 }
write64(void * P,uint64_t V)411 template <endianness E> inline void write64(void *P, uint64_t V) {
412   write<uint64_t, E>(P, V);
413 }
414 
write16le(void * P,uint16_t V)415 inline void write16le(void *P, uint16_t V) { write16<little>(P, V); }
write32le(void * P,uint32_t V)416 inline void write32le(void *P, uint32_t V) { write32<little>(P, V); }
write64le(void * P,uint64_t V)417 inline void write64le(void *P, uint64_t V) { write64<little>(P, V); }
write16be(void * P,uint16_t V)418 inline void write16be(void *P, uint16_t V) { write16<big>(P, V); }
write32be(void * P,uint32_t V)419 inline void write32be(void *P, uint32_t V) { write32<big>(P, V); }
write64be(void * P,uint64_t V)420 inline void write64be(void *P, uint64_t V) { write64<big>(P, V); }
421 
422 } // end namespace endian
423 
424 } // end namespace support
425 } // end namespace llvm
426 
427 #endif // LLVM_SUPPORT_ENDIAN_H
428