Bitcoin Core  0.20.99
P2P Digital Currency
assumptions.h
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1 /**********************************************************************
2  * Copyright (c) 2020 Pieter Wuille *
3  * Distributed under the MIT software license, see the accompanying *
4  * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
5  **********************************************************************/
6 
7 #ifndef SECP256K1_ASSUMPTIONS_H
8 #define SECP256K1_ASSUMPTIONS_H
9 
10 #include <limits.h>
11 
12 #include "util.h"
13 
14 /* This library, like most software, relies on a number of compiler implementation defined (but not undefined)
15  behaviours. Although the behaviours we require are essentially universal we test them specifically here to
16  reduce the odds of experiencing an unwelcome surprise.
17 */
18 
20  /* This uses a trick to implement a static assertion in C89: a type with an array of negative size is not
21  allowed. */
22  int dummy_array[(
23  /* Bytes are 8 bits. */
24  (CHAR_BIT == 8) &&
25 
26  /* No integer promotion for uint32_t. This ensures that we can multiply uintXX_t values where XX >= 32
27  without signed overflow, which would be undefined behaviour. */
28  (UINT_MAX <= UINT32_MAX) &&
29 
30  /* Conversions from unsigned to signed outside of the bounds of the signed type are
31  implementation-defined. Verify that they function as reinterpreting the lower
32  bits of the input in two's complement notation. Do this for conversions:
33  - from uint(N)_t to int(N)_t with negative result
34  - from uint(2N)_t to int(N)_t with negative result
35  - from int(2N)_t to int(N)_t with negative result
36  - from int(2N)_t to int(N)_t with positive result */
37 
38  /* To int8_t. */
39  ((int8_t)(uint8_t)0xAB == (int8_t)-(int8_t)0x55) &&
40  ((int8_t)(uint16_t)0xABCD == (int8_t)-(int8_t)0x33) &&
41  ((int8_t)(int16_t)(uint16_t)0xCDEF == (int8_t)(uint8_t)0xEF) &&
42  ((int8_t)(int16_t)(uint16_t)0x9234 == (int8_t)(uint8_t)0x34) &&
43 
44  /* To int16_t. */
45  ((int16_t)(uint16_t)0xBCDE == (int16_t)-(int16_t)0x4322) &&
46  ((int16_t)(uint32_t)0xA1B2C3D4 == (int16_t)-(int16_t)0x3C2C) &&
47  ((int16_t)(int32_t)(uint32_t)0xC1D2E3F4 == (int16_t)(uint16_t)0xE3F4) &&
48  ((int16_t)(int32_t)(uint32_t)0x92345678 == (int16_t)(uint16_t)0x5678) &&
49 
50  /* To int32_t. */
51  ((int32_t)(uint32_t)0xB2C3D4E5 == (int32_t)-(int32_t)0x4D3C2B1B) &&
52  ((int32_t)(uint64_t)0xA123B456C789D012ULL == (int32_t)-(int32_t)0x38762FEE) &&
53  ((int32_t)(int64_t)(uint64_t)0xC1D2E3F4A5B6C7D8ULL == (int32_t)(uint32_t)0xA5B6C7D8) &&
54  ((int32_t)(int64_t)(uint64_t)0xABCDEF0123456789ULL == (int32_t)(uint32_t)0x23456789) &&
55 
56  /* To int64_t. */
57  ((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL) &&
58 #if defined(SECP256K1_WIDEMUL_INT128)
59  ((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL) &&
60  (((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL) &&
61  (((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL) &&
62 
63  /* To int128_t. */
64  ((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL)) &&
65 #endif
66 
67  /* Right shift on negative signed values is implementation defined. Verify that it
68  acts as a right shift in two's complement with sign extension (i.e duplicating
69  the top bit into newly added bits). */
70  ((((int8_t)0xE8) >> 2) == (int8_t)(uint8_t)0xFA) &&
71  ((((int16_t)0xE9AC) >> 4) == (int16_t)(uint16_t)0xFE9A) &&
72  ((((int32_t)0x937C918A) >> 9) == (int32_t)(uint32_t)0xFFC9BE48) &&
73  ((((int64_t)0xA8B72231DF9CF4B9ULL) >> 19) == (int64_t)(uint64_t)0xFFFFF516E4463BF3ULL) &&
74 #if defined(SECP256K1_WIDEMUL_INT128)
75  ((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL)) &&
76 #endif
77  1) * 2 - 1];
78 };
79 
80 #endif /* SECP256K1_ASSUMPTIONS_H */
int dummy_array[((CHAR_BIT==8) &&(UINT_MAX<=UINT32_MAX) &&((int8_t)(uint8_t) 0xAB==(int8_t) -(int8_t) 0x55) &&((int8_t)(uint16_t) 0xABCD==(int8_t) -(int8_t) 0x33) &&((int8_t)(int16_t)(uint16_t) 0xCDEF==(int8_t)(uint8_t) 0xEF) &&((int8_t)(int16_t)(uint16_t) 0x9234==(int8_t)(uint8_t) 0x34) &&((int16_t)(uint16_t) 0xBCDE==(int16_t) -(int16_t) 0x4322) &&((int16_t)(uint32_t) 0xA1B2C3D4==(int16_t) -(int16_t) 0x3C2C) &&((int16_t)(int32_t)(uint32_t) 0xC1D2E3F4==(int16_t)(uint16_t) 0xE3F4) &&((int16_t)(int32_t)(uint32_t) 0x92345678==(int16_t)(uint16_t) 0x5678) &&((int32_t)(uint32_t) 0xB2C3D4E5==(int32_t) -(int32_t) 0x4D3C2B1B) &&((int32_t)(uint64_t) 0xA123B456C789D012ULL==(int32_t) -(int32_t) 0x38762FEE) &&((int32_t)(int64_t)(uint64_t) 0xC1D2E3F4A5B6C7D8ULL==(int32_t)(uint32_t) 0xA5B6C7D8) &&((int32_t)(int64_t)(uint64_t) 0xABCDEF0123456789ULL==(int32_t)(uint32_t) 0x23456789) &&((int64_t)(uint64_t) 0xB123C456D789E012ULL==(int64_t) -(int64_t) 0x4EDC3BA928761FEEULL) &&((((int8_t) 0xE8) >> 2)==(int8_t)(uint8_t) 0xFA) &&((((int16_t) 0xE9AC) >> 4)==(int16_t)(uint16_t) 0xFE9A) &&((((int32_t) 0x937C918A) >> 9)==(int32_t)(uint32_t) 0xFFC9BE48) &&((((int64_t) 0xA8B72231DF9CF4B9ULL) >> 19)==(int64_t)(uint64_t) 0xFFFFF516E4463BF3ULL) &&1) *2 - 1]
Definition: assumptions.h:77