assumptions.h (4681B)
1 /*********************************************************************** 2 * Copyright (c) 2020 Pieter Wuille * 3 * Distributed under the MIT software license, see the accompanying * 4 * file COPYING or https://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 #if defined(SECP256K1_INT128_NATIVE) 14 #include "int128_native.h" 15 #endif 16 17 /* This library, like most software, relies on a number of compiler implementation defined (but not undefined) 18 behaviours. Although the behaviours we require are essentially universal we test them specifically here to 19 reduce the odds of experiencing an unwelcome surprise. 20 */ 21 22 #if defined(__has_attribute) 23 # if __has_attribute(__unavailable__) 24 __attribute__((__unavailable__("Don't call this function. It only exists because STATIC_ASSERT cannot be used outside a function."))) 25 # endif 26 #endif 27 static void haskellsecp256k1_v0_1_0_assumption_checker(void) { 28 /* Bytes are 8 bits. */ 29 STATIC_ASSERT(CHAR_BIT == 8); 30 31 /* No integer promotion for uint32_t. This ensures that we can multiply uintXX_t values where XX >= 32 32 without signed overflow, which would be undefined behaviour. */ 33 STATIC_ASSERT(UINT_MAX <= UINT32_MAX); 34 35 /* Conversions from unsigned to signed outside of the bounds of the signed type are 36 implementation-defined. Verify that they function as reinterpreting the lower 37 bits of the input in two's complement notation. Do this for conversions: 38 - from uint(N)_t to int(N)_t with negative result 39 - from uint(2N)_t to int(N)_t with negative result 40 - from int(2N)_t to int(N)_t with negative result 41 - from int(2N)_t to int(N)_t with positive result */ 42 43 /* To int8_t. */ 44 STATIC_ASSERT(((int8_t)(uint8_t)0xAB == (int8_t)-(int8_t)0x55)); 45 STATIC_ASSERT((int8_t)(uint16_t)0xABCD == (int8_t)-(int8_t)0x33); 46 STATIC_ASSERT((int8_t)(int16_t)(uint16_t)0xCDEF == (int8_t)(uint8_t)0xEF); 47 STATIC_ASSERT((int8_t)(int16_t)(uint16_t)0x9234 == (int8_t)(uint8_t)0x34); 48 49 /* To int16_t. */ 50 STATIC_ASSERT((int16_t)(uint16_t)0xBCDE == (int16_t)-(int16_t)0x4322); 51 STATIC_ASSERT((int16_t)(uint32_t)0xA1B2C3D4 == (int16_t)-(int16_t)0x3C2C); 52 STATIC_ASSERT((int16_t)(int32_t)(uint32_t)0xC1D2E3F4 == (int16_t)(uint16_t)0xE3F4); 53 STATIC_ASSERT((int16_t)(int32_t)(uint32_t)0x92345678 == (int16_t)(uint16_t)0x5678); 54 55 /* To int32_t. */ 56 STATIC_ASSERT((int32_t)(uint32_t)0xB2C3D4E5 == (int32_t)-(int32_t)0x4D3C2B1B); 57 STATIC_ASSERT((int32_t)(uint64_t)0xA123B456C789D012ULL == (int32_t)-(int32_t)0x38762FEE); 58 STATIC_ASSERT((int32_t)(int64_t)(uint64_t)0xC1D2E3F4A5B6C7D8ULL == (int32_t)(uint32_t)0xA5B6C7D8); 59 STATIC_ASSERT((int32_t)(int64_t)(uint64_t)0xABCDEF0123456789ULL == (int32_t)(uint32_t)0x23456789); 60 61 /* To int64_t. */ 62 STATIC_ASSERT((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL); 63 #if defined(SECP256K1_INT128_NATIVE) 64 STATIC_ASSERT((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL); 65 STATIC_ASSERT(((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL); 66 STATIC_ASSERT(((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL); 67 68 /* To int128_t. */ 69 STATIC_ASSERT((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL)); 70 #endif 71 72 /* Right shift on negative signed values is implementation defined. Verify that it 73 acts as a right shift in two's complement with sign extension (i.e duplicating 74 the top bit into newly added bits). */ 75 STATIC_ASSERT((((int8_t)0xE8) >> 2) == (int8_t)(uint8_t)0xFA); 76 STATIC_ASSERT((((int16_t)0xE9AC) >> 4) == (int16_t)(uint16_t)0xFE9A); 77 STATIC_ASSERT((((int32_t)0x937C918A) >> 9) == (int32_t)(uint32_t)0xFFC9BE48); 78 STATIC_ASSERT((((int64_t)0xA8B72231DF9CF4B9ULL) >> 19) == (int64_t)(uint64_t)0xFFFFF516E4463BF3ULL); 79 #if defined(SECP256K1_INT128_NATIVE) 80 STATIC_ASSERT((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL)); 81 #endif 82 83 /* This function is not supposed to be called. */ 84 VERIFY_CHECK(0); 85 } 86 87 #endif /* SECP256K1_ASSUMPTIONS_H */