mirror of https://github.com/bitcoin/bitcoin
84 lines
4.3 KiB
C
84 lines
4.3 KiB
C
/***********************************************************************
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* Copyright (c) 2020 Pieter Wuille *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
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***********************************************************************/
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#ifndef SECP256K1_ASSUMPTIONS_H
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#define SECP256K1_ASSUMPTIONS_H
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#include <limits.h>
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#include "util.h"
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#if defined(SECP256K1_INT128_NATIVE)
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#include "int128_native.h"
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#endif
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/* This library, like most software, relies on a number of compiler implementation defined (but not undefined)
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behaviours. Although the behaviours we require are essentially universal we test them specifically here to
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reduce the odds of experiencing an unwelcome surprise.
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*/
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struct secp256k1_assumption_checker {
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/* This uses a trick to implement a static assertion in C89: a type with an array of negative size is not
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allowed. */
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int dummy_array[(
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/* Bytes are 8 bits. */
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(CHAR_BIT == 8) &&
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/* No integer promotion for uint32_t. This ensures that we can multiply uintXX_t values where XX >= 32
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without signed overflow, which would be undefined behaviour. */
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(UINT_MAX <= UINT32_MAX) &&
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/* Conversions from unsigned to signed outside of the bounds of the signed type are
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implementation-defined. Verify that they function as reinterpreting the lower
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bits of the input in two's complement notation. Do this for conversions:
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- from uint(N)_t to int(N)_t with negative result
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- from uint(2N)_t to int(N)_t with negative result
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- from int(2N)_t to int(N)_t with negative result
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- from int(2N)_t to int(N)_t with positive result */
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/* To int8_t. */
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((int8_t)(uint8_t)0xAB == (int8_t)-(int8_t)0x55) &&
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((int8_t)(uint16_t)0xABCD == (int8_t)-(int8_t)0x33) &&
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((int8_t)(int16_t)(uint16_t)0xCDEF == (int8_t)(uint8_t)0xEF) &&
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((int8_t)(int16_t)(uint16_t)0x9234 == (int8_t)(uint8_t)0x34) &&
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/* To int16_t. */
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((int16_t)(uint16_t)0xBCDE == (int16_t)-(int16_t)0x4322) &&
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((int16_t)(uint32_t)0xA1B2C3D4 == (int16_t)-(int16_t)0x3C2C) &&
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((int16_t)(int32_t)(uint32_t)0xC1D2E3F4 == (int16_t)(uint16_t)0xE3F4) &&
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((int16_t)(int32_t)(uint32_t)0x92345678 == (int16_t)(uint16_t)0x5678) &&
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/* To int32_t. */
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((int32_t)(uint32_t)0xB2C3D4E5 == (int32_t)-(int32_t)0x4D3C2B1B) &&
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((int32_t)(uint64_t)0xA123B456C789D012ULL == (int32_t)-(int32_t)0x38762FEE) &&
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((int32_t)(int64_t)(uint64_t)0xC1D2E3F4A5B6C7D8ULL == (int32_t)(uint32_t)0xA5B6C7D8) &&
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((int32_t)(int64_t)(uint64_t)0xABCDEF0123456789ULL == (int32_t)(uint32_t)0x23456789) &&
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/* To int64_t. */
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((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL) &&
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#if defined(SECP256K1_INT128_NATIVE)
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((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL) &&
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(((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL) &&
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(((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL) &&
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/* To int128_t. */
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((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL)) &&
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#endif
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/* Right shift on negative signed values is implementation defined. Verify that it
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acts as a right shift in two's complement with sign extension (i.e duplicating
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the top bit into newly added bits). */
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((((int8_t)0xE8) >> 2) == (int8_t)(uint8_t)0xFA) &&
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((((int16_t)0xE9AC) >> 4) == (int16_t)(uint16_t)0xFE9A) &&
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((((int32_t)0x937C918A) >> 9) == (int32_t)(uint32_t)0xFFC9BE48) &&
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((((int64_t)0xA8B72231DF9CF4B9ULL) >> 19) == (int64_t)(uint64_t)0xFFFFF516E4463BF3ULL) &&
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#if defined(SECP256K1_INT128_NATIVE)
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((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL)) &&
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#endif
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1) * 2 - 1];
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};
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#endif /* SECP256K1_ASSUMPTIONS_H */
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