assumptions: Use new STATIC_ASSERT macro

This also splits the big "&&" expression into separate expressions. If we ever see an assertion fail, the error message will tell it precisely which one failed.
real-or-random · Jan 8, 2024 · ba5d72d · ba5d72d
1 parent e53c2d9
commit ba5d72d
Showing 1 changed file with 52 additions and 48 deletions.
diff --git a/src/assumptions.h b/src/assumptions.h
@@ -19,65 +19,69 @@
    reduce the odds of experiencing an unwelcome surprise.
 */
 
-struct secp256k1_assumption_checker {
-    /* This uses a trick to implement a static assertion in C89: a type with an array of negative size is not
-       allowed. */
-    int dummy_array[(
-        /* Bytes are 8 bits. */
-        (CHAR_BIT == 8) &&
+#if defined(__has_attribute)
+# if __has_attribute(__unavailable__)
+__attribute__((__unavailable__("Don't call this function. It only exists because STATIC_ASSERT cannot be used outside a function.")))
+# endif
+#endif
+static void secp256k1_assumption_checker(void) {
+    /* Bytes are 8 bits. */
+    STATIC_ASSERT(CHAR_BIT == 8);
 
-        /* No integer promotion for uint32_t. This ensures that we can multiply uintXX_t values where XX >= 32
-           without signed overflow, which would be undefined behaviour. */
-        (UINT_MAX <= UINT32_MAX) &&
+    /* No integer promotion for uint32_t. This ensures that we can multiply uintXX_t values where XX >= 32
+       without signed overflow, which would be undefined behaviour. */
+    STATIC_ASSERT(UINT_MAX <= UINT32_MAX);
 
-        /* Conversions from unsigned to signed outside of the bounds of the signed type are
-           implementation-defined. Verify that they function as reinterpreting the lower
-           bits of the input in two's complement notation. Do this for conversions:
-           - from uint(N)_t to int(N)_t with negative result
-           - from uint(2N)_t to int(N)_t with negative result
-           - from int(2N)_t to int(N)_t with negative result
-           - from int(2N)_t to int(N)_t with positive result */
+    /* Conversions from unsigned to signed outside of the bounds of the signed type are
+       implementation-defined. Verify that they function as reinterpreting the lower
+       bits of the input in two's complement notation. Do this for conversions:
+       - from uint(N)_t to int(N)_t with negative result
+       - from uint(2N)_t to int(N)_t with negative result
+       - from int(2N)_t to int(N)_t with negative result
+       - from int(2N)_t to int(N)_t with positive result */
 
-        /* To int8_t. */
-        ((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) &&
+    /* To int8_t. */
+    STATIC_ASSERT(((int8_t)(uint8_t)0xAB == (int8_t)-(int8_t)0x55));
+    STATIC_ASSERT((int8_t)(uint16_t)0xABCD == (int8_t)-(int8_t)0x33);
+    STATIC_ASSERT((int8_t)(int16_t)(uint16_t)0xCDEF == (int8_t)(uint8_t)0xEF);
+    STATIC_ASSERT((int8_t)(int16_t)(uint16_t)0x9234 == (int8_t)(uint8_t)0x34);
 
-        /* To int16_t. */
-        ((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) &&
+    /* To int16_t. */
+    STATIC_ASSERT((int16_t)(uint16_t)0xBCDE == (int16_t)-(int16_t)0x4322);
+    STATIC_ASSERT((int16_t)(uint32_t)0xA1B2C3D4 == (int16_t)-(int16_t)0x3C2C);
+    STATIC_ASSERT((int16_t)(int32_t)(uint32_t)0xC1D2E3F4 == (int16_t)(uint16_t)0xE3F4);
+    STATIC_ASSERT((int16_t)(int32_t)(uint32_t)0x92345678 == (int16_t)(uint16_t)0x5678);
 
-        /* To int32_t. */
-        ((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) &&
+    /* To int32_t. */
+    STATIC_ASSERT((int32_t)(uint32_t)0xB2C3D4E5 == (int32_t)-(int32_t)0x4D3C2B1B);
+    STATIC_ASSERT((int32_t)(uint64_t)0xA123B456C789D012ULL == (int32_t)-(int32_t)0x38762FEE);
+    STATIC_ASSERT((int32_t)(int64_t)(uint64_t)0xC1D2E3F4A5B6C7D8ULL == (int32_t)(uint32_t)0xA5B6C7D8);
+    STATIC_ASSERT((int32_t)(int64_t)(uint64_t)0xABCDEF0123456789ULL == (int32_t)(uint32_t)0x23456789);
 
-        /* To int64_t. */
-        ((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL) &&
+    /* To int64_t. */
+    STATIC_ASSERT((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL);
 #if defined(SECP256K1_INT128_NATIVE)
-        ((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL) &&
-        (((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL) &&
-        (((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL) &&
+    STATIC_ASSERT((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL);
+    STATIC_ASSERT(((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL);
+    STATIC_ASSERT(((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL);
 
-        /* To int128_t. */
-        ((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL)) &&
+    /* To int128_t. */
+    STATIC_ASSERT((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL));
 #endif
 
-        /* Right shift on negative signed values is implementation defined. Verify that it
-           acts as a right shift in two's complement with sign extension (i.e duplicating
-           the top bit into newly added bits). */
-        ((((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) &&
+    /* Right shift on negative signed values is implementation defined. Verify that it
+       acts as a right shift in two's complement with sign extension (i.e duplicating
+       the top bit into newly added bits). */
+    STATIC_ASSERT((((int8_t)0xE8) >> 2) == (int8_t)(uint8_t)0xFA);
+    STATIC_ASSERT((((int16_t)0xE9AC) >> 4) == (int16_t)(uint16_t)0xFE9A);
+    STATIC_ASSERT((((int32_t)0x937C918A) >> 9) == (int32_t)(uint32_t)0xFFC9BE48);
+    STATIC_ASSERT((((int64_t)0xA8B72231DF9CF4B9ULL) >> 19) == (int64_t)(uint64_t)0xFFFFF516E4463BF3ULL);
 #if defined(SECP256K1_INT128_NATIVE)
-        ((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL)) &&
+    STATIC_ASSERT((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL));
 #endif
-    1) * 2 - 1];
-};
+
+    /* This function is not supposed to be called. */
+    VERIFY_CHECK(0);
+}
 
 #endif /* SECP256K1_ASSUMPTIONS_H */