а что тогда с 32-битным железом на 64-битной архитектуре?
Integral conversions
A prvalue of an integer type or of an unscoped enumeration type can be converted to any other integer type. If the conversion is listed under integral promotions, it is a promotion and not a conversion.
If the destination type is unsigned, the resulting value is the smallest unsigned value equal to the source value modulo 2n
where n is the number of bits used to represent the destination type.
That is, depending on whether the destination type is wider or narrower, signed integers are sign-extended[footnote 1] or truncated and unsigned integers are zero-extended or truncated respectively.
If the destination type is signed, the value does not change if the source integer can be represented in the destination type. Otherwise the result is implementation-defined (until C++20)the unique value of the destination type equal to the source value modulo 2n
where n is the number of bits used to represent the destination type. (since C++20). (Note that this is different from signed integer arithmetic overflow, which is undefined).
If the source type is bool, the value false is converted to zero and the value true is converted to the value one of the destination type (note that if the destination type is int, this is an integer promotion, not an integer conversion).
If the destination type is bool, this is a boolean conversion (see below).