Defect Report #269

Submitter: UK C Panel
Submission Date: 2001-09-07
Source: Clive D.W. Feather <clive@demon.net>
Version: 1.2
Date: 2002-05-15
Subject: lacunae in exact-width integer types

[#1] The typedef name intN_t designates a signed integer type with width N, no padding bits, and a two's complement representation. Thus, int8_t denotes a signed integer type with a width of exactly 8 bits.

[#2] The typedef name uintN_t designates an unsigned integer type with width N. Thus, uint24_t denotes an unsigned integer type with a width of exactly 24 bits.

[#3] These types are optional. However, if an implementation provides integer types with widths of 8, 16, 32, or 64 bits, it shall define the corresponding typedef names.

The requirements for no padding bits and two's complement were added at a late stage, and the implications to the text weren't fully thought through. In particular:

• the second sentence of #1 is inconsistent with the first;
• the unsigned types should also have the "no padding bits" requirement (it can be derived from the requirement to provide both or neither of these types and the requirement that they have the same size, but it ought to be spelled out);
• the requirements in #3 aren't the same as those in #1, so an implementation can't have 8 bit types with padding bits or a sign-and-magnitude representation.

Suggested Technical Corrigendum

Change this section to read:

[#1] The typedef name intN_t designates a signed integer type with width N, no padding bits, and a two's complement representation. Thus, int8_t denotes a signed integer type with a width of exactly 8 bits and those other properties.

[#2] The typedef name uintN_t designates an unsigned integer type with width N and no padding bits. Thus, uint24_t denotes an unsigned integer type with a width of exactly 24 bits and no padding bits.

[#3] These types are optional. However, if an implementation provides integer types with widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a two's complement representation, it shall define the corresponding typedef names.

Or, alternatively:

[#3] These types are optional. However, if an implementation has a type with width 8, 16, 32, or 64 bits that meet the above requirements, it shall define the corresponding typedef names.

Committee Response

The first bullet point is false; while the second sentence is not a complete specification, it does not contradict the first sentence.

Technical Corrigendum

Change 7.18.1.1#3 to read:

These types are optional. However, if an implementation provides integer types with widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a two's complement representation, it shall define the corresponding typedef names.

Committee Discussion

The Committee believes that suggestion 2 (about unsigned types) should be considered for a future revision of the Standard.

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