这是 C 标准中整数类型符号位定义的错误吗？
Is this a mistake in the definition of the sign bit for integer types in the C standard?
我认为 ISO/IEC 9899:TC3 C standard
的第 6.2.6.2 节中描述整数类型的符号位有错误
For signed integer types, the bits of the object representation shall
be divided into three groups: value bits, padding bits, and the sign
bit. There need not be any padding bits; there shall be exactly one
sign bit. Each bit that is a value bit shall have the same value as
the same bit in the object representation of the corresponding
unsigned type (if there are M value bits in the signed type and N in
the unsigned type, then M ≤ N). If the sign bit is zero, it shall not
affect the resulting value. If the sign bit is one, the value shall be
modified in one of the following ways:
- the corresponding value with sign bit 0 is negated (sign and magnitude);
- the sign bit has the value −(2^N) (two’s complement);
- the sign bit has the value −(2^N − 1) (ones’ complement)
上一节定义N为有符号类型的值位数，这里为无符号类型的值位数
以每个字节 8 位和二进制补码的 signed char 为例，这表示符号位的值为 -(2^8) =-256 而不是 -(2^7) = -128.
我认为标准应该在开头的段落中切换 M 和 N 或更改符号位的定义以使用 M:
- the sign bit has the value −(2^M) (two’s complement);
- the sign bit has the value −(2^M − 1) (ones’ complement)
我是不是漏掉了什么，或者这是一个错误？
在 C11 draft standard（Jonathan Leffler 确认最终标准也包含此措辞）中确实从使用 N 切换到使用 M:
- the sign bit has the value −(2M) (two’s complement);
- the sign bit has the value −(2M − 1) (ones’ complement).
我找不到缺陷报告，但这取决于：
If there are N value bits
第 1 段也适用于第 2 段，这并不是一个不合理的解释，它只是高度含糊不清：
(if there are
M value bits in the signed type and N in the unsigned type, then M <= N)
我认为 ISO/IEC 9899:TC3 C standard
的第 6.2.6.2 节中描述整数类型的符号位有错误For signed integer types, the bits of the object representation shall be divided into three groups: value bits, padding bits, and the sign bit. There need not be any padding bits; there shall be exactly one sign bit. Each bit that is a value bit shall have the same value as the same bit in the object representation of the corresponding unsigned type (if there are M value bits in the signed type and N in the unsigned type, then M ≤ N). If the sign bit is zero, it shall not affect the resulting value. If the sign bit is one, the value shall be modified in one of the following ways:
- the corresponding value with sign bit 0 is negated (sign and magnitude);
- the sign bit has the value −(2^N) (two’s complement);
- the sign bit has the value −(2^N − 1) (ones’ complement)
上一节定义N为有符号类型的值位数，这里为无符号类型的值位数
以每个字节 8 位和二进制补码的 signed char 为例，这表示符号位的值为 -(2^8) =-256 而不是 -(2^7) = -128.
我认为标准应该在开头的段落中切换 M 和 N 或更改符号位的定义以使用 M:
- the sign bit has the value −(2^M) (two’s complement);
- the sign bit has the value −(2^M − 1) (ones’ complement)
我是不是漏掉了什么，或者这是一个错误？
在 C11 draft standard（Jonathan Leffler 确认最终标准也包含此措辞）中确实从使用 N 切换到使用 M:
- the sign bit has the value −(2M) (two’s complement);
- the sign bit has the value −(2M − 1) (ones’ complement).
我找不到缺陷报告，但这取决于：
If there are N value bits
第 1 段也适用于第 2 段，这并不是一个不合理的解释，它只是高度含糊不清：
(if there are M value bits in the signed type and N in the unsigned type, then M <= N)