c - C中较大的整数到较小的无符号类型转换

Question

我正在通过 k & r。我在理解第 197 页(A6 节)中的以下几行时遇到问题

Integral conversions: any integer is converted to a given unsigned type by finding the smallest non negative value that is congruent to that integer,modulo one more than the largest value that can be represented in the unsigned type.

任何人都可以详细解释一下吗？谢谢

Answer 1

这意味着只计算低位，高位将被丢弃。

例如:

01111111 11111111 11110000 00001111

当转换为 16 位 unsigned short 时将是:

11110000 00001111

这在数学上有效地表达为:

target_value = value % (target_type_max+1)           ( % = modulus operator )