编写一个返回16位表达式的函数

Question

The question following is excerpted from exercise 6, chapter 7, A book on C.

6. Write a function that will extract every other bit position from a 32-bit expression. The result should be returned as a 16-bit expression. Your function should work on machines having either 2- or 4-byte words.

Now there are two key points I do not understand about this question:

• What does it mean, "extract every other bit position"? I really do not understand this. For example, a 32-bit expression: 00000001 00000000 00000000 10011110, what can "extract every other bit position" do?
• The question seems to contradict itself: "Extract every other bit position from a 32-bit expression," then "your function should work on machines having either 2- or 4-byte words," but 2-byte words are only 16-bit expression; how can I extract every other bit position from an expression that is "both" 32-bit and 16-bit?

This question really makes no senses. One of the things I really hate about this book is, compared to C prorgamming written by Kochan, which I have no problems at all in understanding its questions, so dense to understand with respect to exercise questions. Or may be I am just stupid!

Answer 1

"every other bit" means each either bits 0, 2, 4, 6 ... or bits 1, 3, 5, 7 ...

If you start with 32 bits and take each other bit then your result is 16 bits.