An issue in the book "ARM Embedded System Development-software design and optimization"

<ARM Embedded System Development-Software Design and Optimization> in Chapter 5 of this book, section 5.10.2 converts division into multiplication (Chinese p133 page). In this section, there is a sentence: in mathematics, the 32-bit right shift will bring an error E2. The first question: what is the error here and how does it come from?
In the following example, the title 5.13 shows how Division is actually converted to multiplication. according to its program, I didn't see how it converts division to multiplication. In its program, there is a sentence: Unsigned int S = 0 xffffffffu/d; isn't this sentence a division operation? What is the difference between this and q = N/d, and r = N-Q * D?
The following section is for reference. Thank you!