The implementation principle of rend_util.sample_pdf() and sample_cdf()?

[YinGuoX]

Thank you for your work and summary. I have learned a lot, but due to the limitations of knowledge, I still have some doubts. I sincerely hope you can help me solve my doubts.

Q1：Although the functions of sample_pdf() and sample_cdf() can be known according to the functions of the code, I still can't understand the specific internal details of sample_pdf() and sample_cdf(). If you are free, I hope you can answer or recommend relevant knowledge materials.

Thank you very much！
Look forward to your reply.