This is as used in "Optimized Implementation of SM4 on AVR Microcontrollers and ARM Processors" by Hyeokdong Kwon, Hyunjun Kim, Eum Si Woo, Minjoo Shim, Wai-Kong Lee, Zhi Hu, Hwajeong Seo, eprint.iacr.org/2021/667.
The actual code is taken from Appendix B of the IETF data tracker.
The main program uses an undeclared variable, debug, which appears to be intended to force enable/disable debug_print. In order for this program to compile, we have replaced this with #define DEBUG 1 and #define DEBUG 0 as appopriate.
Numerous warnings about correct printf flags, due to the SM4_ROUNDS macro.