x86-64 could repurpose the Adjust flag (bit 4 of EFLAGS) for this. It is not longer used, since BCD instructions were deprecated in the x86->x86-64 transition.

x86-64 could repurpose the Adjust flag (bit 4 of EFLAGS) for this. It is not longer used, since BCD instructions were deprecated in the x86->x86-64 transition. There is also precedent in the last few years for new instructions that change flag semantics: ADCX and ADOX.