From: anton@mips.complang.tuwien.ac.at   
      
   BGB  writes:   
   >Can note that GCC seemingly doesn't support 128-bit integers on 64-bit   
   >RISC-V.   
      
   What makes you think so?  It has certainly worked every time I tried   
   it.  E.g., Gforth's "configure" reports:   
      
   checking size of __int128_t... 16   
   checking size of __uint128_t... 16   
   [...]   
   checking for a C type for double-cells... __int128_t   
   checking for a C type for unsigned double-cells... __uint128_t   
      
   That's with gcc 10.3.1   
      
   >Also, doing 128-bit arithmetic on RV64 kinda sucks as there is   
   >basically no good way to do extended precision arithmetic (essentially,   
   >the ISA offers nothing more here than what C already gives you).   
   >   
   >Like, you can do what is essentially:   
   >   c_lo = a_lo + b_lo;   
   >   c_hi = a_hi + b_hi;   
   >   if((c_lo     c_hi++;   
      
   You only need to check for c_lo   
      
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