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And the txr lisp virtual machine there is a t0 register, which is always nil, and that symbol can be used as an alias for it in the assembly. This was conscious
by kazinator 2y ago
And the txr lisp virtual machine there is a t0 register, which is always nil, and that symbol can be used as an alias for it in the assembly. This was consciously inspired by the MIPS $zero.
A write to t0 is not simply ignored. It will generate an exception. Another MIPS-like thing is that t1 is an assembler temporary.
- amszmidt 2y agoThe CADR had a convention for the A and M memory (essentially what we would call registers today) for the Lisp Machine microcode where the first 32 locations had special meaning. Location 2 was for constant 0, and 3 for constant -1.