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>"The instruction set is complex, convenient, high level, and slow." Could you elaborate on how The DEC VAX ISA was complex yet also convenient? I feel like th
by bogomipz 4y ago
>"The instruction set is complex, convenient, high level, and slow."
Could you elaborate on how The DEC VAX ISA was complex yet also convenient? I feel like those two characteristic are at odds with each other. Or does complexity and convenience refer to different aspects i.e implementation vs use?
- msla 4y agoConvenient to assembly code authors and compiler writers. It had a lot of addressing modes and they were all almost completely orthogonal, which meant you could use them on any register, source or destination, and the hardware and microcode had to figure out how to not only execute the instruction, but back out all of the state if a fault occurred and the CPU had to handle it. In addition to its addressing modes, the VAX also had complicated opcodes, such as POLY, which evaluated a polynomial of arbitrary degree by taking an X value and a pointer to an array of coefficients.