Hacker News Reader

anon_comenter9on United States loses AAA credit rating from S&P

Actually health care costs are growing far larger and faster than the cost of social security.

anon_comenter9on TinyVM: A lightweight, fast virtual machine in < 500 lines of ANSI C

Thinking about it, that sounds like inline threading

http://blog.mozilla.com/dmandelin/2008/08/27/inline-threadin...

anon_comenter9on TinyVM: A lightweight, fast virtual machine in < 500 lines of ANSI C

You are probably talking about threaded code which is described in "The Structure and Performance of Efficient Interpreters" http://www.jilp.org/vol5/v5paper12.pdf

With real code examples

anon_comenter9on TinyVM: A lightweight, fast virtual machine in < 500 lines of ANSI C

Exactamundo!

anon_comenter9on TinyVM: A lightweight, fast virtual machine in < 500 lines of ANSI C

Unless this is relying on the compiler optimizing this, the dispatch looks to be not good

if(vm->pProgram->instr[instr_idx] == MOV) arg0 = arg1; else if(vm->pProgram->instr[instr_idx] == PUSH) stack_push(vm->pStack, arg0); else if(vm->pProgram->instr[instr_idx] == POP) stack_pop(vm->pStack, arg0); else if(vm->pProgram->instr[instr_idx] == INC) ++(arg0); else if(vm->pProgram->instr[instr_idx] == DEC) --(arg0); else if(vm->pProgram->instr[instr_idx] == ADD) arg0 += arg1; else if(vm->pProgram->instr[instr_idx] == SUB) arg0 -= arg1; else if(vm->pProgram->instr[instr_idx] == MUL) arg0 = arg1; else if(vm->pProgram->instr[instr_idx] == DIV) arg0 /= arg1; else if(vm->pProgram->instr[instr_idx] == MOD) vm->pMemory->remainder = arg0 % arg1; else if(vm->pProgram->instr[instr_idx] == REM) arg0 = vm->pMemory->remainder; else if(vm->pProgram->instr[instr_idx] == NOT) arg0 = ~(arg0); else if(vm->pProgram->instr[instr_idx] == XOR) arg0 ^= arg1; else if(vm->pProgram->instr[instr_idx] == OR) arg0 |= arg1; else if(vm->pProgram->instr[instr_idx] == AND) arg0 &= arg1; else if(vm->pProgram->instr[instr_idx] == SHL) arg0 <<= arg1; else if(vm->pProgram->instr[instr_idx] == SHR) arg0 >>= arg1; else if(vm->pProgram->instr[instr_idx] == CMP) vm->pMemory->FLAGS = ((arg0 == arg1) | (arg0 > arg1) << 1); else if(vm->pProgram->instr[instr_idx] == JMP) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JE && (vm->pMemory->FLAGS & 0x1)) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JNE && !(vm->pMemory->FLAGS & 0x1)) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JG && (vm->pMemory->FLAGS & 0x2)) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JGE && (vm->pMemory->FLAGS & 0x3)) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JL && !(vm->pMemory->FLAGS & 0x3)) instr_idx = arg0 - 1; else if(vm->pProgram->instr[instr_idx] == JLE && !(vm->pMemory->FLAGS & 0x2)) instr_idx = *arg0 - 1;