diff options
Diffstat (limited to 'subx/010---vm.cc')
| -rw-r--r-- | subx/010---vm.cc | 37 |
1 files changed, 7 insertions, 30 deletions
diff --git a/subx/010---vm.cc b/subx/010---vm.cc index 31e5608f..18f69035 100644 --- a/subx/010---vm.cc +++ b/subx/010---vm.cc @@ -62,7 +62,10 @@ put_new(Help, "registers", "- the sign flag (SF): usually set if an arithmetic result is negative, or\n" " reset if not.\n" "- the zero flag (ZF): usually set if a result is zero, or reset if not.\n" - "- the overflow flag (OF): usually set if an arithmetic result overflows.\n" + "- the carry flag (CF): usually set if an arithmetic result overflows by just one bit.\n" + " Useful for operating on unsigned numbers.\n" + "- the overflow flag (OF): usually set if an arithmetic result overflows by more than one bit.\n" + " Useful for operating on signed numbers.\n" "The flag bits are read by conditional jumps.\n" "\n" "For complete details on how different instructions update the flags, consult the IA-32\n" @@ -78,36 +81,10 @@ put_new(Help, "registers", // the subset of x86 flag registers we care about bool SF = false; // sign flag bool ZF = false; // zero flag +bool CF = false; // carry flag bool OF = false; // overflow flag :(before "End Reset") -SF = ZF = OF = false; - -//: how the flag registers are updated after each instruction - -:(before "End Includes") -// Combine 'arg1' and 'arg2' with arithmetic operation 'op' and store the -// result in 'arg1', then update flags. -// beware: no side-effects in args -#define BINARY_ARITHMETIC_OP(op, arg1, arg2) { \ - /* arg1 and arg2 must be signed */ \ - int64_t tmp = arg1 op arg2; \ - arg1 = arg1 op arg2; \ - trace(Callstack_depth+1, "run") << "storing 0x" << HEXWORD << arg1 << end(); \ - SF = (arg1 < 0); \ - ZF = (arg1 == 0); \ - OF = (arg1 != tmp); \ -} - -// Combine 'arg1' and 'arg2' with bitwise operation 'op' and store the result -// in 'arg1', then update flags. -#define BINARY_BITWISE_OP(op, arg1, arg2) { \ - /* arg1 and arg2 must be unsigned */ \ - arg1 = arg1 op arg2; \ - trace(Callstack_depth+1, "run") << "storing 0x" << HEXWORD << arg1 << end(); \ - SF = (arg1 >> 31); \ - ZF = (arg1 == 0); \ - OF = false; \ -} +SF = ZF = CF = OF = false; //:: simulated RAM @@ -374,7 +351,7 @@ void dump_registers() { if (i > 0) out << "; "; out << " " << i << ": " << std::hex << std::setw(8) << std::setfill('_') << Reg[i].u; } - out << " -- SF: " << SF << "; ZF: " << ZF << "; OF: " << OF; + out << " -- SF: " << SF << "; ZF: " << ZF << "; CF: " << CF << "; OF: " << OF; trace(Callstack_depth+1, "run") << out.str() << end(); } |