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5113 - x86's integer division (idiv) instruction

This commit is contained in:
Kartik Agaram 2019-04-21 23:35:23 -07:00
parent 0824f5df85
commit a78deb23b5
2 changed files with 94 additions and 2 deletions
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94
subx/013direct_addressing.cc
View File

@ -119,7 +119,7 @@ case 0x29: { // subtract r32 from r/m32
//:: multiply
:(before "End Initialize Op Names")
put_new(Name, "f7", "negate/multiply rm32 (with EAX if necessary) depending on subop (neg/mul)");
put_new(Name, "f7", "negate/multiply/divide rm32 (with EAX and EDX if necessary) depending on subop (neg/mul/idiv)");
:(code)
void test_multiply_eax_by_r32() {
@ -251,6 +251,98 @@ void test_negate_can_overflow() {
);
}
//:: divide with remainder
void test_divide_eax_by_rm32() {
Reg[EAX].u = 7;
Reg[EDX].u = 0;
Reg[ECX].i = 3;
run(
"== 0x1\n" // code segment
// op ModR/M SIB displacement immediate
" f7 f9 \n" // multiply EAX by ECX
// ModR/M in binary: 11 (direct mode) 111 (subop idiv) 001 (divisor ECX)
);
CHECK_TRACE_CONTENTS(
"run: operate on r/m32\n"
"run: r/m32 is ECX\n"
"run: subop: divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX\n"
"run: quotient: 0x00000002\n"
"run: remainder: 0x00000001\n"
);
}
:(before "End Op f7 Subops")
case 7: { // divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX
trace(Callstack_depth+1, "run") << "subop: divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX" << end();
int64_t dividend = static_cast<int64_t>((static_cast<uint64_t>(Reg[EDX].u) << 32) | Reg[EAX].u);
int32_t divisor = *arg1;
assert(divisor != 0);
Reg[EAX].i = dividend/divisor; // quotient
Reg[EDX].i = dividend%divisor; // remainder
trace(Callstack_depth+1, "run") << "quotient: 0x" << HEXWORD << Reg[EAX].i << end();
trace(Callstack_depth+1, "run") << "remainder: 0x" << HEXWORD << Reg[EDX].i << end();
break;
}
:(code)
void test_divide_eax_by_negative_rm32() {
Reg[EAX].u = 7;
Reg[EDX].u = 0;
Reg[ECX].i = -3;
run(
"== 0x1\n" // code segment
// op ModR/M SIB displacement immediate
" f7 f9 \n" // multiply EAX by ECX
// ModR/M in binary: 11 (direct mode) 111 (subop idiv) 001 (divisor ECX)
);
CHECK_TRACE_CONTENTS(
"run: operate on r/m32\n"
"run: r/m32 is ECX\n"
"run: subop: divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX\n"
"run: quotient: 0xfffffffe\n" // -2
"run: remainder: 0x00000001\n"
);
}
void test_divide_negative_eax_by_rm32() {
Reg[EAX].i = -7;
Reg[EDX].i = -1; // sign extend
Reg[ECX].i = 3;
run(
"== 0x1\n" // code segment
// op ModR/M SIB displacement immediate
" f7 f9 \n" // multiply EAX by ECX
// ModR/M in binary: 11 (direct mode) 111 (subop idiv) 001 (divisor ECX)
);
CHECK_TRACE_CONTENTS(
"run: operate on r/m32\n"
"run: r/m32 is ECX\n"
"run: subop: divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX\n"
"run: quotient: 0xfffffffe\n" // -2
"run: remainder: 0xffffffff\n" // -1, same sign as divident (EDX:EAX)
);
}
void test_divide_negative_edx_eax_by_rm32() {
Reg[EAX].i = 0; // lower 32 bits are clear
Reg[EDX].i = -7;
Reg[ECX].i = 0x40000000; // 2^30 (largest positive power of 2)
run(
"== 0x1\n" // code segment
// op ModR/M SIB displacement immediate
" f7 f9 \n" // multiply EAX by ECX
// ModR/M in binary: 11 (direct mode) 111 (subop idiv) 001 (divisor ECX)
);
CHECK_TRACE_CONTENTS(
"run: operate on r/m32\n"
"run: r/m32 is ECX\n"
"run: subop: divide EDX:EAX by r/m32, storing quotient in EAX and remainder in EDX\n"
"run: quotient: 0xffffffe4\n" // (-7 << 32) / (1 << 30) = -7 << 2 = -28
"run: remainder: 0x00000000\n"
);
}
//:: shift left
:(before "End Initialize Op Names")

2
subx/opcodes
View File

@ -82,7 +82,7 @@ Opcodes currently supported by SubX:
e9: jump disp32 bytes away (jmp)
eb: jump disp8 bytes away (jmp)
f4: halt (hlt)
f7: negate/multiply rm32 (with EAX if necessary) depending on subop (neg/mul)
f7: negate/multiply/divide rm32 (with EAX and EDX if necessary) depending on subop (neg/mul/idiv)
ff: increment/decrement/jump/push/call rm32 based on subop (inc/dec/jmp/push/call)
0f 84: jump disp32 bytes away if equal, if ZF is set (jcc/jz/je)
0f 85: jump disp32 bytes away if not equal, if ZF is not set (jcc/jnz/jne)