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UserspaceEmulator: Make SBB actually respect the SoftCPU carry flag

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We were forgetting to set the host CPU's carry flag before executing
the SBB instruction. This made the result a bit unpredictable. :^)
This commit is contained in:
Andreas Kling 2020-07-13 13:31:51 +02:00
parent a9f92e5d75
commit 6230c60296
1 changed files with 15 additions and 2 deletions
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17
DevTools/UserspaceEmulator/SoftCPU.cpp
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@ -343,12 +343,17 @@ static T op_sub(SoftCPU& cpu, const T& dest, const T& src)
return result; return result;
} }
template<typename T> template<typename T, bool cf>
static T op_sbb(SoftCPU& cpu, const T& dest, const T& src) static T op_sbb_impl(SoftCPU& cpu, const T& dest, const T& src)
{ {
T result = 0; T result = 0;
u32 new_flags = 0; u32 new_flags = 0;
if constexpr (cf)
asm volatile("stc");
else
asm volatile("clc");
if constexpr (sizeof(T) == 4) { if constexpr (sizeof(T) == 4) {
asm volatile("sbbl %%ecx, %%eax\n" asm volatile("sbbl %%ecx, %%eax\n"
: "=a"(result) : "=a"(result)
@ -374,6 +379,14 @@ static T op_sbb(SoftCPU& cpu, const T& dest, const T& src)
return result; return result;
} }
template<typename T>
static T op_sbb(SoftCPU& cpu, T& dest, const T& src)
{
if (cpu.cf())
return op_sbb_impl<T, true>(cpu, dest, src);
return op_sbb_impl<T, false>(cpu, dest, src);
}
template<typename T> template<typename T>
static T op_add(SoftCPU& cpu, T& dest, const T& src) static T op_add(SoftCPU& cpu, T& dest, const T& src)
{ {