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Remove undefined behavior from shifts

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`asl` and `asr` in `src/link/patch.c` courtesy of @pinobatch, and rearranged in RGBASM
evaluators.
This commit is contained in:
ISSOtm
2020-01-17 09:08:49 +01:00
parent 1bd41bf79a
commit b11d121c48
10 changed files with 244 additions and 37 deletions
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60
src/asm/rpn.c
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@@ -409,22 +409,59 @@ void rpn_AND(struct Expression *expr, const struct Expression *src1,
expr->nRPNPatchSize++;
}
static int32_t shift(int32_t shiftee, int32_t amount)
{
if (shiftee < 0)
warning(WARNING_SHIFT, "Shifting negative value %d", shiftee);
if (amount >= 0) {
// Left shift
if (amount >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting left by large amount %d",
amount);
return 0;
} else {
/*
* Use unsigned to force a bitwise shift
* Casting back is OK because the types implement two's
* complement behavior
*/
return (uint32_t)shiftee << amount;
}
} else {
// Right shift
amount = -amount;
if (amount >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting right by large amount %d",
amount);
return shiftee < 0 ? -1 : 0;
} else if (shiftee >= 0) {
return shiftee >> amount;
} else {
/*
* The C standard leaves shifting right negative values
* undefined, so use a left shift manually sign-extended
*/
return (uint32_t)shiftee >> amount
| -((uint32_t)1 << (32 - amount));
}
}
}
void rpn_SHL(struct Expression *expr, const struct Expression *src1,
const struct Expression *src2)
{
mergetwoexpressions(expr, src1, src2);
if (!expr->isReloc) {
if (src1->nVal < 0)
warning(WARNING_SHIFT, "Left shift of negative value: %d",
src1->nVal);
if (src2->nVal < 0)
fatalerror("Shift by negative value: %d", src2->nVal);
else if (src2->nVal >= 32)
fatalerror("Shift by too big value: %d", src2->nVal);
warning(WARNING_SHIFT_AMOUNT, "Shifting left by negative value: %d",
src2->nVal);
expr->nVal = ((uint32_t)src1->nVal << src2->nVal);
expr->nVal = shift(src1->nVal, src2->nVal);
}
pushbyte(expr, RPN_SHL);
@@ -438,11 +475,10 @@ void rpn_SHR(struct Expression *expr, const struct Expression *src1,
if (!expr->isReloc) {
if (src2->nVal < 0)
fatalerror("Shift by negative value: %d", src2->nVal);
else if (src2->nVal >= 32)
fatalerror("Shift by too big value: %d", src2->nVal);
warning(WARNING_SHIFT_AMOUNT, "Shifting right by negative value: %d",
src2->nVal);
expr->nVal = (src1->nVal >> src2->nVal);
expr->nVal = shift(src1->nVal, -src2->nVal);
}
pushbyte(expr, RPN_SHR);