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ARM: Don't rely on undefined behavior to get arithmetic right shift.

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Shifting to the right of a signed value when the MSB is one is technically
undefined behavior, even though in my experience it's done the "right thing"
and sign extended the value. This replaces the arithmetic right shift code in
ARM that uses that coincidence with some code that relies on bit math.
This commit is contained in:
Gabe Black
2010-06-02 12:58:04 -05:00
parent 05d880f7a1
commit 14d25fbad0
1 changed files with 4 additions and 4 deletions
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8
src/arch/arm/insts/static_inst.cc
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@@ -68,9 +68,9 @@ ArmStaticInst::shift_rm_imm(uint32_t base, uint32_t shamt,
return base >> shamt;
case ASR:
if (shamt == 0)
return (int32_t)base >> 31;
return (base >> 31) | -((base & (1 << 31)) >> 31);
else
return (int32_t)base >> shamt;
return (base >> shamt) | -((base & (1 << 31)) >> shamt);
case ROR:
if (shamt == 0)
return (cfval << 31) | (base >> 1); // RRX
@@ -106,9 +106,9 @@ ArmStaticInst::shift_rm_rs(uint32_t base, uint32_t shamt,
return base >> shamt;
case ASR:
if (shamt >= 32)
return (int32_t)base >> 31;
return (base >> 31) | -((base & (1 << 31)) >> 31);
else
return (int32_t)base >> shamt;
return (base >> shamt) | -((base & (1 << 31)) >> shamt);
case ROR:
shamt = shamt & 0x1f;
if (shamt == 0)