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replace if-s in AArch64_AM_decodeAdvSIMDModImmType10 with lookup table (#552)

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* replace if-s in AArch64_AM_decodeAdvSIMDModImmType10 with lookup table

Lookup table is much faster than bunch of if-s. If you don't like lookup tables, I have another proposal. See http://goo.gl/RjW1lr and compare generated machine code

* Smaller lookup table and shifting and bit mask used

* Update AArch64AddressingModes.h
This commit is contained in:
szt
2017-04-15 04:50:06 +03:00
committed by Nguyen Anh Quynh
parent e3ff166781
commit 8e39d82841
1 changed files with 7 additions and 10 deletions
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17
arch/AArch64/AArch64AddressingModes.h
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@ -213,16 +213,13 @@ static inline float AArch64_AM_getFPImmFloat(unsigned Imm)
static inline uint64_t AArch64_AM_decodeAdvSIMDModImmType10(uint8_t Imm)
{
uint64_t EncVal = 0;
if (Imm & 0x80) EncVal |= 0xff00000000000000ULL;
if (Imm & 0x40) EncVal |= 0x00ff000000000000ULL;
if (Imm & 0x20) EncVal |= 0x0000ff0000000000ULL;
if (Imm & 0x10) EncVal |= 0x000000ff00000000ULL;
if (Imm & 0x08) EncVal |= 0x00000000ff000000ULL;
if (Imm & 0x04) EncVal |= 0x0000000000ff0000ULL;
if (Imm & 0x02) EncVal |= 0x000000000000ff00ULL;
if (Imm & 0x01) EncVal |= 0x00000000000000ffULL;
return EncVal;
static const uint32_t lookup[16] = {
0x00000000, 0x000000ff, 0x0000ff00, 0x0000ffff,
0x00ff0000, 0x00ff00ff, 0x00ffff00, 0x00ffffff,
0xff000000, 0xff0000ff, 0xff00ff00, 0xff00ffff,
0xffff0000, 0xffff00ff, 0xffffff00, 0xffffffff
};
return lookup[Imm & 0x0f] | ((uint64_t)lookup[Imm >> 4] << 32);
}
#endif