ARMv8指令学习(2)

1. UXTB —- Unsigned extend byte

UXTB , 等同于 UBFM ,,#0,#7

即：Wd = ZeroExtend(Wn<7:0>)

从Wn中取出一个byte，赋给Wd，并把Wd的高3 bytes，用0填充。

2. UXTH —- Unsigned extend halfword

UXTB , 等同于 UBFM ,,#0,#15

即：Wd = ZeroExtend(Wn<15:0>)

从Wn中取出2个byte，赋给Wd，并把Wd的高2 bytes，用0填充。

3. Bitfield move指令
(1) BFM : Bitfield move

BFM Wd,Wn,#r,#s

if (s>=r )

Wd = Wn

else

Wd<32+s-r,32-r> = Wn

一起：坚持Wd中的其它bit不变
(2)SBFM: Signed bitfield move

SBFM Wd,Wn,#r,#s

if (s>=r )

Wd = Wn

else

Wd<32+s-r,32-r> = Wn

并扩展相应的符号位.

(3)UBFM:Unsignedbitfield move

UBFM Wd,Wn,#r,#s

if (s>=r )

Wd = Wn

else

Wd<32+s-r,32-r> = Wn

一起：设置Wd中的其它bit位为0

4. Bitfield insert and extract指令
(1) BFI : Bitfield insert

BFI Wd, Wn, #lsb, #width

等同于

BFM Wd, Wn, #((32-lsb)&31) , #(width-1)

即：

width bits in Wd , starting at lsb , are replaced by width bits from Wn, starting at bit[0].

Other bits in Rd are unchanged

BFI指令，不会更改PSTATE中的flags

(2) BFXIL : Bitfield extract and insert low

BFXIL Wd, Wn, #lsb, #width
等同于
BFM Wd,Wn,#lsb,#(lsb+width-1)

(3) SBFIZ : Signed bitfield insert in zero
(4) SBFX : Signed bitfield extract
(5) UBFIZ : Unsigned bitfield insert in zero
(6) UBFX : Unsigned bitfield extract