LSLV

Logical shift left variable

This instruction shifts a register value left by a variable number of bits, shifting in zeros, and writes the result to the destination register. The value of the second source register modulo the register size in bits gives the number of bits by which the first source register is left-shifted.

Encoding: Integer

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
	0	0	1	1	0	1	0	1	1	0						0	0	1	0	0	0
sf		S									Rm									op2		Rn					Rd

32-bit (sf == 0)

LSLV <Wd>, <Wn>, <Wm>

64-bit (sf == 1)

LSLV <Xd>, <Xn>, <Xm>

Decoding algorithm

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer datasize = 32 << UInt(sf);
constant ShiftType shift_type = DecodeShift(op2);

Operation

constant bits(datasize) operand2 = X[m, datasize];

X[d, datasize] = ShiftReg(n, shift_type, UInt(operand2) MOD datasize, datasize);

Explanations

<Wd>: Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Wn>: Is the 32-bit name of the first general-purpose source register, encoded in the "Rn" field.
<Wm>: Is the 32-bit name of the second general-purpose source register holding a shift amount from 0 to 31 in its bottom 5 bits, encoded in the "Rm" field.
<Xd>: Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Xn>: Is the 64-bit name of the first general-purpose source register, encoded in the "Rn" field.
<Xm>: Is the 64-bit name of the second general-purpose source register holding a shift amount from 0 to 63 in its bottom 6 bits, encoded in the "Rm" field.

Operational Notes

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.