SHRNB

Shift right narrow by immediate (bottom)

Shift each unsigned integer value in the source vector elements right by an immediate value, and place the truncated results in the even-numbered half-width destination elements, while setting the odd-numbered elements to zero. The immediate shift amount is an unsigned value in the range 1 to number of bits per element. This instruction is unpredicated.

Encoding: SVE2

Variants: FEAT_SVE2 || FEAT_SME (FEAT_SVE2 || FEAT_SME)

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	1	0	0	0	1	0	1	0		1						0	0	0	1	0	0
									tszh		tszl		imm3					op	U	R	T	Zn					Zd

SHRNB <Zd>.<T>, <Zn>.<Tb>, #<const>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant bits(3) tsize = tszh:tszl;
if tsize == '000' then EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << HighestSetBit(tsize);
constant integer n = UInt(Zn);
constant integer d = UInt(Zd);
constant integer shift = (2 * esize) - UInt(tsize:imm3);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer elements = VL DIV (2 * esize);
constant bits(VL) operand = Z[n, VL];
bits(VL) result;
for e = 0 to elements-1
    constant bits(2*esize) element = Elem[operand, e, 2*esize];
    constant integer res = UInt(element) >> shift;
    Elem[result, 2*e + 0, esize] = res;
    Elem[result, 2*e + 1, esize] = Zeros(esize);

Z[d, VL] = result;

Explanations

<Zd>: Is the name of the destination scalable vector register, encoded in the "Zd" field.
<T>: <Zn>: Is the name of the source scalable vector register, encoded in the "Zn" field.
<Tb>: <const>: Is the immediate shift amount, in the range 1 to number of bits per element, encoded in "tszh:tszl:imm3".

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.