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## RSUBHNB

Rounding subtract narrow high part (bottom).

Subtract each vector element of the second source vector from the corresponding vector element in the first source vector, and place the most significant rounded half of the result in the even-numbered half-width destination elements, while setting the odd-numbered half-width destination elements to zero. This instruction is unpredicated.

 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 size 1 Zm 0 1 1 1 1 0 Zn Zd S R T
```if !HaveSVE2() then UNDEFINED;
if size == '00' then UNDEFINED;
integer esize = 8 << UInt(size);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer d = UInt(Zd);```

### Assembler Symbols

 Is the name of the destination scalable vector register, encoded in the "Zd" field.
<T> Is the size specifier, encoded in size:
size <T>
00 RESERVED
01 B
10 H
11 S
 Is the name of the first source scalable vector register, encoded in the "Zn" field.
<Tb> Is the size specifier, encoded in size:
size <Tb>
00 RESERVED
01 H
10 S
11 D
 Is the name of the second source scalable vector register, encoded in the "Zm" field.

### Operation

```CheckSVEEnabled();
integer elements = VL DIV esize;
bits(VL) operand1 = Z[n];
bits(VL) operand2 = Z[m];
bits(VL) result;
integer halfesize = esize DIV 2;
integer round_const = 1 << (halfesize - 1);

for e = 0 to elements-1
integer element1 = UInt(Elem[operand1, e, esize]);
integer element2 = UInt(Elem[operand2, e, esize]);
integer res = ((element1 - element2) + round_const) >> halfesize;
Elem[result, 2*e + 0, halfesize] = res<halfesize-1:0>;
Elem[result, 2*e + 1, halfesize] = Zeros();

Z[d] = result;```

### Operational information

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.