SQSHRN, SQSHRN2
Signed saturating Shift Right Narrow (immediate). This instruction reads each vector element in the source SIMD&FP register, right shifts and truncates each result by an immediate value, saturates each shifted result to a value that is half the original width, puts the final result into a vector, and writes the vector to the lower or upper half of the destination SIMD&FP register. All the values in this instruction are signed integer values. The destination vector elements are half as long as the source vector elements. For rounded results, see SQRSHRN.
The SQSHRN instruction writes the vector to the lower half of the destination register and clears the upper half, while the SQSHRN2 instruction writes the vector to the upper half of the destination register without affecting the other bits of the register.
If saturation occurs, the cumulative saturation bit FPSR.QC is set.
Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.
It has encodings from 2 classes:
Scalar
and
Vector
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 | 1 | 1 | 1 | 1 | 1 | 0 | != 0000 | immb | 1 | 0 | 0 | 1 | 0 | 1 | Rn | Rd |
| U | | immh | | | op | | | |
integer d = UInt(Rd);
integer n = UInt(Rn);
if immh == '0000' then ReservedValue();
if immh<3> == '1' then ReservedValue();
integer esize = 8 << HighestSetBit(immh);
integer datasize = esize;
integer elements = 1;
integer part = 0;
integer shift = (2 * esize) - UInt(immh:immb);
boolean round = (op == '1');
boolean unsigned = (U == '1');
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 | Q | 0 | 0 | 1 | 1 | 1 | 1 | 0 | != 0000 | immb | 1 | 0 | 0 | 1 | 0 | 1 | Rn | Rd |
| | U | | immh | | | op | | | |
integer d = UInt(Rd);
integer n = UInt(Rn);
if immh == '0000' then SEE(asimdimm);
if immh<3> == '1' then ReservedValue();
integer esize = 8 << HighestSetBit(immh);
integer datasize = 64;
integer part = UInt(Q);
integer elements = datasize DIV esize;
integer shift = (2 * esize) - UInt(immh:immb);
boolean round = (op == '1');
boolean unsigned = (U == '1');
Assembler Symbols
Operation
CheckFPAdvSIMDEnabled64();
bits(datasize*2) operand = V[n];
bits(datasize) result;
integer round_const = if round then (1 << (shift - 1)) else 0;
integer element;
boolean sat;
for e = 0 to elements-1
element = (Int(Elem[operand, e, 2*esize], unsigned) + round_const) >> shift;
(Elem[result, e, esize], sat) = SatQ(element, esize, unsigned);
if sat then FPSR.QC = '1';
Vpart[d, part] = result;
Internal version only: isa v25.07, AdvSIMD v23.0, pseudocode v31.3
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