USAT -- AArch32

USAT

Unsigned Saturate saturates an optionally-shifted signed value to a selected unsigned range.

This instruction sets PSTATE.Q to 1 if the operation saturates.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1

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
!= 1111				0	1	1	0	1	1	1	sat_imm					Rd				imm5					sh	0	1	Rn
cond

Arithmetic shift right (sh == 1)

USAT{<c>}{<q>} <Rd>, #<imm>, <Rn>, ASR #<amount>

Logical shift left (sh == 0)

USAT{<c>}{<q>} <Rd>, #<imm>, <Rn> {, LSL #<amount>}

constant d = UInt(Rd); constant n = UInt(Rn); constant saturate_to = UInt(sat_imm); constant (shift_t, shift_n) = DecodeImmShift(sh:'0', imm5); if d == 15 || n == 15 then UNPREDICTABLE;

T1

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
1	1	1	1	0	(0)	1	1	1	0	sh	0	Rn				0	imm3			Rd				imm2		(0)	sat_imm

Arithmetic shift right (sh == 1 && !(imm3 == 000 && imm2 == 00))

USAT{<c>}{<q>} <Rd>, #<imm>, <Rn>, ASR #<amount>

Logical shift left (sh == 0)

USAT{<c>}{<q>} <Rd>, #<imm>, <Rn> {, LSL #<amount>}

if sh == '1' && (imm3:imm2) == '00000' then SEE "USAT16"; constant d = UInt(Rd); constant n = UInt(Rn); constant saturate_to = UInt(sat_imm); constant (shift_t, shift_n) = DecodeImmShift(sh:'0', imm3:imm2); // Armv8-A removes UNPREDICTABLE for R13 if d == 15 || n == 15 then UNPREDICTABLE;

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>	See Standard assembler syntax fields.

<q>	See Standard assembler syntax fields.

<Rd>	Is the general-purpose destination register, encoded in the "Rd" field.

<imm>

Is the bit position for saturation, in the range 0 to 31, encoded in the "sat_imm" field.

<Rn>	Is the general-purpose source register, encoded in the "Rn" field.

<amount>	For encoding A1: is the optional shift amount, in the range 0 to 31, defaulting to 0 and encoded in the "imm5" field.
	For encoding A1: is the shift amount, in the range 1 to 32 encoded in the "imm5" field as <amount> modulo 32.
	For encoding T1: is the optional shift amount, in the range 0 to 31, defaulting to 0 and encoded in the "imm3:imm2" field.
	For encoding T1: is the shift amount, in the range 1 to 31 encoded in the "imm3:imm2" field as <amount>.

Operation

if ConditionPassed() then EncodingSpecificOperations(); constant operand = Shift(R[n], shift_t, shift_n, PSTATE.C); // PSTATE.C ignored constant (result, sat) = UnsignedSatQ(SInt(operand), saturate_to); R[d] = ZeroExtend(result, 32); if sat then PSTATE.Q = '1';

Internal version only: isa v01_31, pseudocode v2024-03_rel ; Build timestamp: 2024-03-25T10:05