QSUB Saturating Subtract Saturating Subtract subtracts one register value from another register value, saturates the result to the 32-bit signed integer range -2³¹ <= x <= 2³¹ - 1, and writes the result to the destination register. If saturation occurs, it sets PSTATE.Q to 1. For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors. It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) . != 1111 0 0 0 1 0 0 1 0 (0) (0) (0) (0) 0 1 0 1 QSUB{<c>}{<q>} {<Rd>,} <Rm>, <Rn> d = UInt(Rd); n = UInt(Rn); m = UInt(Rm); if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; 1 1 1 1 1 0 1 0 1 0 0 0 1 1 1 1 1 0 1 0 QSUB{<c>}{<q>} {<Rd>,} <Rm>, <Rn> d = UInt(Rd); n = UInt(Rn); m = UInt(Rm); if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13 <c> See Standard assembler syntax fields. <q> See Standard assembler syntax fields. <Rd> Is the general-purpose destination register, encoded in the "Rd" field. <Rm> Is the first general-purpose source register, encoded in the "Rm" field. <Rn> Is the second general-purpose source register, encoded in the "Rn" field. if ConditionPassed() then EncodingSpecificOperations(); boolean sat; (R[d], sat) = SignedSatQ(SInt(R[m]) - SInt(R[n]), 32); if sat then PSTATE.Q = '1';