RealView® Compilation Tools Assembler Guide 4.3.10. SEL

4.3.10. SEL

Select bytes from each operand according to the state of the CPSR GE flags.

Syntax

SEL{cond} Rd, Rn, Rm

where:

cond: is an optional condition code (see Conditional execution).
Rd: is the destination register.
Rn: is the register holding the first operand.
Rm: is the register holding the second operand.

Operation

The SEL instruction selects bytes from Rn or Rm according to the CPSR GE flags:

if GE[0] is set, Rd[7:0] come from Rn[7:0], otherwise from Rm[7:0]
if GE[1] is set, Rd[15:8] come from Rn[15:8], otherwise from Rm[15:8]
if GE[2] is set, Rd[23:16] come from Rn[23:16], otherwise from Rm[23:16]
if GE[3] is set, Rd[31:24] come from Rn[31:24], otherwise from Rm[31:24].

Usage

Do not use r15 for Rd, Rn, or Rm.

Use the SEL instruction after one of the signed parallel instructions, see Parallel add and subtract. You can use this to select maximum or minimum values in multiple byte or halfword data.

Condition flags

This instruction does not change the flags.

Architectures

This ARM instruction is available in ARMv6 and above.

This 32-bit Thumb-2 instruction is available in T2 variants of ARMv6 and above.

There is no 16-bit Thumb version of this instruction.

Examples

    SEL     r0, r4, r5
    SELLT   r4, r0, r4

The following instruction sequence sets each byte in r4 equal to the unsigned minimum of the corresponding bytes of r1 and r2:

    USUB8    r4, r1, r2
    SEL      r4, r2, r1

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