11.102 SEL

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

Syntax

SEL{cond} {Rd}, Rn, Rm

where:

cond

is an optional condition code.

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 APSR 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

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

Register restrictions

You cannot use PC for any register.

You can use SP in ARM instructions but this is deprecated in ARMv6T2 and above. You cannot use SP in Thumb instructions.

Condition flags

This instruction does not change the flags.

Architectures

This ARM instruction is available in ARMv6 and above.

This 32-bit Thumb instruction is available in ARMv6T2 and above. For the ARMv7-M architecture, it is only available in an ARMv7E-M implementation.

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

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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