Operation

This instruction exchanges the two halfwords of the second operand, then performs an addition on the two top halfwords of the operands and a subtraction on the bottom two halfwords. It writes the results into the corresponding halfwords of the destination. The results are modulo 2¹⁶. It sets the APSR GE flags.

Register restrictions

GE flags

This instruction does not affect the N, Z, C, V, or Q flags.

It sets the GE flags in the APSR as follows:

GE[1:0]

for bits[15:0] of the result.

GE[3:2]

for bits[31:16] of the result.

It sets GE[1:0] to 1 to indicate that the subtraction gave a result greater than or equal to zero, meaning a borrow did not occur. This is equivalent to a SUBS instruction setting the C condition flag to 1.

It sets GE[3:2] to 1 to indicate that the addition overflowed, generating a carry. This is equivalent to an ADDS instruction setting the C condition flag to 1.

You can use these flags to control a following SEL instruction.

Availability

The 32-bit instruction is available in A32 and T32.

For the ARMv7-M architecture, the 32-bit T32 instruction is only available in an ARMv7E-M implementation.

There is no 16-bit version of this instruction in T32.