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SASX

Signed parallel add and subtract halfwords with exchange.

Syntax

SASX{cond} {Rd}, Rn, Rm

where:

cond

is an optional condition code.

Rd

is the destination register.

Rm, Rn

are the ARM registers holding the operands.

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

You cannot use PC for any operand.

You can use SP in A32 instructions but this is deprecated. You cannot use SP in T32 instructions.

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 a pair of GE flags to 1 to indicate that the corresponding result is greater than or equal to zero. This is equivalent to an ADDS or SUBS instruction setting the N and V condition flags to the same value, so that the GE condition passes.

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

Note

GE[1:0] are set or cleared together, and GE[3:2] are set or cleared together.

Availability

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

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

Related reference

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