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#pragma [no_]anon_unions

#pragma arm section [section_sort_list]

#pragma diag_default tag[,tag,...]

#pragma diag_error tag[,tag,...]

#pragma diag_remark tag[,tag,...]

#pragma diag_suppress tag[,tag,...]

#pragma diag_warning tag[, tag, ...]

#pragma [no_]exceptions_unwind

#pragma hdrstop

#pragma import symbol_name

#pragma [no_]inline

#pragma [no_]softfp_linkage

#pragma unroll [(n)]

#pragma unroll_completely

Instruction intrinsics

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__return_address

__schedule_barrier

__swp

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__swp

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Version 3.1

Home > Compiler-specific Features > Instruction intrinsics > __swp

4.7.41. `__swp`

This intrinsic inserts a SWP{size} instruction into the instruction stream generated by the compiler. It enables you to swap data between memory locations from your C or C++ code.

Note

The use of SWP and SWPB is deprecated in ARMv6 and above.

Syntax

unsigned int __swp(unsigned int val, volatile void *ptr)

where:

val

Is the data value to be written to memory.

ptr

Points to the address of the data to be written to in memory. To specify the size of the data to be written, cast the parameter to an appropriate integral type.

Table 4.12. Access widths supported by the __swp intrinsic

Instruction	Size of data loaded	C cast
`SWPB`	unsigned byte	`(`char `*)`
`SWP`	word	`(`int `*)`

Return value

The __swp intrinsic returns the data value that previously, is in the memory address pointed to by ptr, before this value is overwitten by val.

Example

int foo(void)
{
    int loc=0xff;
    return(__swp(0x20, (volatile int *)loc));
}

Compiling this code produces

||foo|| PROC
    MOV      r1, #0xff
    MOV      r0, #0x20
    SWP      r0, r0, [r1]
    BX       lr
    ENDP

See also

SWP and SWPB in the Assembler Guide.

Copyright © 2007 ARM Limited. All rights reserved.	ARM DUI 0376A
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