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__strex intrinsic

This intrinsic inserts an instruction of the form STREX[size] into the instruction stream generated by the compiler. It enables you to use an STREX instruction in your C or C++ code to store data to memory.


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



is the value to be written to memory.


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 18. Access widths supported by the __strex intrinsic
InstructionSize of data storedC cast
STREXBunsigned byte(char *)
STREXHunsigned halfword(short *)
STREXword(int *)

Return value

The __strex intrinsic returns:


if the STREX instruction succeeds


if the STREX instruction is locked out.


The compiler does not recognize the __strex intrinsic when compiling for a target that does not support the STREX instruction. The compiler generates either a warning or an error in this case.

The __strex intrinsic does not support access to doubleword data. The compiler generates an error if you specify an access width that is not supported.


int foo(void)
    int loc=0xff;
    return(!__strex(0x20, (volatile char *)loc));

Compiling this code with the command-line option --cpu=6k produces

||foo|| PROC
    MOV      r0,#0xff
    MOV      r2,#0x20
    STREXB   r1,r2,[r0]
    RSBS     r0,r1,#1
    MOVCC    r0,#0
    BX       lr