Legacy Document

Inside Macintosh: Networking With Open Transport / Part 2 - Open Transport Reference

Chapter 27 - Utilities Reference / Functions

Atomic Operations /

OTCompareAndSwap8

Atomically compares two 8-bit values and changes one of these values if they are the same.

C INTERFACE

Boolean OTCompareAndSwap8(
                     UInt32 oldVal,
                     UInt32 newVal,
                     UInt8* where)

C++ INTERFACE

None. C++ applications use the C interface to this function.

PARAMETERS

oldVal

The 8-bit value being compared to the value referenced by the where parameter.

newVal

The value to be assigned to the 8-bit value referenced by the where parameter.

where

A reference to the 8-bit value being compared to that specified by the oldVal parameter.

function result

Returns true if the swap is done.

DISCUSSION

This function compares the least significant 8 bits of oldVal with the value referenced by the where parameter. If the two values are the same, the function replaces the 8-bit value referenced by the where parameter with the value specified by the newVal parameter and it returns true. If the two values are not the same, no swap occurs and the function returns false.

The entire compare and swap operation is atomic.

Use the OTCompareAndSwap32 function to compare two 32-bit values and set one if they are the same.

Use the OTCompareAndSwap16 function to compare two 16-bit values and set one if they are the same.