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FXCH
Exchanges the contents of a specified floating-point register with the contents of the register at the top of the floating-point register stack (ST(0)).
The following table covers what the source and destinations can be:
| source | destination(s) |
|---|---|
| ST(i) | ST(0) |
DO NOT support LOCK
This instruction is available in both 32-bit and 64-bit modes. It operates exclusively on the x87 floating-point register stack.
The register index $i$ MUST be between 0 and 7. If the specified register is ST(0), the instruction performs no operation. The instruction does not affect the floating-point status word or control word.