__rdtscp
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__rdtscp

Microsoft Specific

Generates the rdtscp instruction, writes TSC_AUX[31:0] to memory, and returns the 64-bit Time Stamp Counter (TSC) result.

unsigned __int64 __rdtscp(
   unsigned int * Aux
);

[out] Aux

Pointer to a location that will contain the contents of the machine-specific register TSC_AUX[31:0].

A 64-bit unsigned integer tick count.

Intrinsic

Architecture

__rdtscp

AMD NPT Family 0Fh or later versions

Header file <intrin.h>

This intrinsic generates the rdtscp instruction. To determine hardware support for this instruction, call the __cpuid intrinsic with InfoType=0x80000001 and check bit 27 of CPUInfo[3] (EDX). This bit is 1 if the instruction is supported, and 0 otherwise. If you run code that uses this intrinsic on hardware that does not support the rdtscp instruction, the results are unpredictable.

Caution noteCaution

Unlike rdtsc, rdtscp is a serializing instruction; nevertheless, the compiler can move code around this intrinsic.

The interpretation of the TSC value in this generation of hardware differs from that in earlier versions of x64. See hardware manuals for more information.

The meaning of the value in TSC_AUX[31:0] depends on the operating system.

#include <intrin.h> 
#include <stdio.h>
int main() 
{
 unsigned __int64 i;
 unsigned int ui;
 i = __rdtscp(&ui);
 printf_s("%I64d ticks\n", i);
 printf_s("TSC_AUX was %x\n", ui);
}
3363423610155519 ticks
TSC_AUX was 0

Copyright 2007 by Advanced Micro Devices, Inc. All rights reserved. Reproduced with permission from Advanced Micro Devices, Inc.

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