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/*
* Copyright (c) 2018-2019, NVIDIA CORPORATION. All rights reserved.
*
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include <stdint.h>
struct TimestampConverter
{
int64_t dstAtSyncPoint;
int64_t srcAtSyncPoint;
double scale;
int64_t operator()(int64_t srcTimestamp) const
{
auto srcDelta = srcTimestamp - srcAtSyncPoint;
auto dstDelta = static_cast<int64_t>(scale * static_cast<double>(srcDelta));
return dstDelta + dstAtSyncPoint;
}
};
inline TimestampConverter CreateTimestampConverter(
int64_t srcStart,
int64_t srcEnd,
int64_t dstStart,
int64_t dstEnd)
{
auto dstDelta = dstEnd - dstStart;
auto srcDelta = srcEnd - srcStart;
double scale = (srcDelta == 0.0) ? 0.0 :
(static_cast<double>(dstDelta) / static_cast<double>(srcDelta));
// Any sync point can be used for conversions. Since we are subtracting the
// sync point from each timestamp before scaling it, the 53-bit mantissa of
// double makes our scaling precision about 1 nanosecond per week of distance
// from the sync point (assuming 1 GHz clocks). So, accuracy is best near
// the sync point, samples one week later could be off by 1ns, samples two
// weeks later by 2ns, etc. For short captures the choice of sync point is
// irrelevant, but in a snapshot-based tool where the region of interest is
// nearer to the end, we should prioritize accuracy at the end highest, so we
// select the end of capture as our sync point.
return {dstEnd, srcEnd, scale};
}
// Helper functions for common timestamp-conversion cases:
// - Converting CPU ticks to nanoseconds
// - Creating a new converter that is the reverse of an existing one
// - Creating a new converter that is the composition two existing ones
inline TimestampConverter CpuToNsTimestampConverter(
int64_t cpuTimestampTicksPerSecond,
int64_t cpuTimestampStart)
{
// Source is CPU timestamps, destination is nanoseconds since cpuTimestampStart
double nsPerCpuTimestampTick =
static_cast<double>(1'000'000'000) / static_cast<double>(cpuTimestampTicksPerSecond);
return {0, cpuTimestampStart, nsPerCpuTimestampTick};
}
inline TimestampConverter ReverseConverter(
TimestampConverter const& in)
{
// Swap dst & src offsets, and invert scale
return {in.srcAtSyncPoint, in.dstAtSyncPoint, 1.0 / in.scale};
}
inline TimestampConverter ComposeConverters(
TimestampConverter const& ab,
TimestampConverter const& bc)
{
// ConvAtoB(a) = (a - abSrc) * abScale + abDst
// ConvBtoC(b) = (b - bcSrc) * bcScale + bcDst
// So, replacing b in ConvBtoC with ConvAtoB(a), we define ConvAtoC(a):
// = (((a - abSrc) * abScale + abDst) - bcSrc) * bcScale + bcDst
// = ((a - abSrc) * abScale + (abDst - bcSrc)) * bcScale + bcDst
// = (a - abSrc) * abScale * bcScale + (abDst - bcSrc) * bcScale + bcDst
// ...which fits the form (a - acSrc) * acScale + acDst, using:
// acScale = abScale * bcScale
// acSrc = abSrc
// acDst = bcDst + (abDst - bcSrc) * bcScale
int64_t acSrc = ab.srcAtSyncPoint;
int64_t acDst = bc.dstAtSyncPoint +
static_cast<int64_t>(static_cast<double>(ab.dstAtSyncPoint - bc.srcAtSyncPoint) * bc.scale);
return {acDst, acSrc, ab.scale * bc.scale};
}
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