Lambda Functions for Segment Sort Operations

Table of Contents

• Fetch Lambda
• Compare Lambda
• Swap Lambda
• Condition Lambda

This page describes the lambda function signatures used in segment sort operations.

Fetch Lambda

The fetch lambda retrieves the value of an element for comparison during sorting. It has one of the following forms:

Full form:

auto fetch = [=] __cuda_callable__ ( IndexType segmentIdx, IndexType localIdx, IndexType globalIdx )
{
   // Return the value at the given position
   return ...;
};

Brief form:

auto fetch = [=] __cuda_callable__ ( IndexType globalIdx )
{
   // Return the value at the given position
   return ...;
};

In both variants:

• segmentIdx is the index of the segment.
• localIdx is the rank of the element within the segment.
• globalIdx is the index of the element in the corresponding container.

Compare Lambda

The compare lambda determines the ordering of two elements during sorting. It has the following signature:

auto compare = [=] __cuda_callable__ ( ValueType a, ValueType b ) -> bool
{
   // Return true if a should come before or equal to b
   return a <= b;
};

The lambda should return true if a should come before or be equal to b in the sorted order.

Swap Lambda

The swap lambda exchanges two elements during the sorting process. It has the following signature:

auto swap = [=] __cuda_callable__ ( IndexType globalIdx1, IndexType globalIdx2 )
{
   // Swap elements at positions globalIdx1 and globalIdx2
   ...
};

• globalIdx1 is the index of the first element to swap.
• globalIdx2 is the index of the second element to swap.

Condition Lambda

The condition lambda determines which segments should be sorted. It has the following signature:

auto condition = [=] __cuda_callable__ ( IndexType segmentIdx ) -> bool
{
   // Return true if segment should be sorted
   return ...;
};

• segmentIdx is the index of the segment.

The lambda should return true if the segment should be sorted.