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c#memorytype-conversionallocation
Sirosimo
Sirosimo

Reputation: 41

Memory<Byte> conversion with minimal or no allocation?

I'm looking to convert a Memory<Byte> to some other type (double, int...) while trying to eliminate allocation (until the final place where the value goes).

I figure out how to get the value of a bit in a byte but I can't seem to figure out how to do it for a double or int. I want to avoid using .ToArray as it would perform a heap allocation.

[EDIT] Also to make things even easier, I need to perform a byte swap prior to conversion.

var buffer = GC.AllocateArray<byte>(1024, true);
var bufferMem = buffer.AsMemory();
//Something put data in bufferMem

var boolValue = bufferMem
    .Slice(0, 1)
    .Span[0]
    .GetBit();


public static bool GetBit(this byte b, int bitIndex)
{
    return (b & (1 << bitIndex)) != 0;
}

Thank you for your help

Upvotes: 1

Views: 449

Answers (1)

Timo
Timo

Reputation: 8700

To work with the elements of a Memory<T>, you normally get a Span<T> from it. That can be interpreted as a span of a different type, provided that T is unmanaged (i.e. recursively does not contain references types).

var buffer = GC.AllocateArray<byte>(1024, true);
var bufferMem = buffer.AsMemory();
//Something put data in bufferMem

var bytes = bufferMem.Span;

// Re-interpret
var doubles = MemoryMarshal.Cast<byte, double>(bytes);

This is allocation-free and highly efficient.

Upvotes: 0

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