CODEWITHSUNDEEP
c++floating-pointx86-64
jeffreyveon
jeffreyveon

Reputation: 13830

Convert float to int64_t while preserving ordering

My question is similar to this question which deals with positive floating point values.

In my case, I'm dealing with both positive and negative float values, and want to store it in an int64_t type.

NOTE: I wish to use memcpy rather than relying on a union (which is UB in C++).

Upvotes: 1

Views: 540

Answers (1)

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215287

As described in my comment on the linked question about a 32-bit variant:

...basically you can either use a signed int32 and invert the low 31 bits if the sign bit is set. A similar approach works if you want unsigned but you have to add the 0x80000000 bias.

As code, adapted to 64-bit:

int64_t order_preserving_repr(double x)
{
    int64_t k;
    memcpy(&k, &x, sizeof k);
    if (k<0) k ^= INT64_MAX;
    return k;
}

Upvotes: 2

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