C ++如何转换向量 <uint8_t> 大小4变成32位浮点数

Question

What is the fastest way to convert a vector of size 4 into a 32 bit float?

My failed attempt:

static bool vec2float32(std::vector<uint8_t> bytes, float &result)
{
    if(bytes.size() != 4) return false;
    uint8_t sign = (bytes.at(0) & 0x10000000); //will be 1 or 0
    uint8_t exponent = (bytes.at(0) & 0x01111111);
    uint16_t mantissa = (bytes.at(1) << (2*8)) + (bytes.at(2) << (1*8)) + (bytes.at(3) << (0*8));

    result = (2^(exponent - 127)) * mantissa;
    if(sign == 1) result = result * -1;
    return true;
}

Answer 1

I believe this should be the fastest:

return *reinterpret_cast<float*>(&bytes[0]);

I think its technically undefined behavior. But most compilers should output what you expect here. The &bytes[0] is guaranteed to work because std::vector is guaranteed to be contiguous.

Answer 2

From the vector you can get a pointer to the first byte. If the bytes are already in the correct order, then you can copy the bytes directly into a float variable.