Fast conversion of 16-bit big-endian to little-endian in ARM

I need to convert big arrays of 16-bit integer values from big-endian to little-endian format.

Now I use for conversion the following function:

inline void Reorder16bit(const uint8_t * src, uint8_t * dst)
{
    uint16_t value = *(uint16_t*)src;
    *(uint16_t*)dst = value >> 8 | value << 8;
}

void Reorder16bit(const uint8_t * src, size_t size, uint8_t * dst)
{
    assert(size%2 == 0);
    for(size_t i = 0; i < size; i += 2)
        Reorder16bit(src + i, dst + i);
}

I use GCC. Target platform is ARMv7 (Raspberry Phi 2B).

Is there any way to optimize it?

This conversion is needed for loading audio samples which can be as in little- endian as in big-endian format. Of course it is not a bottleneck now, but it takes about 10% of total processing time. And I think that is too much for such a simple operation.

If you want to improve performance of your code you can make following:

1) Processing of 4-bytes for one step:

inline void Reorder16bit(const uint8_t * src, uint8_t * dst)
{
    uint16_t value = *(uint16_t*)src;
    *(uint16_t*)dst = value >> 8 | value << 8;
}

inline void Reorder16bit2(const uint8_t * src, uint8_t * dst)
{
    uint32_t value = *(uint32_t*)src;
    *(size_t*)dst = (value & 0xFF00FF00) >> 8 | (value & 0x00FF00FF) << 8;
}

void Reorder16bit(const uint8_t * src, size_t size, uint8_t * dst)
{
    assert(size%2 == 0);

    size_t alignedSize = size/4*4;
    for(size_t i = 0; i < alignedSize; i += 4)
        Reorder16bit2(src + i, dst + i);
    for(size_t i = alignedSize; i < size; i += 2)
        Reorder16bit(src + i, dst + i);
}

If you use a 64-bit platform, it is possible to process 8 bytes for one step the same way.

2) ARMv7 platform supports SIMD instructions called NEON. With using of them you can make you code even faster then in 1):

inline void Reorder16bit(const uint8_t * src, uint8_t * dst)
{
    uint16_t value = *(uint16_t*)src;
    *(uint16_t*)dst = value >> 8 | value << 8;
}

inline void Reorder16bit8(const uint8_t * src, uint8_t * dst)
{
    uint8x16_t _src = vld1q_u8(src);
    vst1q_u8(dst, vrev16q_u8(_src));
}

void Reorder16bit(const uint8_t * src, size_t size, uint8_t * dst)
{
    assert(size%2 == 0);

    size_t alignedSize = size/16*16;
    for(size_t i = 0; i < alignedSize; i += 16)
        Reorder16bit8(src + i, dst + i);
    for(size_t i = alignedSize; i < size; i += 2)
        Reorder16bit(src + i, dst + i);
}