[FFmpeg-devel] [PATCH]levc/hevc_cabac Optimise ff_hevc_hls_residual_coding (especially ARM)

[James Almer]

On 1/19/2016 9:46 AM, John Cox wrote:
> +// Helper fns
> +#ifndef hevc_mem_bits32
> +static av_always_inline uint32_t hevc_mem_bits32(const void * buf, const unsigned int offset)
> +{
> +    return AV_RB32((const uint8_t *)buf + (offset >> 3)) << (offset & 7);
> +}
> +#endif
> +
> +#if AV_GCC_VERSION_AT_LEAST(3,4) && !defined(hevc_clz32)
> +#define hevc_clz32 hevc_clz32_builtin
> +static av_always_inline unsigned int hevc_clz32_builtin(const uint32_t x)
> +{
> +    // __builtin_clz says it works on ints - so adjust if int is >32 bits long
> +    return __builtin_clz(x) - (sizeof(int) * 8 - 32);

Why aren't you simply using ff_clz?

> +}
> +#endif
> +
> +// It is unlikely that we will ever need this but include for completeness

There are at least two compilers we support that don't define __GNUC__, so
it would be used.
And in any case, isn't all this duplicating ff_clz, which is available in
libavutil/inthmath.h?

> +#ifndef hevc_clz32
> +static inline unsigned int hevc_clz32(unsigned int x)
> +{
> +    unsigned int n = 1;
> +    if ((x & 0xffff0000) == 0) {
> +        n += 16;
> +        x <<= 16;
> +    }
> +    if ((x & 0xff000000) == 0) {
> +        n += 8;
> +        x <<= 8;
> +    }
> +    if ((x & 0xf0000000) == 0) {
> +        n += 4;
> +        x <<= 4;
> +    }
> +    if ((x & 0xc0000000) == 0) {
> +        n += 2;
> +        x <<= 2;
> +    }
> +    return n - ((x >> 31) & 1);
> +}
> +#endif