static unsigned LZ4_NbCommonBytes()

in lib/lz4/lz4.cc [238:316]

• 79 lines of code
• 21 McCabe index (conditional complexity)

static unsigned LZ4_NbCommonBytes(size_t val) {
    if (LZ4_isLittleEndian()) {
        if (LZ4_64bits()) {
#if defined(_MSC_VER) && defined(_WIN64) && !defined(LZ4_FORCE_SW_BITCOUNT)
            unsigned long r = 0;
            _BitScanForward64(&r, (U64)val);
            return (int)(r >> 3);
#elif (defined(__clang__) || (LZ4_GCC_VERSION >= 304)) && !defined(LZ4_FORCE_SW_BITCOUNT)
            return (__builtin_ctzll((U64)val) >> 3);
#else
            static const int DeBruijnBytePos[64] = {0, 0, 0, 0, 0, 1, 1, 2, 0, 3, 1, 3, 1, 4, 2, 7,
                                                    0, 2, 3, 6, 1, 5, 3, 5, 1, 3, 4, 4, 2, 5, 6, 7,
                                                    7, 0, 1, 2, 3, 3, 4, 6, 2, 6, 5, 5, 3, 4, 5, 6,
                                                    7, 1, 2, 4, 6, 4, 4, 5, 7, 2, 6, 5, 7, 6, 7, 7};
            return DeBruijnBytePos[((U64)((val & -(long long)val) * 0x0218A392CDABBD3FULL)) >> 58];
#endif
        } else /* 32 bits */
        {
#if defined(_MSC_VER) && !defined(LZ4_FORCE_SW_BITCOUNT)
            unsigned long r;
            _BitScanForward(&r, (U32)val);
            return (int)(r >> 3);
#elif (defined(__clang__) || (LZ4_GCC_VERSION >= 304)) && !defined(LZ4_FORCE_SW_BITCOUNT)
            return (__builtin_ctz((U32)val) >> 3);
#else
            static const int DeBruijnBytePos[32] = {0, 0, 3, 0, 3, 1, 3, 0, 3, 2, 2, 1, 3, 2, 0, 1,
                                                    3, 3, 1, 2, 2, 2, 2, 0, 3, 1, 2, 0, 1, 0, 1, 1};
            return DeBruijnBytePos[((U32)((val & -(S32)val) * 0x077CB531U)) >> 27];
#endif
        }
    } else /* Big Endian CPU */
    {
        if (LZ4_64bits()) {
#if defined(_MSC_VER) && defined(_WIN64) && !defined(LZ4_FORCE_SW_BITCOUNT)
            unsigned long r = 0;
            _BitScanReverse64(&r, val);
            return (unsigned)(r >> 3);
#elif (defined(__clang__) || (LZ4_GCC_VERSION >= 304)) && !defined(LZ4_FORCE_SW_BITCOUNT)
            return (__builtin_clzll((U64)val) >> 3);
#else
            unsigned r;
            if (!(val >> 32)) {
                r = 4;
            } else {
                r = 0;
                val >>= 32;
            }
            if (!(val >> 16)) {
                r += 2;
                val >>= 8;
            } else {
                val >>= 24;
            }
            r += (!val);
            return r;
#endif
        } else /* 32 bits */
        {
#if defined(_MSC_VER) && !defined(LZ4_FORCE_SW_BITCOUNT)
            unsigned long r = 0;
            _BitScanReverse(&r, (unsigned long)val);
            return (unsigned)(r >> 3);
#elif (defined(__clang__) || (LZ4_GCC_VERSION >= 304)) && !defined(LZ4_FORCE_SW_BITCOUNT)
            return (__builtin_clz((U32)val) >> 3);
#else
            unsigned r;
            if (!(val >> 16)) {
                r = 2;
                val >>= 8;
            } else {
                r = 0;
                val >>= 24;
            }
            r += (!val);
            return r;
#endif
        }
    }
}