log2_fp()

static FASTLED_FORCE_INLINE u16x16 fl::u16x16::log2_fp ( u16x16 x )

inlinestaticprivate

Definition at line 230 of file u16x16.h.

                                                                      {
        u32 val = x.mValue;
        int msb = highest_bit(val);
        if (msb < 0) return u16x16();  // log2(0) = undefined, return 0
 
        u32 int_part = msb - FRAC_BITS;
        u32 t;
        if (msb >= FRAC_BITS) {
            t = (val >> (msb - FRAC_BITS)) - (SCALE);
        } else {
            t = (val << (FRAC_BITS - msb)) - (SCALE);
        }
 
        // 2-term polynomial coefficients for log2(1+t), t in [0,1).
        // Stored as u64 with 24 fractional bits.
        constexpr int IFRAC = 24;
        constexpr u64 c0 = 24189248ULL;  // 1.44179 * 2^24
        constexpr u64 c1 = 5049984ULL;   // 0.30093 * 2^24
 
        // Extend t from 16 to 24 frac bits.
        u64 t24 = static_cast<u64>(t) << (IFRAC - FRAC_BITS);
 
        // Simplified Horner: c0 + c1*t, then multiply by t
        u64 acc = c0 + ((c1 * t24) >> IFRAC);
        u64 frac_part = (acc * t24) >> IFRAC;
 
        // Convert from 24 frac bits back to 16.
        u32 frac16 = static_cast<u32>(frac_part >> (IFRAC - FRAC_BITS));
        return from_raw((int_part << FRAC_BITS) + frac16);
    }

References u16x16(), FASTLED_FORCE_INLINE, fl::FL_NO_EXCEPT, FRAC_BITS, from_raw(), highest_bit(), SCALE, fl::t, and fl::x.

Referenced by pow().

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