log2_fp()

static FASTLED_FORCE_INLINE u24x8 fl::u24x8::log2_fp ( u24x8 x )

inlinestaticprivate

Definition at line 208 of file u24x8.h.

                                                                   {
        u32 val = x.mValue;
        int msb = highest_bit(val);
        if (msb < 0) return u24x8();  // 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);
        }
 
        // Simplified 2-term minimax coefficients for log2(1+t), t in [0,1).
        // Stored as u64 with 16 fractional bits.
        constexpr int IFRAC = 16;
        constexpr u64 c0 = 94528ULL;   // 1.44179 * 2^16
        constexpr u64 c1 = 19727ULL;   // 0.30093 * 2^16 (unsigned approximation)
 
        // Extend t from 8 to 16 frac bits.
        u64 t16 = static_cast<u64>(t) << (IFRAC - FRAC_BITS);
 
        // Horner for unsigned: simplified polynomial
        u64 acc = c0 + ((c1 * t16) >> IFRAC);
        u64 frac_part = (acc * t16) >> IFRAC;
 
        // Convert from 16 frac bits back to 8.
        u32 frac8 = static_cast<u32>(frac_part >> (IFRAC - FRAC_BITS));
        return from_raw((int_part << FRAC_BITS) + frac8);
    }

References u24x8(), FASTLED_FORCE_INLINE, FL_NOEXCEPT, FRAC_BITS, from_raw(), highest_bit(), SCALE, fl::t, and fl::x.

Referenced by pow().

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