exp2_fp()

static FASTLED_FORCE_INLINE s12x4 fl::s12x4::exp2_fp ( s12x4 x )

inlinestaticprivate

Definition at line 345 of file s12x4.h.

                                                                   {
        s12x4 fl_val = floor(x);
        s12x4 fr = x - fl_val;
        i32 n = fl_val.mValue >> FRAC_BITS;
        if (n >= INT_BITS - 1) return from_raw(0x7FFF);
        if (n < -FRAC_BITS) return s12x4();
        i32 int_pow;
        if (n >= 0) {
            int_pow = static_cast<i32>(SCALE) << n;
        } else {
            int_pow = static_cast<i32>(SCALE) >> (-n);
        }
        // 4-term minimax coefficients for 2^t - 1, t in [0,1).
        // Stored as i32 with 12 fractional bits.
        constexpr int IFRAC = 12;
        constexpr i32 d0 = 2839;    // 0.69316 * 2^12
        constexpr i32 d1 = 986;     // 0.24071 * 2^12
        constexpr i32 d2 = 219;     // 0.05336 * 2^12
        constexpr i32 d3 = 52;      // 0.01276 * 2^12
        // Extend fr from 4 to 12 frac bits.
        i32 fr12 = static_cast<i32>(fr.mValue) << (IFRAC - FRAC_BITS);
        // Horner: 1 + fr * (d0 + fr * (d1 + fr * (d2 + fr * d3)))
        i32 acc = d3;
        acc = d2 + ((acc * fr12) >> IFRAC);
        acc = d1 + ((acc * fr12) >> IFRAC);
        acc = d0 + ((acc * fr12) >> IFRAC);
        constexpr i32 one12 = 1 << IFRAC;
        i32 frac_pow12 = one12 + ((acc * fr12) >> IFRAC);
        // Convert from 12 frac bits to 4 frac bits, then scale by int_pow.
        i32 frac_pow4 = frac_pow12 >> (IFRAC - FRAC_BITS);
        i32 result =
            (int_pow * frac_pow4) >> FRAC_BITS;
        return from_raw(static_cast<i16>(result));
    }

References s12x4(), FASTLED_FORCE_INLINE, FL_NOEXCEPT, floor(), FRAC_BITS, from_raw(), INT_BITS, mValue, SCALE, and fl::x.

Referenced by pow().

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